10-Bit, 12-Channel Decimating
LCD DECDRIVER
®
with Level Shifters
AD8385
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703
© 2005 Analog Devices, Inc. All rights reserved.
FEATURES
High voltage drive to within 1.3 V of supply rails
Output short-circuit protection
High update rates
Fast, 100 Ms/s 10-bit input data update rate
Static power dissipation: 1.84 W
Voltage controlled video reference (brightness), offset,
and full-scale (contrast) output levels
INV bit reverses polarity of video signal
3.3 V logic, 9 V to 18 V analog supplies
Level shifters for panel timing signals
High accuracy voltage outputs
Laser trimming eliminates the need for adjustments or
calibration
Flexible logic
STSQ/XFR allow parallel AD8385 operation
Fast settling into capacitive loads
30 ns settling time to 0.25% into 150 pF load
Slew rate 460 V/µs
Available in 100-lead 14 mm × 14 mm TQFP E-pad
GENERAL DESCRIPTION
The AD8385 provides a fast, 10-bit, latched decimating digital
input that drives 12 high voltage outputs. 10-bit input words are
loaded into 12 separate high speed, bipolar DACs sequentially.
Flexible digital input format allows several AD8385s to be used
in parallel in high resolution displays. The output signal can be
adjusted for dc reference, signal inversion, and contrast for
maximum flexibility. Integrated level shifters convert timing
signals from a 3 V timing controller to high voltage for LCD
panel timing inputs. Two, serial, 8-bit DACs are integrated to
provide dc reference signals. A 3-wire serial interface controls
overload protection, output mode, and the serial DACs.
The AD8385 is fabricated on ADI's fast bipolar, 26 V XFHV
process, which provides fast input logic, bipolar DACs with
trimmed accuracy and fast settling, high voltage, precision drive
amplifiers on the same chip.
The AD8385 dissipates 1.84 W nominal static power.
The AD8385 is offered in a 100-lead, 14 mm × 14 mm TQFP
E-pad package and operates over the commercial temperature
range of 0°C to 85°C.
FUNCTIONAL BLOCK DIAGRAM
BYP
DYIN
DIRYIN
DIRXIN
NRGIN
DXIN
ENBX1I
ENBX2I
ENBX3I
ENBX4I
CLXIN
CLYIN
MONITI
SVRH
SVRL
SVRL
SDI
SCL
SEN
VRH
VRH
VRL
R/L
CLK
STSQ
XFR
DB(0:9)
INV
V1
V2
TSTM
CLX
CLY
CLXN
CLYN
MONITO
AD8385
VAO1
VAO2
VID0
VID1
VID2
VID3
VID4
VID5
VID6
VID7
VID8
VID9
VID10
VID11
DY
DIRY
DIRX
NRG
DX
ENBX1
ENBX2
ENBX3
ENBX4
SCALING
CONTROL
SEQUENCE
CONTROL
BIAS
DACs
2-STAGE
LATCH
INV
CONTROL
12-BIT
SHIFT
REGISTER
DUAL
DAC
S
R
9
/
2
/
3
/
3
/
3
/
4
/
10
/
9
/
2
/
2
/
12
/
04514-
0-
001
Figure 1.
AD8385
Rev. 0 | Page 2 of 24
TABLE OF CONTENTS
Specifications..................................................................................... 3
DECDRIVER Section .................................................................. 3
Level Shifters ................................................................................. 4
Level Shifting Edge Detector ...................................................... 5
Serial Interface .............................................................................. 5
Power Supplies .............................................................................. 6
Operating Temperature ............................................................... 6
Absolute Maximum Ratings............................................................ 7
ESD Caution.................................................................................. 7
Overload Protection..................................................................... 8
Exposed Paddle............................................................................. 8
Maximum Power Dissipation ..................................................... 8
Operating Temperature Range ................................................... 8
Pin Configuration and Function Descriptions............................. 9
Block Diagrams and Timing Diagrams ....................................... 11
DECDRIVER Section ................................................................ 11
Level Shifters ............................................................................... 13
Level Shifting Edge Detector .................................................... 14
Serial Interface ............................................................................ 15
Functional Description .................................................................. 16
Reference and Control Input .................................................... 16
Output Operating Mode............................................................ 17
Overload Protection................................................................... 17
Serial DACs ................................................................................. 17
Theory of Operation ...................................................................... 18
Transfer Function and Analog Output Voltage ...................... 18
Accuracy ...................................................................................... 18
Applications..................................................................................... 19
Optimized Reliability with the Thermal Switch..................... 19
Operation in High Ambient Temperature .............................. 20
Power Supply Sequencing ......................................................... 20
VBIAS Generation--V1, V2 Input Pin Functionality ........... 20
Applications Circuit ................................................................... 21
PCB Design for Optimized Thermal Performance ............... 21
Thermal Pad Design .................................................................. 21
Thermal Via Structure Design.................................................. 21
AD8385 PCB Design Recommendations ............................... 22
Outline Dimensions ....................................................................... 23
Ordering Guide .......................................................................... 23
REVISION HISTORY
1/05--Revision 0: Initial Version
AD8385
Rev. 0 | Page 3 of 24
SPECIFICATIONS
DECDRIVER SECTION
@ 25°C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, VRH = 9.5 V, VRL = V1 = V2 = 7 V, unless otherwise noted.
Table 1.
Parameter Conditions
Min
Typ
Max
Unit
VIDEO DC PERFORMANCE
1
T
MIN
to T
MAX
VDE
DAC Code 450 to 800
7.5
+7.5
mV
VCME
DAC Code 450 to 800
3.5
+3.5
mV
VIDEO OUTPUT DYNAMIC PERFORMANCE
T
MIN
to T
MAX
, V
O
= 5 V step, C
L
= 150 pF
Data Switching Slew Rate
20% to 80%
460
V/µs
Invert Switching Slew Rate
20% to 80%
560
V/µs
Data Switching Settling Time to 1%
19
24
ns
Data Switching Settling Time to 0.25%
30
50
ns
Invert Switching Settling Time to 1%
75
120
ns
Invert Switching Settling Time to 0.25%
250
500
ns
Invert Switching Overshoot
100
200
mV
CLK and Data Feedthrough
2
10
mV
p-p
All-Hostile Crosstalk
3
Amplitude
10
mV
p-p
Glitch Duration
30
ns
DAC Transition Glitch Energy
DAC Code 511 to 512
0.3
nV-s
VIDEO OUTPUT CHARACTERISTICS
Output Voltage Swing
AVCC VOH, VOL AGND
1.1
1.3
V
Output Voltage--Grounded Mode
0.25
V
Data Switching Delay: t
9
4
50 % of VIDx
10
12
14
ns
INV Switching Delay: t
10
5
50 % of VIDx
13
15
17
ns
INV to CLK Setup Time: t
27
0.5
f
CLK
5.5
f
CLK
ns
Output Current
100
mA
Output Resistance
22
REFERENCE INPUTS
V1 Range
V2
(V1 0.25 V)
5
AVCC 4
V
V2 Range
V2
(V1 0.25 V)
5
AVCC 4
V
V1 Input Current
5
µA
V2 Input Current
27
µA
VRL Range
VRH VRL
V1 0.5
AVCC 1.3
V
VRH Range
VRH VRL
VRL
AVCC
V
VRH to VRL Range
VFS =2 × (VRH VRL)
0
2.75
V
VRH Input Resistance
To VRL
20
k
VRL Bias Current
0.2
µA
VRH Input Current
125
µA
RESOLUTION
Coding Binary
10
Bits
AD8385
Rev. 0 | Page 4 of 24
Parameter Conditions
Min
Typ
Max
Unit
DIGITAL INPUT CHARACTERISTICS
Input t
r
, t
f
= 2 ns
Max. Input Data Update Rate
100
Ms/s
Data Setup Time: t
1
0
ns
STSQ Setup Time: t
3
0
ns
XFR Setup Time: t
5
0
ns
Data Hold Time: t
2
3
ns
STSQ Hold Time: t
4
3
ns
XFR Hold Time: t
6
3
ns
CLK High Time: t
7
3
ns
CLK Low Time: t
8
2.5
ns
C
IN
3
pF
I
IH
0.05
µA
I
IL
0.6
µA
V
IH
2
V
V
IL
0.8
V
V
TH
1.65
V
1
VDE = differential error voltage; VCME = common-mode error voltage; VFS = full-scale output voltage = 2 × (VRH VRL). See the
section.
Accuracy
2
Measured on two outputs differentially as CLK and DB(0:9) are driven and XFR is held low.
3
Measured on two outputs differentially as the other four are transitioning by 5 V. Measured for both states of INV.
4
Measured from 50% of rising CLK edge to 50% of output change. Measurement is made for both states of INV.
5
Measured from 50% of rising CLK edge that follows a valid XFR to 50% of output change. Refer to
for the definition.
Figure 6
LEVEL SHIFTERS
@ 25°C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, VRH = 9.5 V, VRL = V1 = V2 = 7 V, unless otherwise noted.
Table 2.
Parameter Conditions
Min
Typ
Max
Unit
LEVEL SHIFTER LOGIC INPUTS
C
IN
3
pF
I
IH
0.05
2
µA
I
IL
2
0.6
µA
V
TH
1.65
V
V
IH
2.0
DVCC
V
V
IL
DGND
0.8
V
LEVEL SHIFTER OUTPUTS
R
L
> 10 k
V
OH
AVCC 0.25
V
V
OL
0.25
V
LEVEL SHIFTER DYNAMIC PERFORMANCE
T
A MIN
to T
A MAX
Output Rise, Fall Times--t
r
, t
f
DX, CLX, CLXN, ENBX[14]
C
L
= 40 pF
18.5
30
ns
DY, CLY, CLYN
C
L
= 40 pF
40
70
ns
DIRX, DIRY
C
L
= 40 pF
102
200
ns
NRG
C
L
= 200 pF
43
50
ns
NRG
C
L
= 300 pF
61
100
ns
Propagation Delay Times--t
11
, t
12
, t
13
, t
14
DX, CLX, CLXN, ENBX[14]
C
L
= 40 pF
20
50
ns
DY, CLY, CLYN
C
L
= 40 pF
29
50
ns
DIRX, DIRY
C
L
= 40 pF
70
100
ns
NRG
C
L
= 200 pF
30
100
ns
NRG C
L
= 300 pF
37
ns
Output Skew
ENBX[1-4]--t
15
, t
16
C
L
= 40 pF
2
ns
DX to ENBX[14]--t
16
C
L
= 40 pF
2
ns
DX to CLX--t
15
, t
16
, t
17
, t
18
C
L
= 40 pF
10
ns
DY, CLY, CLYN--t
15
, t
16
, t
17
, t
18
C
L
= 40 pF
20
ns
AD8385
Rev. 0 | Page 5 of 24
LEVEL SHIFTING EDGE DETECTOR
@ 25°C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, VRH = 9.5 V, VRL = V1 = V2 = 7 V, unless otherwise noted.
Table 3.
Parameter Conditions
Min
Typ
Max
Unit
V
IL
Input Low Voltage
AGND
AGND + 0.75
V
V
IH
Input High Voltage
AVCC 0.7
AVCC
V
V
TH LH
Input Rising Edge Threshold Voltage
AGND + 1
V
V
TH HL
Input Falling Edge Threshold Voltage
AVCC 1
V
V
OH
Output High Voltage
DVCC
- 0.25
V
V
OL
Output Low Voltage
0.25
V
I
IH
Input Current High State
1.2
2.5
µA
I
IL
Input Current Low State
2.5
1.2
µA
t
19
Input Rising Edge Propagation Delay Time
C
L
= 10 pF
16
ns
t
19
t
19
Variation with Temperature
2
ns
t
20
Input Falling Edge Propagation Delay Time
C
L
= 10 pF
12
ns
t
20
t
20
Variation with Temperature
2
ns
t
r
Output Rise Time
10% to 90%
5
ns
t
f
Output Fall Time
10% to 90%
6
ns
SERIAL INTERFACE
@ 25 C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, SVFS = 5 V, SVRL = 4 V, SVRH = 9 V, unless otherwise noted.
Table 4.
Parameter Conditions
Min
Typ
Max
Unit
SERIAL DAC REFERENCE INPUTS
SVFS = (SVRH SVRL)
SVRH Range
SVRL SVRH
SVRL + 1
AVCC 3.5
V
SVRL Range
SVRL SVRH
AGND + 1.5
SVRH 1
V
SVFS Range
1
8
V
SVRH Input Current
SVFS = 5 V
125
150
µA
SVRL Input Current
SVFS = 5 V
2.8
2.5
mA
SVRH Input Resistance
40
k
SERIAL DAC ACCURACY
DNL
SVFS = 5 V, R
L
=
1.0
+1.0
LSB
INL
SVFS = 5 V, R
L
=
1.5
+1.5
LSB
Output Offset Error
2.0
+2.0
LSB
Scale Factor Error
3
+3
LSB
SERIAL DAC LOGIC INPUTS
Input t
r
, t
f
= 10 ns
C
IN
3
pF
I
IN LOW
Low Level Input Current
0.6
µA
I
IN HIGH
High Level Input Current
0.05
µA
V
TH
Input Threshold Voltage
1.65
V
V
IH
Input High Voltage
2.0
DVCC
V
V
IL
Input Low Voltage
DGND
0.8
V
SERIAL DAC OUTPUTS
Maximum Output Voltage
SVRH 1 LSB
V
Minimum Output Voltage
SVRL
V
VAO1--Grounded Mode
0.1
V
I
OUT
±30
mA
C
LOAD
Low Range
1
0.002
µF
C
LOAD
High Range
1
0.047
µF
AD8385
Rev. 0 | Page 6 of 24
Parameter Conditions
Min
Typ
Max
Unit
SERIAL INTERFACE DYNAMIC PERFORMANCE
SEN to SCL Setup Time, t
20
10
ns
SCL, High Level Pulse Width, t
21
10
ns
SCL, Low Level Pulse Width, t
22
10
ns
SDI Setup Time, t
24
10
ns
SDI Hold Time, t
25
10
ns
SCL to SEN Hold Time, t
23
10
ns
VAO1, VAO2 Settling Time, t
26
SVFS = 5 V, to 0.5%, C
L
= 100 pF
1
2
ms
VAO1, VAO2 Settling Time, t
26
SVFS = 5 V, to 0.5%, C
L
= 33 µF
15
ms
1
Outputs VAO1 and VAO2 are designed to drive very high capacitive loads. For proper operation of these outputs, load capacitance must be 0.002 µF or 0.047 µF.
Load capacitance in the range of 0.002 µF to 0.047 µF causes the output overshoot to exceed 100 mV.
POWER SUPPLIES
@ 25°C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, SVFS = 5 V, SVRL = 4 V, SVRH = 9 V, unless otherwise noted.
Table 5.
AD8385 Power Supplies
Min
Typ
Max
Unit
DVCC, Operating Range
3
3.3
3.6
V
DVCC, Quiescent Current
56
mA
AVCC Operating Range
9
18
V
Total AVCC Quiescent Current
111
mA
OPERATING TEMPERATURE
@ 25°C, AVCC = 15.5 V, DVCC = 3.3 V, T
A MIN
= 0°C, T
A MAX
= 85°C, SVFS = 5 V, SVRL = 4 V, SVRH = 9 V, unless otherwise noted.
Table 6.
Parameter Min
Typ
Max
Unit
Ambient Temperature Range, T
A
1
0 75
°C
Ambient Temperature Range, T
A
2
0 85
°C
1
Operation at high ambient temperature requires a thermally-optimized PCB layout (see the
section), input data update rate not exceeding 85 MHz, black-
to-white transition 4 V and C
Applications
L
150 pF. In systems with limited or no airflow, the maximum ambient operating temperature is limited to 75°C with the overload
protection enabled. For operation above 75°C, see Endnote 2.
2
In addition to the requirements stated in Endnote 1, operation at 85°C ambient temperature requires 200 lfm airflow or the overload protection disabled.
AD8385
Rev. 0 | Page 7 of 24
ABSOLUTE MAXIMUM RATINGS
Table 7.
Parameter Rating
Supply Voltage
AVCCx AGNDx
18 V
DVCC DGND
4.5 V
Input Voltage
Maximum Digital Input Voltage
DVCC + 0.5 V
Minimum Digital Input Voltage
DGND 0.5 V
Maximum Analog Input Voltage
AVCC + 0.5 V
Minimum Analog Input Voltage
AGND 0.5 V
Internal Power Dissipation
1
TQFP E-Pad Package @ T
A
= 25°C
5.00 W
Operating Temperature Range
0°C to 85°C
Storage Temperature Range
65°C to 125°C
Lead Temperature Range (Soldering, 10 sec)
300°C
Stresses above those listed under the Absolute Maximum
Ratings may cause permanent damage to the device. This is a
stress rating only; functional operation of the device at these or
any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to the
absolute maximum ratings for extended periods may reduce
device reliability.
1
100-lead TQFP E-pad package:
JA
= 20°C/W (still air),
JEDEC STD, 4-layer PCB in still air.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
AD8385
Rev. 0 | Page 8 of 24
OVERLOAD PROTECTION
The AD8385 employs a 2-stage overload protection circuit with
an enable/disable function that is programmable through the
3-wire serial interface. It consists of an output current limiter
and a thermal shut down.
When enabled, the maximum current at any one output of the
AD8385 is, on average, internally limited to 100 mA. In the
event of a momentary short circuit between a video output and
a power supply rail (VCC or AGND), the output current limit is
sufficiently low to provide temporary protection.
The thermal shutdown debiases the output amplifier when the
junction temperature reaches the internally set trip point. In the
event of an extended short circuit between a video output and a
power supply rail, the output amplifier current continues to
switch between 0 mA and 100 mA typ, with a period deter-
mined by the thermal time constant and the hysteresis of the
thermal trip point. Thermal shutdown provides long-term
protection by limiting the average junction temperature to a
safe level. When disabled, no overload protection is present.
EXPOSED PADDLE
To ensure optimal thermal performance, the exposed paddle
must be electrically connected to an external plane such as
AVCC or GND, as described in the Applications Circuit section.
MAXIMUM POWER DISSIPATION
The junction temperature limits the maximum power that can
be safely dissipated by the AD8385. The maximum safe junction
temperature for plastic encapsulated devices, determined by the
glass transition temperature of the plastic, is approximately
150°C. Exceeding this limit can cause a temporary shift in the
parametric performance due to a change in the stresses exerted
on the die by the package. Exceeding a junction temperature of
175°C for an extended period can result in device failure.
OPERATING TEMPERATURE RANGE
The maximum operating junction temperature is 150°C. The
junction temperature trip point of the overload protection is
165°C. Production test guarantees a minimum junction
temperature trip point of 125°C.
Consequently, the maximum guaranteed operating junction
temperature is 125°C with the overload protection enabled, and
150°C with the overload protection disabled.
To ensure operation within the specified operating temperature
range, the maximum power dissipation must be limited:
(
)
)
9
.
0
(
3
lfm
in
Airflow
T
T
P
JA
A
JMAX
DMAX
×
-
-
M
A
XIM
U
M
POW
E
R
D
I
SSIPA
TION
(
W
)
1.5
2.5
2.0
3.0
85
80
70
75
*65
90
95
100
105
110
105
95
100
**90
115
120
125
130
AMBIENT TEMPERATURE (°C)
04514-0-002
STILL AIR
200 lfm
500 lfm
100MHz
60Hz XGA
QUIESCENT
*OVERLOAD PROTECTION ENABLED
**OVERLOAD PROTECTION DISABLED
AD8385 on a 4-layer JEDEC PCB with a thermally optimized landing pattern,
as described in the Applications Circuit section.
Figure 2. Maximum Power Dissipation vs. Temperature
Note that the quiescent power dissipation of the AD8385 is
1.84 W when operating under the conditions specified in this
data sheet. When driving a 12-channel XGA panel with an input
capacitance of 150 pF, the AD8385 dissipates a total of 2.3 W
when displaying 1 pixel wide alternating white and black
vertical lines generated by a standard 60 Hz XGA input video.
When the frequency of the pixel clock is raised to 100 MHz, the
total power dissipation increases to 2.54 W. These specific
power dissipations are shown in Figure 2 for reference.
AD8385
Rev. 0 | Page 9 of 24
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
DVCC
DGND
SDI
SEN
SCL
BYP
TSTM
AGNDS
AGNDS
SVRL
SVRL
SVRH
VAO1
VAO2
AVCCS
NC
DIRX
DIRY
DY
CLY
CLYN
DIRXIN
DIRYIN
DYIN
CLYIN
AV
CCL
NRGIN
NRG
AGNDL
MO
NI
TI
NC
MO
NI
TO
DX
IN
EN
B
X
1I
EN
B
X
2I
EN
B
X
4I
CLX
I
N
DX
E
NBX
1
E
NBX
2
EN
B
X
3I
E
NBX
3
E
NBX
4
CLX
CLX
N
NC
TSTA
DGND
DGND
DV
CC
AGND0
VID0
AVCC0,2
VID2
AGND2,4
VID4
AVCC4,6
VID6
AGND6,8
VID8
AVCC8,10
VID10
AGND10,1
VID1
AVCC1,3
VID3
AGND3,5
VID5
AVCC5,7
VID7
AGND7,9
VID9
AVCC9,11
VID11
AGND11
R/L
INV
STSQ
XFR
CLK
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
NC
NC
AGNDD
AV
CCD
VR
H
VR
H
VR
L
V2
V1
NC
04514-0-003
1
2
3
4
5
6
7
8
9
10
11
13
14
15
16
12
17
18
20
19
21
22
23
25
24
100 99 98 97 96
91 90 89 88 87 86 85
95 94 93 92
84 83 82 81 80 79 78 77 76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
PIN 1
IDENTIFIER
AD8385
TOP VIEW
(Not to Scale)
100L
14mm x 14mm
TQFP E-PAD
NC =
NO CONNECT
Figure 3. 100-Lead TQFP Package
Table 8. Pin Function Descriptions
Pin Name
Function
Description
DB(0:9) Data
Input
10-Bit
Data Input. MSB = DB9.
CLK
Clock
Clock Input. Data is acquired on both edges of the CLK.
STSQ Start
Sequence
A new data loading sequence begins on the rising edge of CLK when this input was high on the
preceding rising edge of CLK.
R/L Right/Left
Select
A new data loading sequence begins on the left, with Channel 0, when this input is low; a new
data loading sequence begins on the right, with Channel 11 when this input is high.
XFR Data
Transfer
Data is transferred to the video outputs on the next rising edge of CLK when this input is high on
the rising edge of CLK.
VID0VID11
Analog Outputs
These pins are directly connected to the analog inputs of the LCD panel.
V1, V2
Reference Voltages
The voltage applied between V1 and AGND sets the white video level during INV = low. The
voltage applied between V2 and AGND sets the white video level during INV = high.
VRH, VRL
Full-Scale
References
The voltage applied between these pins sets the full-scale video output voltage.
INV Invert
When this input is high, the analog output voltages are above V2. When low, the analog outputs
voltages are below V1.
DVCC
Digital Power Supply
Digital Power Supply.
DGND
Digital Ground
This pin is normally connected to the digital ground plane.
AVCCx
Analog Power
Supplies
Analog Power Supplies.
AGNDx
Analog Ground
Analog Supply Returns.
BYP
Bypass
A 0.1 µF capacitor connected between this pin and AGND ensures optimum settling time.
SVRH, SVRL
Serial DAC Reference
Voltages
Reference Voltages for the Output Amplifiers of the Serial DACs.
AD8385
Rev. 0 | Page 10 of 24
Pin Name
Function
Description
SCL
Serial Interface Data
Clock
Clock for the Serial Interface.
SDI
Serial Interface Data
Input
While the SEN input is low, one 12-bit serial word is loaded into the serial interface on the rising
edges of SCL. The first four bits select the function; the following eight bits are the data used in the
serial DACs.
SEN
Serial Interface
Enable
A falling edge of this input initiates a loading cycle. While this input is held low, the serial interface
is enabled and data is loaded on every rising edge of SCL. The selected functions are updated on
the rising edge of this input. While this input is held high, the serial interface is disabled.
VAO1, VAO2
Serial DAC Voltage
Output
These output voltages are updated on the rising edge of the SEN input.
TSTM Test
Mode When this input is low, the overload protection and output mode are determined by the function
programmed into the serial interface. While this input is held high, the overload protection is
forced to enabled and the output mode is forced to normal, regardless of function programmed
into the serial interface.
TSTA
Test Pin
Connect this pin to DGND.
MONITI Monitor
Input Logic
Input of the Level Shifting Inverting Edge Detector.
MONITO Monitor
Output
Output of the Level Shifting Inverting Edge Detector.
DYIN, DIRYIN,
DIRXIN, DXIN,
NRGIN,
ENBX(14)IN
Inverting Level
Shifter Inputs
Logic Input of the Inverting Level Shifters.
DX, DY, DIRX,
DIRY, NRG,
ENBX(14)
Inverting Level
Shifter Outputs
While the corresponding input voltage of these level shifters is below the threshold voltage, the
output voltage at these pins is at VOH. While the corresponding input voltage of these level
shifters is above the threshold voltage, the output voltage at these pins is at VOL.
CLXIN, CLYIN
Complementary
Level Shifter Inputs
Logic Input of the Complementary Level Shifters.
CLX, CLXN,
CLY, CLYN,
Complementary
Level Shifter
Outputs
While the corresponding input voltage of these level shifters is below the threshold voltage, the
voltage at the noninverting output pins is at VOH and the voltage at the inverting outputs is at
VOL. While the corresponding input voltage of these level shifters is above the threshold voltage,
the voltage at the noninverting output pins is at VOL and the voltage at the inverting outputs is at
VOH.
AD8385
Rev. 0 | Page 11 of 24
BLOCK DIAGRAMS AND TIMING DIAGRAMS
DECDRIVER SECTION
VRH VRL
VID4
VID6
VID8
VID10
VID2
VID0
AD8385
BYP
R/L
CLK
STSQ
XFR
INV
V1
V2
DB(0:9)
SCALING
CONTROL
SEQUENCE
INV CONTROL
CONTROL
BIAS
04514-0-004
2-STAGE
2-STAGE
2-STAGE
2-STAGE
2-STAGE
2-STAGE
LATCH
LATCH
LATCH
LATCH
LATCH
LATCH
DAC
DAC
DAC
DAC
DAC
DAC
10
10
10
10
10
10
10
10
10
10
VID3
VID5
VID7
VID9
VID1
2-STAGE
2-STAGE
2-STAGE
2-STAGE
2-STAGE
LATCH
LATCH
LATCH
LATCH
LATCH
DAC
DAC
DAC
DAC
DAC
10
10
10
10
10
10
10
10
VID11
2-STAGE
LATCH
DAC
10
10
10
10
10
10
10
10
Figure 4. Block Diagram
AD8385
Rev. 0 | Page 12 of 24
CLK
DB(0:9)
STSQ
XFR
V
TH
t
r
t
r
t
8
t
7
t
2
t
1
t
1
V
TH
V
TH
V
TH
t
4
t
3
t
6
t
5
04514-0-005
t
2
Figure 5. Input Timing
CLK
STSQ
XFR
INV
VID(0:11)
V2
0
1
2
3
4
5
6
7
8
9
1
2
3
5
6
7
8
9 10 11 12 13 14 15
4
V2+VFS
DB(0:9)
50%
PIXELS 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
V1
V1VFS
t
10
t
9
t
9
t
27
MIN
t
27
MAX
PIXELS 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
04514-0-006
Figure 6. Output Timing (R/L = Low)
Table 9.
Parameter Conditions
Min
Typ
Max
Unit
t
1
Data Setup Time
Input t
r
, t
f
= 2 ns
0
ns
t
2
Data Hold Time
3
ns
t
3
STSQ Setup Time
0
ns
t
4
STSQ Hold Time
3
ns
t
5
XFR Setup Time
0
ns
t
6
XFR Hold Time
3
ns
t
7
CLK High Time
3
ns
t
8
CLK Low Time
2.5
ns
t
9
Data Switching Delay
10
12
14
ns
t
10
Invert Switching Delay
13
15
17
ns
t
27
INV to CLK Setup Time
0.5/f
CLK
5.5/f
CLK
ns
AD8385
Rev. 0 | Page 13 of 24
LEVEL SHIFTERS
DYIN
DIRYIN
DIRXIN
NRGIN
DXIN
ENBX1I
ENBX2I
ENBX3I
ENBX4I
DY
DIRY
DIRX
NRG
DX
ENBX1
ENBX2
ENBX3
ENBX4
04514-0-007
Figure 7. Level Shifter--Inverting
CLXIN
CLYIN
CLX
CLY
CLXN
CLYN
04514-0-008
Figure 8. Level Shifter--Complementary
INVERTING
OUTPUTS
NONINVERTING
OUTPUTS
INPUTS
04514-0-009
t
11
t
13
t
12
t
16
t
18
t
14
t
15
t
17
Figure 9. Inverting and Complementary Level Shifter Timing
Table 10. Level Shifter Timing
Parameter Conditions
Min
Typ
Max
Unit
Output Rise, Fall Times, t
r
, t
f
T
A MIN
to T
A MAX
DX, CLX, CLXN, ENBX[14]
C
L
= 40 pF
18.5
30
ns
DY, CLY, CLYN
40
70
ns
DIRX, DIRY
102
200
ns
NRG
C
L
= 200 pF
43
50
ns
C
L
= 300 pF
61
100
ns
Propagation Delay Times--t
11
, t
12
, t
13
, t
14
T
A MIN
to T
A MAX
DX, CLX, CLXN, ENBX[14]
C
L
= 40 pF
20
50
ns
DY, CLY, CLYN
29
50
ns
DIRX, DIRY
70
100
ns
NRG C
L
= 200 pF
30
100
ns
C
L
= 300 pF
37
ns
Propagation Delay Skew--t
15
, t
16
, t
17
, t
18
T
A MIN
to T
A MAX
, C
L
= 40 pF
ENBX[14]--t
15
, t
16
2
ns
DX to ENBX[14]--t
16
2
DX to CLX--t
15
, t
16
, t
17
, t
18
10
ns
DY, CLY, CLYN--t
15
, t
16
, t
17
, t
18
20
ns
AD8385
Rev. 0 | Page 14 of 24
LEVEL SHIFTING EDGE DETECTOR
MONITI
MONITO
S
R
04514-0-010
Figure 10. Level Shifting Edge Detector Block Diagram
MONITO
MONITI
AGND
AVCC
VOL
VOH
t
19
t
20
04514-0-011
Figure 11. Level Shifting Edge Detector Timing
Table 11. Level Shifting Edge Detector, AVCC = 15.5 V, DVCC = 3.3 V, C
L
= 10 pF, T
A MIN
= 25°C, T
A MAX
= 85°C
Parameter
Min
Typ
Max
Unit
V
IL
Input Low Voltage
AGND
AGND + 0.75
V
V
IH
Input High Voltage
AVCC 0.7
AVCC
V
V
TH
LH
Input Rising Edge Threshold Voltage
AGND + 1
V
V
TH
HL
Input Falling Edge Threshold Voltage
AVCC 1
V
V
OH
Output High Voltage
DVCC 0.25
V
V
OL
Output Low Voltage
0.25
V
I
IH
Input Current High State
1.2
2.5
µA
I
IL
Input Current Low State
2.5
1.2
µA
t
19
Input Rising Edge Propagation Delay Time
16
ns
t
19
t
19
Variation with Temperature
2
ns
t
20
Input Falling Edge Propagation Delay Time
12
ns
t
20
t
20
Variation with Temperature
2
ns
t
r
Output Rise Time
5
ns
t
f
Output Fall Time
6
ns
AD8385
Rev. 0 | Page 15 of 24
SERIAL INTERFACE
SVRH
SVRL
SDI
SCL
SEN
TSTM
12-BIT SHIFT REGISTER
SD0 SD1 SD2 SD3 SD4 SD5 SD6 SD7 SD8 SD9 SD10 SD11
SD(0:7)
8
/
ENABLE
THERMAL
SWITCH
12
/
VIDEO
DACs
DUAL SDAC
SELECT LOAD
CONTROL
VAO1, VAO2 = SVRL + SDICODE (SVRHSVRL)/256
12
/
AO2
AO1
VID(0:11)
04514-0-012
6
/
Figure 12. Serial Interface Block Diagram
SCL
SEN
SDI
D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
04514-
0-
013
VAO1,
VAO2
Figure 13. Serial Interface Timing
SEN
SCL
SDI
VAO1,
VAO2
t
20
t
24
t
25
t
26
t
21
t
22
t
23
D11
D0
D1
D10
04514-
0-
014
Figure 14. Serial Interface Timing
Table 12. Serial DAC Timing
Parameter Conditions
Min
Typ
Max
Unit
SEN to SCL Setup Time, t
20
10
ns
SCL, High Level Pulse Width, t
21
10
ns
SCL, Low Level Pulse Width, t
22
10
ns
SDI Setup Time, t
24
10
ns
SDI Hold Time, t
25
10
ns
SCL to SEN Hold Time, t
23
10
ns
VAO1, VAO2 Settling Time, t
26
VFS = 5 V, to 0.5%, C
L
= 100 pF
1
2
ms
VFS = 5 V, to 0.5%, C
L
= 33 µF
15
ms
AD8385
Rev. 0 | Page 16 of 24
FUNCTIONAL DESCRIPTION
The AD8385 is a system building block designed to directly
drive the columns of LCD microdisplays of the type popu-
larized for use in projection systems. It comprises 12 channels
of precision, 10-bit digital-to-analog converters loaded from a
single, high speed, 10-bit wide input. Precision current feedback
amplifiers, providing well-damped pulse response and fast
voltage settling into large capacitive loads, buffer the 12 outputs.
Laser trimming at the wafer level ensures low absolute output
errors and tight channel-to-channel matching. Tight part-to-
part matching in high resolution systems is guaranteed by the
use of external voltage references.
Three groups of level shifters convert digital inputs to high
voltage outputs for direct connection to the control inputs of
LCD panels.
An edge detector conditions a high voltage reference timing
input from the LCD and converts it to digital levels for use in
synchronizing timing controllers, such as the AD8389.
REFERENCE AND CONTROL INPUT
Start Sequence Control--Input Data Loading
A valid STSQ control input initiates a new 6-clock loading cycle
during which 12 input data-words are loaded sequentially into
12 internal channels. Data is loaded on both the rising and
falling edges of CLK. A new loading sequence begins on the
current rising CLK edge only when STSQ is held high at the
preceding rising CLK edge.
Right/Left Control--Input Data Loading
To facilitate image mirroring, the direction of the loading
sequence is set by the R/L control.
A new loading sequence begins at Channel 0 and proceeds to
Channel 11 when the R/L control is held low. It begins at
Channel 11 and proceeds to Channel 0 when the R/L control
is held high.
XFR Control--Data Transfer to Outputs
Data transfer to the outputs is initiated by the XFR control. Data
is transferred to all outputs simultaneously on the rising CLK
edge only when XFR is high during the preceding rising
CLK edge.
V1, V2 Inputs--Voltage Reference Inputs
Two external analog voltage references set the levels of the
outputs. V1 sets the output voltage at Code 1023 while the INV
input is low, and V2 sets the output voltage at Code 1023 while
the INV input is held high.
VRH, VRL Inputs--Full-Scale Video Reference Inputs
Twice the difference between these analog input voltages sets
the full-scale output voltage VFS = 2 (VRHVRL).
INV Control--Analog Output Inversion
The analog voltage equivalent of the input code is subtracted
from (V2 + VFS) while INV is held high and added to
(V1 VFS) while INV is held low. Video inversion is delayed
by 6 to 12 CLK cycles from the INV input.
TSTM Control--Test Mode
A low on this input allows serial interface control of the output
operating mode and the thermal switch.
A high on this input turns the thermal switch on and releases
the video outputs and VAO1 from grounded mode.
3-Wire Serial Interface--SDAC, Output, Thermal Switch
Control
The serial interface controls two 8-bit serial DACs, the thermal
switch of the overload protection circuit, and the video output
operating mode via a 12-bit-wide serial word from a micropro-
cessor. Four of the 12 bits select the function; the remaining
8 bits are the data for the serial DACs.
Table 13. Bit Definitions
Bit
Name Bit
Functionality
SD(0:7)
8-bit SDAC data. MSB = SD7
SD8 Not
used
SD9
Thermal switch control
SD10
Output operating mode, SDAC selection, and
thermal switch control
SD11
Output operating mode and SDAC selection control
Table 14. Truth Table @ TSTM = Low
SD
SEN
11 10 9 8 Action
0
0
X
X
Load VAO2. No change to VAO1.
1 0 X
X
Load VAO1. Release video outputs
from grounded mode. No change to
VAO2.
0 1 0
X
Release video outputs and VAO1 from
grounded mode. Disable thermal
switch. No change to VAO1 and
VAO2.
0 1 1
X
Release video outputs and VAO1 from
grounded mode. Enable thermal
switch. No change to VAO1 and
VAO2.
1 1 0
X
Video outputs and VAO1 to grounded
output mode. Disable thermal switch.
No change to VAO1, VAO2.
1 1 1
X
Video outputs and VAO1 to grounded
output mode. Enable thermal switch.
No change to VAO1, VAO2.
X X X
X
Start a serial interface loading cycle.
No change to outputs.
AD8385
Rev. 0 | Page 17 of 24
Table 15. Truth Table @ TSTM = High. Thermal Switch
Enabled. Grounded Output Disabled.
SD
SEN
11 10 9 8
Action
0
0
X
X
Load VAO2. No change to VAO1.
1
0
X
X
Load VAO1. No change to VAO2.
X
1
X
X
No change to VAO1 and VAO2 data.
X X X X
Start a serial interface loading cycle.
No change to outputs.
X = Don't Care.
OUTPUT OPERATING MODE
In normal operating mode, the voltage of the video outputs and
VAO1 is determined by the inputs.
In grounded output mode, the video outputs and VAO1 are
forced to (AGND + 0.1 V) typ.
OVERLOAD PROTECTION
The overload protection employs current limiters and a thermal
switch to protect the video output pins against accidental shorts
between any video output pin and AVCC or AGND.
The junction temperature trip point of the thermal switch is
165°C. Production test guarantees a minimum junction
temperature trip point of 125°C. Consequently, the operating
junction temperature should not be allowed to rise above 125°C
with the thermal switch enabled.
For systems that operate at high internal ambient temperatures
and require large capacitive loads to be driven by the AD8385 at
high frequencies, junction temperatures above 125°C may be
required. In such systems, the thermal switch should either be
disabled or a minimum airflow of 200 lfm be maintained.
SERIAL DACS
Both serial DACs are loaded via the serial interface. The output
voltage is determined by the following equation:
VAO1, VAO2 = SVRL + SD(0:7) × (SVRH SVRL)/256
Output VAO1 is designed to drive very large capacitive loads,
above 0.047 µF. Lower capacitive loads may result in excessive
overshoot at VAO1.
Level Shifters
The characteristics of the level shifters are optimized based on
their intended use.
Seven level shifters--DX, CLX, CLXN, and ENBX[1:4]--are
optimized for the X direction and three--DY, CLY and CLYN--
are optimized for the Y direction control signals.
One level shifter--NRG--is designed to drive a large capacitive
load and is optimized for an X direction control signal. Two
level shifters--DIRX and DIRY--are optimized for very low
frequency control signals.
One level shifting edge detector--MONITI, MONITO--is
optimized to condition a synchronizing feedback reference
signal from the LCD.
AD8385
Rev. 0 | Page 18 of 24
THEORY OF OPERATION
TRANSFER FUNCTION AND ANALOG OUTPUT
VOLTAGE
The DECDRIVER has two regions of operation where the video
output voltages are either above reference voltage V2 or below
reference voltage V1. The transfer function defines the video
output voltage as the function of the digital input code:
VIDx(n) = V2 + VFS × (1 n/1023), for INV = high
VIDx(n) = V1 VFS × (1 n/1023), for INV = low
where:
n = input code
VFS = 2 × (VRH VRL)
A number of internal limits define the usable range of the video
output voltages, VIDx. See Figure 15.
INPUT CODE
VID
x
(
V
)
AGND
V1 VFS
V1
V2
V2 + VFS
AVCC
0
1023
04514-0-015
0
VFS
5.5V
0
VFS
5.5V
5V
V2
(
AVCC 4)
5V
V1
(
AVCC 4)
9V
AVCC
18V
1.3V
1.3V
INV = HIGH
INV = LOW
INTERNAL LIMITS AND
USABLE VOLTAGE RANGES
VOUTN(n)
VOUTP(n)
Figure 15. Transfer Function and Usable Voltage Ranges
ACCURACY
To best correlate transfer function errors to image artifacts, the
overall accuracy of the DECDRIVER is defined by two
parameters, VDE and VCME.
VDE, the differential error voltage, measures the difference
between the rms value of the output and the rms value of the
ideal. The defining expression is
VFS
n
V
n
VOUTP
V
n
VOUTN
n
VDE
×
=
1023
1
2
]
1
)
(
[
]
2
)
(
[
)
(
VCME, the common-mode error voltage, measures ½ the dc
bias of the output. The defining expression is
(
)
+
+
=
2
2
1
)
(
)
(
2
1
2
1
)
(
V
V
n
VOUTP
n
VOUTN
n
VCME
AD8385
Rev. 0 | Page 19 of 24
APPLICATIONS
IMAGE
PROCESSOR
1/3 AD8389
CLK
DXI, CLXI,
ENBX(14)I
DXxO, CLXxO,
ENBX(14)xO
MONITxI
µ
P
AD8385
VID(0:11)
DB(0:9)
STSQ, XFR,
CLK, R/L, INV
DIRX, DIRY,
DY, CLY,
CLYN, NRG
DIRX
IN
, DIRY
IN
,
DY
IN
, CLY
IN
,
NRG
IN
MONITI
MONITO
DX,
CLX, CLXN,
ENBX (14)
DX
IN
,
CLX
IN
,
ENBX
IN
(14)
SDI
SCL
SEN
VAO1
VAO2
04514-0-016
VRH, VRL,
V1, V2,
SVRH, SVRL
DC REFERENCE
VOLTAGES
MONITOR
VCOM
LCD TIMING
CONTROLS
LCD TIMING
CONTROLS
12-CHANNEL LCD
CHANNEL 05
Figure 16. Typical Applications Circuit
OPTIMIZED RELIABILITY WITH THE THERMAL SWITCH
While internal current limiters provide short-term protection
against temporary shorts at the outputs, the thermal switch
must be enabled to protect against persistent shorts lasting for
several seconds.
Initial Power-Up After Assembly or Repair Using a
Service Jumper
To optimize reliability with the use of the thermal switch, the
following sequence of operations is recommended:
1.
Ensure that the TSTM pin is high on initial power-up by
inserting a service jumper. See Figure 17.
2.
Execute the initial power-up.
3.
Identify any shorts at outputs.
4.
Power down, repair shorts, and repeat the initial power-up
sequence until proper system functionality is verified.
5.
Remove service jumper.
6.
Resume normal operation.
DVCC
DVCC
DGND
OPTION A
OPTION B
SERVICE
JUMPER
SERVICE
JUMPER
AD8385
TSTM PIN7
AD8385
TSTM PIN7
TO
µ
P
04514-0-017
Figure 17. Service Jumper Location
Initial Power-Up after Assembly or Repair Using the
Serial Interface
1.
Immediately after power-up, send Code 011XXXXXXXXX
through the serial interface to enable the thermal switch
and disable the grounded output mode.
2.
Identify any shorts at the outputs.
3.
Power down, repair shorts, and repeat the initial power-up
sequence until proper system functionality is verified.
4.
Resume normal operation.
AD8385
Rev. 0 | Page 20 of 24
Power-Up During Normal Operation
The serial interface has no power-on reset.
Code 010XXXXXXXXX, sent immediately following
a power-up places, all outputs into normal operating
mode and disables the thermal switch.
OPERATION IN HIGH AMBIENT TEMPERATURE
To extend the maximum operating junction temperature of the
AD8385 to 150°C, keep the thermal switch disabled during
normal operation. Code format X10XXXXXXXXX ensures a
disabled thermal switch.
POWER SUPPLY SEQUENCING
As indicated in the Absolute Maximum Ratings, the voltage at
any input pin cannot exceed its supply voltage by more than
0.5 V. To ensure compliance with the Absolute Maximum
Ratings, the following power-up and power-down sequencing
is recommended.
During power-up, initial application of nonzero voltages to any
of the input pins must be delayed until the supply voltage ramps
up to its highest operational input voltage.
During power-down, the voltage at any input pin must reach
zero during a period not exceeding the hold-up time of the
power supply.
Failure to comply with the Absolute Maximum Ratings, may
result in functional failure or damage to the internal ESD
diodes. Damaged ESD diodes can cause temporary parametric
failures, which can result in image artifacts. Damaged ESD
diodes cannot provide full ESD protection, reducing reliability.
Table 16.
Power-On
Power-Off
1. Apply power to supplies.
1. Remove power from I/Os.
2. Apply power to other I/Os.
2. Remove power from supplies.
VBIAS GENERATION--V1, V2 INPUT PIN
FUNCTIONALITY
To avoid image flicker, a symmetrical ac voltage is required and
a bias voltage of approximately 1 V minimum must be
maintained across the pixels of HTPS LCDs. The AD8385
provides an internal and external method of maintaining this
bias voltage.
Internal Bias Voltage Generation
Standard systems that internally generate the bias voltage
reserve the uppermost code range for the bias voltage, and use
the remaining code range to encode the video for gamma
correction. A high degree of ac symmetry is guaranteed by the
AD8385 in these systems.
The V1 and V2 inputs in these systems are tied together and are
normally connected to VCOM, as shown in Figure 18.
VBIAS = 1V
VCOM
VFS = 5V
VFS = 5V
RESERVED
CODE
RANGE
VBIAS = 1V
V2
V1
VCOM
AD8385
04514-
0-
018
1023
820
Figure 18. V1, V2 Connection and Transfer
Function in a Typical Standard System
External Bias Voltage Generation
In systems that require improved brightness resolution and
higher accuracy, the V1 and V2 inputs, connected to external
voltage references, provide the necessary bias voltage (VBIAS)
while allowing the full code range to be used for gamma
correction.
To ensure a symmetrical ac voltage at the AD8385's outputs,
VBIAS must remain constant for both states of INV. Therefore,
V1 and V2 are defined as
V1 = VCOM VBIAS
V2 = VCOM + VBIAS
AD8385
Rev. 0 | Page 21 of 24
APPLICATIONS CIRCUIT
The following circuit ensures VBIAS symmetry to within 1 mV
with a minimum component count. Bypass capacitors are not
shown for clarity.
AVCC = 15.5V
VZ = 5.1V
DVCC = 3.3V
04514-0-019
VCOM = 7V
R1 = 6k
R2 = 1k
V2 = 8V
V1 = 6V
V2
V1
AD8385
AD8132
6
3
2
1
8
V
V+
V
OCM
IN
+IN
5
4
Figure 19. External VBIAS Generator with the AD8132
VBIAS = 1V
VCOM
V2
V1
VFS = 4V
VFS = 4V
VBIAS = 1V
1023
04514-0-020
Figure 20. AD8385 Transfer Function in a Typical High Accuracy System
5.7
6.2
6.7
7.2
7.7
8.2
8.7
9.2
9.7
10.2 10.7
8.75
6.25
3.75
1.25
3.75
6.25
7.50
8.75
1.25
7.50
5.00
0.00
2.50
5.00
2.50
(V+) (V) (V)
(V
2
+ V
1
)/
2
V
C
OM (mV
)
04514-0-021
T
A
= 85°C
T
A
= 25°C
Figure 21. Typical Asymmetry at the Outputs of the AD8132 vs. Its Power
Supply for the Application Circuit
Figure 21 shows that the AD8132 (Figure 19) typically produces
a symmetrical output at 85°C when its supply, (V+) (V), is
at 7.2 V.
PCB DESIGN FOR OPTIMIZED THERMAL
PERFORMANCE
The total maximum power dissipation of the AD8385 is partly
load-dependent. In a 12-channel 60 Hz XGA system running at
a 65 MHz pixel rate, the total maximum power dissipation is
2.3 W at an LCD channel input capacitance of 150 pF. At a
100 MHz pixel rate, the total maximum power dissipation can
exceed 3 W.
To limit the operating junction temperature at or below the
guaranteed maximum, the package, in conjunction with the
PCB, must effectively conduct heat away from the junction.
The AD8385 package is designed to provide enhanced thermal
characteristics through the exposed die paddle on the bottom
surface of the package. To take full advantage of this feature, the
exposed paddle must be in direct thermal contact with the PCB,
which then serves as a heat sink.
A thermally effective PCB must incorporate two thermal pads
and a thermal via structure. The thermal pad on the top PCB
layer provides a solderable contact surface on the top surface of
the PCB. The thermal pad on the bottom PCB layer provides a
surface in direct contact with the ambient. The thermal via
structure provides a thermal path to the inner and bottom
layers of the PCB to remove heat.
THERMAL PAD DESIGN
To minimize thermal performance degradation of production
PCBs, the contact area between the thermal pad and the PCB
should be maximized. Therefore, the size of the thermal pad on
the top PCB layer should match the exposed paddle size. The
second thermal pad of at least the same size should be placed on
the bottom side of the PCB. At least one thermal pad should be
in direct thermal contact with a plane such as AVCC or GND.
THERMAL VIA STRUCTURE DESIGN
Effective heat transfer from the top to the inner and bottom
layers of the PCB requires thermal vias incorporated into the
thermal pad design. Thermal performance increases logarith-
mically with the number of vias.
Near optimal thermal performance of production PCBs is
attained only when tightly spaced thermal vias are placed on
the full extent of the thermal pad.
AD8385
Rev. 0 | Page 22 of 24
16 mm
16 mm
6
.
5
m
m
6.5 mm
04514-0-022
AD8385 PCB DESIGN RECOMMENDATIONS
Top PCB Layer
·
Pad size: 0.25 mm × 0.25 mm
·
Pad pitch: 0.5 mm
·
Thermal pad size: 6.5 mm × 6.5 mm
·
Thermal via structure: 0.25 mm diameter vias on a
0.5 mm grid
Bottom PCB Layer
It is recommended that the bottom thermal pad be thermally
connected to a plane. The connection should be direct such that
the thermal pad becomes part of the plane.
Figure 22. Land Pattern--Top Layer
The use of thermal spokes is not recommended when con-
necting the thermal pads or via structure to the AVCC plane.
6
.
5
m
m
6.5 mm
04514-0-023
Solder Masking
To minimize the formation of solder voids due to solder flowing
into the via holes (solder wicking), the via diameter should be
small. Optional solder masking of the via holes on the top layer
of the PCB plugs the via holes, inhibiting solder flow into the
holes. To optimize the thermal pad coverage, the solder mask
diameter should be no more than 0.1 mm larger than the via
hole diameter.
Solder Mask--Top Layer
·
Pads: Set by the customer's PCB design rules
·
Thermal vias: 0.25 mm diameter circular mask, centered
on the vias.
Figure 23. Land Pattern--Bottom Layer
Solder Mask--Bottom Layer
Set by the customer's PCB design rules.
04514-0-024
Figure 24. Solder Mask--Top Layer
AD8385
Rev. 0 | Page 23 of 24
OUTLINE DIMENSIONS
Figure 25. 100-Lead, Thermally Enhanced Thin Quad Flat Package (with Exposed Heat Sink) [TQFP_EP]
(SV-100-3)
Dimensions shown in millimeters
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
AD8385ASVZ
1
0°C to 85°C
100-Lead TQFP_EP
SV-100-3
1
Z = Pb-free part.
AD8385
Rev. 0 | Page 24 of 24
NOTES
© 2005 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D0451401/05(0)
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