1
LTC1682/LTC1682-3.3/LTC1682-5
Doubler Charge Pumps with
Low Noise Linear Regulator
s
Low Output Noise: 60
µ
V
RMS
(100kHz BW)
s
Adjustable or Fixed Boosted Output
s
Adjustable Output Voltage Range: 2.5V to 5.5V
s
Fixed Output Voltages: 3.3V, 5V
s
Wide Input Voltage Range: 1.8V to 4.4V
s
Uses Small Ceramic Capacitors
s
No Inductors Required
s
Output Current up to 50mA
s
550kHz Switching Frequency
s
Low Operating Current: 150
µ
A
s
Low Shutdown Current: 1
µ
A
s
Internal Thermal Shutdown and Current Limiting
s
Available in 8-Pin MSOP and SO Packages
The LTC
®
1682/LTC1682-3.3/LTC1682-5 are doubler charge
pumps with an internal low noise, low dropout (LDO) linear
regulator. These parts are designed to provide a low noise
boosted supply voltage for powering noise sensitive devices
such as high frequency VCOs in wireless applications.
An internal doubler charge pump converts a 1.8V to 4.4V
input to a boosted output, while the internal LDO regulator
converts the boosted voltage to a low noise regulated output.
The adjustable version allows the user to set V
OUT
via external
resistors connected to FB. The regulator is capable of supply-
ing up to 50mA of output current. Shutdown reduces the
supply current to < 5
µ
A, removes the load from V
IN
by
disabling the regulator and discharges V
OUT
to ground
through a 100
switch.
The LTC1682 LDO regulator is stable with only 2
µ
F on the
output. Small ceramic capacitors can be used, reducing PC
board area.
The LTC1682/LTC1682-3.3/LTC1682-5 are short-circuit and
over temperature protected. The parts are available in 8-pin
MSOP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Open-Loop Close-In Phase Noise
CENTER = 902MHz
RES BW = 1kHz
SPAN = 100kHz
VBW = 30Hz
SWP = 10 sec
REF = 0dBm
1682 TA02
4.2V VCO Power Supply, V
IN
= 2.5V to 4.4V
s
VCO Power Supplies in Cellular Phones
s
2-Way Pagers
s
Wireless PCMCIA Cards
s
Portable Medical Instruments
s
Low Power Data Acquisition
s
Remote Transmitters
AMPLITUDE
10dB/DIV
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
36k
SHUTDOWN
15k
100k
4.7
µ
F
0.22
µ
F
V
IN
2.5V TO
4.4V
4.7
µ
F
4.2V
1
2
3
4
8
7
6
5
V
OUT
SHDN
FB
GND
CPO
C
+
V
IN
C
1682 TA01
LTC1682
VCO
MURATA
MQE001-902
1
µ
F
4.7
µ
F
1000pF
1k
B
M
P
C
1000pF
1000pF
4.7
µ
F
V
C
f
OUT
902MHz
2
LTC1682/LTC1682-3.3/LTC1682-5
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are T
A
= 25
°
C. SHDN = V
IN
= 3V; C1 = 0.22
µ
F; C2, C3, C4 = 4.7
µ
F, unless otherwise noted.
(Note 1)
V
IN
to Ground .............................................. 0.3V to 5V
V
OUT
Voltage ................................................ 0.3V to 6V
CPO to Ground ........................................................ 10V
SHDN, FILT/FB Voltage to
Ground ..................................... 0.3V to (V
IN
+ 0.3V)
V
OUT
Short-Circuit Duration ............................ Indefinite
I
OUT
...................................................................... 90mA
Operating Temperature Range
Commercial ............................................ 0
°
C to 70
°
C
Extended Commercial (Note 2) ........... 40
°
C to 85
°
C
Industrial ........................................... 40
°
C to 85
°
C
Storage Temperature Range ................. 65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec).................. 300
°
C
Maximum Junction Temperature .......................... 125
°
C
ORDER PART
NUMBER
ORDER PART
NUMBER
LTC1682CMS8
LTC1682CMS8-3.3
LTC1682CMS8-5
LTC1682IMS8
LTC1682IMS8-3.3
LTC1682IMS8-5
LTC1682CS8
LTC1682CS8-3.3
LTC1682CS8-5
LTC1682IS8
LTC1682IS8-3.3
LTC1682IS8-5
MS8 PART MARKING
LTER
LTGT
LTGV
LTHM
LTGU
LTGW
Consult factory for Military grade parts.
S8 PART MARKING
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Operating Voltage
LTC1682
q
1.8
4.4
V
LTC1682-3.3
q
2
4.4
V
LTC1682-5
q
2.7
4.4
V
I
VIN
Shutdown Current
SHDN = 0V
q
1
5
µ
A
I
VIN
Operating Current
I
OUT
= 0mA, Burst Mode
TM
Operation
0
°
C to 70
°
C
q
150
250
µ
A
40
°
C to 85
°
C
q
150
300
µ
A
FB Input Current
LTC1682, FB = 1.235V
q
50
50
nA
FB Voltage
LTC1682
q
1.210
1.235
1.260
V
Regulated Output Voltage
LTC1682-3.3, I
OUT
= 1mA
q
3.23
3.30
3.37
V
LTC1682-5, I
OUT
= 1mA
q
4.9
5.0
5.1
V
V
OUT
Temperature Coefficient
±
50
ppm
Charge Pump Oscillator Frequency
I
OUT
> 200
µ
A, V
IN
= 1.8V to 4.4V
q
480
550
620
kHz
Burst Mode is a trademark of Linear Technology Corporation.
T
JMAX
= 125
°
C,
JA
= 120
°
C/ W
T
JMAX
= 125
°
C,
JA
= 140
°
C/ W
1682I
1682I33
1682I5
1682
168233
16825
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
1
2
3
4
V
OUT
SHDN
FILT/FB*
GND
8
7
6
5
CPO
C
+
V
IN
C
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
*PIN3 = FILT FOR LTC1682-3.3/LTC1682-5
= FB FOR LTC1682
TOP VIEW
S8 PACKAGE
8-LEAD PLASTIC SO
1
2
3
4
8
7
6
5
V
OUT
SHDN
FILT/FB*
GND
CPO
C
+
V
IN
C
*PIN3 = FILT FOR LTC1682-3.3/LTC1682-5
= FB FOR LTC1682
PACKAGE/ORDER I
N
FOR
M
ATIO
N
U
U
W
ELECTRICAL CHARACTERISTICS
3
LTC1682/LTC1682-3.3/LTC1682-5
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
CPO (Charge Pump Output)
V
IN
= 1.8V, I
OUT
= 10mA
q
18
30
Output Resistance
V
IN
= 3V, I
OUT
= 10mA
q
13
20
V
IN
= 4.4V, I
OUT
= 10mA
q
11
17
V
OUT
Dropout Voltage (Note 3)
LTC1682, I
OUT
= 10mA, V
OUT
= 2.57V (Note 5)
q
100
160
mV
LTC1682/LTC1682-3.3, I
OUT
= 10mA, V
OUT
= 3.3V
q
75
120
mV
LTC1682/LTC1682-5, I
OUT
= 10mA, V
OUT
= 5V
q
50
90
mV
V
OUT
Enable Time
I
OUT
= 10mA
2
ms
V
OUT
Output Noise Voltage
LTC1682
I
OUT
= 10mA, 10Hz
f
100kHz, V
OUT
= 5V
88
µ
V
RMS
I
OUT
= 10mA, 10Hz
f
2.5MHz, V
OUT
= 5V
800
µ
V
P-P
LTC1682-3.3
I
OUT
= 10mA, 10Hz
f
100kHz, C
FILT
= 1nF
58
µ
V
RMS
I
OUT
= 10mA, 10Hz
f
2.5MHz, C
FILT
= 1nF
500
µ
V
P-P
LTC1682-5
I
OUT
= 10mA, 10Hz
f
100kHz, C
FILT
= 1nF
64
µ
V
RMS
I
OUT
= 10mA, 10Hz
f
2.5MHz, C
FILT
= 1nF
600
µ
V
P-P
V
OUT
Line Regulation
V
IN
= 3V to 4V, I
OUT
= 0mA (Note 6)
q
5
20
mV
V
OUT
Load Regulation
I
OUT
= 1mA to 10mA
q
3
10
mV
I
OUT
= 1mA to 50mA (Note 4)
10
mV
V
OUT
Shutdown Resistance
SHDN = 0V, Resistance Measured to Ground, V
IN
= 1.8V
q
150
350
SHDN = 0V, Resistance Measured to Ground, V
IN
= 4.4V
q
50
150
SHDN Input Threshold
V
IN
= 1.8V to 4.4V
q
0.4
1
1.6
V
SHDN Input Current
SHDN = V
IN
q
1
1
µ
A
SHDN = 0V
q
1
1
µ
A
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1682C is guaranteed to meet specified performance from
0
°
C to 70
°
C and is designed, characterized and expected to meet these
extended temperature limits, but is not tested at 40
°
C and 85
°
C. The
LTC1682I is guaranteed to meet the extended temperature limits.
Note 3: Dropout voltage is the minimum input/output voltage required to
maintain regulation at the specified output current. In dropout the output
voltage will be equal to: V
CPO
V
DROPOUT
(see Figure 4).
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output specification will not apply for all
possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range may be
limited. When operating at maximum output current, the input voltage
range may be limited.
Note 5: Limited by the LDO disable switch point of 1.45V
IN
.
Note 6: The LTC1682 is set to 5V. The feedback current is 25
µ
A.
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are T
A
= 25
°
C. SHDN = V
IN
= 3V; C1 = 0.22
µ
F; C2, C3, C4 = 4.7
µ
F, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
4
LTC1682/LTC1682-3.3/LTC1682-5
Oscillator Frequency vs
Temperature
Operating Current vs V
IN
(No Load)
V
OUT
Transient Response
V
OUT
200
µ
V/DIV
100
µ
s/DIV
1682 G04
C
CPO
= C
OUT
= 4.7
µ
F
V
OUT
= 5V
I
OUT
= 10mA
T
A
= 25
°
C
V
IN
= 3V
C
FILT
= 1nF
LTC1682-5 Output Noise
(BW = 10Hz to 2.5MHz)
Shutdown to Enable Timing
Min and Max V
CPO
vs V
IN
CPO Output Resistance vs V
IN
Enable to Shutdown Timing
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
V
IN
(V)
1.5
R
CPO
(
)
35
30
25
20
15
10
5
2.0
2.5
3.0
3.5
1682 G01
4.0
4.5
T
A
= 25
°
C
C1 = 0.22
µ
F
I
OUT
= 10mA
V
IN
(V)
1.5
V
CPO
(V)
9
8
7
6
5
4
3
2.0
2.5
3.0
3.5
1682 G02
4.0
4.5
V
CPO
= 2(V
IN
)
(A)
(A) THE MAXIMUM GENERATED NO LOAD
CPO VOLTAGE
(B) THE MINIMUM ALLOWABLE CPO VOLTAGE,
AT FULL LOAD, TO ENSURE THAT THE LDO
IS NOT DISABLED
(B)
V
CPO
= 1.45(V
IN
)
T
A
= 25
°
C
TIME (
µ
s)
0
50
V
OUT
(mV)
I
OUT
(mA)
100
200
150
250
300
1682 G02
10
5
0
5
10
15
10
5
0
T
A
= 25
°
C
V
IN
= 3V
V
OUT
= 4V
C
OUT
= 10
µ
F
200
µ
s/DIV
SHDN (V)
V
OUT
(V)
2
0
4
3
2
1
0
1682 G05
T
A
= 25
°
C
V
IN
= 3V
V
OUT
= 4V
I
OUT
= 10mA
C
CPO
= C
OUT
= 10
µ
F
1ms/DIV
SHDN (V)
V
OUT
(V)
2
0
4
3
2
1
0
1682 G06
NO LOAD
T
A
= 25
°
C
V
IN
= 3V
V
OUT
= 4V
C
OUT
= 10
µ
F
TEMPERATURE (
°
C)
50
565
560
555
550
545
540
535
530
25
75
1682 G07
25
0
50
100
125
OSCILLATION FREQUENCY (kHz)
V
IN
= 3V
V
IN
(V)
OPERATING CURRENT (
µ
A)
220
200
180
160
140
120
100
80
60
1682 G08
1.5
2.0
2.5
3.0
3.5
4.0
4.5
T
A
= 25
°
C
LTC1682-3.3
LTC1682-5
LTC1682
5
LTC1682/LTC1682-3.3/LTC1682-5
V
OUT
(Pin 1): Low Noise Regulated Output Voltage. V
OUT
should be bypassed with a
2
µ
F low ESR capacitor as
close to the pin as possible for best performance. The V
OUT
range is 2.5V to 5.5V.
SHDN (Pin 2): Shutdown Input. A logic low on the SHDN
pin puts the part in shutdown mode. A logic high enables
the part. To continuously enable the part connect SHDN to
V
IN
. When the part is in shutdown, V
OUT
will be connected
to ground via a 100
switch and CPO will be high
impedance disconnected from V
IN
.
FB (Pin 3) (LTC1682): The voltage on this pin is compared
to the internal reference voltage (1.235V) by the error
amplifier to keep the output in regulation. An external
resistor divider is required between V
OUT
and FB to adjust
the output voltage.
FILT (Pin 3) (LTC1682-3.3/LTC1682-5): This pin is used
to filter the internal voltage reference. Typically a 1nF
capacitor is connected from FILT to ground.
GND (Pin 4): System Ground.
C
(Pin 5): Flying Capacitor Negative Input.
V
IN
(Pin 6): Input Voltage, 1.8V to 4.4V. V
IN
should be
bypassed with a
2
µ
F low ESR capacitor as close to the
pin as possible for best performance. A minimum capaci-
tance value of 0.1
µ
F is required.
C
+
(Pin 7): Flying Capacitor Positive Input.
CPO (Pin 8): Unregulated Charge Pump Output Voltage.
Approximately 1.95(V
IN
) at low loads. Bypass with a
2
µ
F
low ESR capacitor. If a minimum V
OUT
enable time is
required, the CPO capacitor should be 2
×
the V
OUT
capacitor.
PI
N
FU
N
CTIO
N
S
U
U
U
TEMPERATURE (
°
C)
50
V
OUT
VOLTAGE (V)
5.030
5.020
5.010
5.000
4.990
3.340
3.330
3.320
3.310
3.300
3.290
1.238
1.240
1.236
1.234
1682 G09
25
25
50
125
0
75
100
LTC1682
LTC1682-3.3
LTC1682-5
V
IN
= 3V
I
OUT
= 10mA
V
OUT
Voltage vs Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
OUTPUT CURRENT (mA)
0
V
OUT
VOLTAGE (V)
4.994
4.993
3.300
4.997
4.996
4.995
5.000
4.999
4.998
15
25
40 45 50
1682 G10
3.299
3.298
3.297
3.296
3.295
3.294
5
10
20
30 35
V
IN
= 3.3V
T
A
= 25
°
C
LTC1682-5
LTC1682-3.3
V
OUT
Voltage vs Output Current
6
LTC1682/LTC1682-3.3/LTC1682-5
Figure 1. LTC1682 Block Diagram
BLOCK DIAGRA S
M
W
+
+
+
CHARGE PUMP
AND
SLEW CONTROL
550kHz
OSCILLATOR
POWER-
ON
RESET
SD
REGEN
ENB
REGEN
FB
CLK1
REG B
SHDN
C1
0.22
µ
F
C
+
V
IN
V
IN
V
REF
= 1.235V
C
275k
C3
4.7
µ
F
38k
328k
1:100
1
µ
A/2
µ
A
SD
LDO
100
ENB
GND
CPO
V
OUT
1682 F01
C2
4.7
µ
F
R1
R2
C4
4.7
µ
F
8
5
7
6
2
3
4
1
7
LTC1682/LTC1682-3.3/LTC1682-5
+
+
+
CHARGE PUMP
AND
SLEW CONTROL
550kHz
OSCILLATOR
POWER-
ON
RESET
SD
FILT
REGEN
ENB
REGEN
CLK1
REG B
SHDN
C1
0.22
µ
F
C
+
V
IN
V
IN
200k
RB
200k
RA
120k/65.5k
V
REF
= 1.235V
C
275k
C3
4.7
µ
F
1nF
38k
328k
1:100
1
µ
A/2
µ
A
SD
100
ENB
GND
CPO
V
OUT
1682 F02
C2
4.7
µ
F
C4
4.7
µ
F
8
5
7
6
2
3
4
1
LDO
Figure 2. LTC1682-3.3/LTC1682-5 Block Diagram
BLOCK DIAGRA S
M
W
8
LTC1682/LTC1682-3.3/LTC1682-5
Operation
The LTC1682 uses a switched-capacitor charge pump to
generate a CPO voltage of approximately 2(V
IN
). CPO
powers an internal low dropout linear regulator that sup-
plies a regulated output at V
OUT
. Internal comparators are
used to sense CPO and V
IN
voltages for power-up condi-
tioning. The output current is sensed to determine the
charge pump operating mode. A trimmed internal bandgap
is used as the voltage reference and a trimmed internal
oscillator is used to control the charge pump switches.
The charge pump is a doubler configuration that uses one
external flying capacitor. When enabled, a 2-phase
nonoverlapping clock controls the charge pump switches.
At start-up, the LDO is disabled and the load is removed
from CPO. When CPO reaches 1.75(V
IN
) the LDO is
enabled. If CPO falls below 1.45(V
IN
) the LDO will be
disabled. Generally, the charge pump runs open loop with
continuous clocking for low noise. If CPO is greater than
1.95(V
IN
)
and I
OUT
is less than 100
µ
A, the charge pump
will operate in Burst Mode operation for increased effi-
ciency but slightly higher output noise. In Burst Mode
operation, the clock is disabled when CPO reaches 1.95(V
IN
)
and enabled when CPO droops by about 100mV. The
switching frequency is precisely controlled to ensure that
the frequency is above 455kHz and at the optimum rate to
ensure maximum efficiency. The switch edge rates are
also controlled to minimize noise. The effective output
resistance at CPO is dependent on the voltage at V
IN
, CPO
and the junction temperature. A low ESR capacitor of
2
µ
F
should be used at CPO for minimum noise.
The LDO is used to filter the ripple on CPO and to set an
output voltage independent of CPO. V
OUT
is set by an
external or internal resistor divider. The LDO requires a
capacitor on V
OUT
for stability and improved load transient
response. A low ESR capacitor of
2
µ
F should be used.
Output Voltage Selection
The LTC1682-3.3/LTC1682-5 versions have internal
resistor networks to set the regulated output voltage. The
LTC1682 output voltage is set using an external resistor
divider (see Figure 3). The output voltage is determined
using the following formula:
V
OUT
= 1.235V(1 + R1/R2)
The output voltage range is 2.5V to 5.5V.
Maximum V
OUT
and I
OUT
Calculations
The maximum available output voltage and current can be
calculated based on the open circuit CPO voltage, the
dropout voltage of the LDO and the effective output
resistance of the charge pump. The open circuit CPO
voltage is approximately 2(V
IN
) (see Figure 4).
Figure 3. Powering an Auxiliary Regulator from CPO
APPLICATIO
N
S I
N
FOR
M
ATIO
N
W
U
U
U
R1
56k
R2
18k
C1
0.22
µ
F
C4
4.7
µ
F
1682 F03
V
IN
3.6V
C3
4.7
µ
F
5.1V
V
RIPPLE
= 800
µ
V
P-P
1
2
3
4
8
7
6
5
V
OUT
SHDN
FB
GND
CPO
C
+
V
IN
C
LTC1682
C2
4.7
µ
F
IN
3.3V
OUT
GND
C5
EXTERNAL LDO
V
OUT
= 1.235V(1 + R1/R2)
+
2V
IN
R
CPO
C
CPO
V
CPO
V
OUT
I
LOAD
1682 F04
R
DROPOUT
V
DROPOUT
+
Figure 4. Equivalent Circuit
9
LTC1682/LTC1682-3.3/LTC1682-5
The following formula can be used to find the maximum
output voltage that may be programmed for a given
minimum input voltage and output current load:
V
OUT(MAX)
= (2)(V
IN(MIN)
) (I
OUT
)(R
CPO
) V
DROPOUT
with the condition that (I
OUT
)(R
CPO
) < 0.55V
IN
.
Example:
V
IN(MIN)
= 3V
I
OUT
= 10mA
R
CPO(MAX)
= 20
Max unloaded CPO voltage = 6V
Loaded CPO voltage = 6V (10mA)(20
) = 5.8V
V
DROPOUT(MAX)
= 0.08V
V
OUT(MAX)
= (6V) (0.2V) (0.08V) = 5.72V
V
OUT
< 5.5V and (I
OUT
)(R
CPO
) < 0.55V
IN
, 0.2V < 1.65V.
For minimum noise applications, the LDO must be kept out
of dropout to prevent CPO noise from coupling into V
OUT
.
External CPO Loading
The CPO output can drive an external load (an LDO, for
example). The current required by this additional load will
reduce the available current from V
OUT
. If the external load
requires 5mA, then the maximum available current at V
OUT
will be reduced by 5mA.
Short-Circuit and Thermal Protection
V
OUT
can be shorted to ground indefinitely. Internal cir-
cuitry will limit the output current. If the junction tempera-
ture exceeds 150
°
C, the part will shut down. Excessive
power dissipation due to heavy loads will also cause the
part to shut down when the junction temperature exceeds
150
°
C. The part will become enabled when the junction
temperature drops below 140
°
C. If the fault condition
remains in place, the part will cycle between the shutdown
and enabled states.
Capacitor Selection
For best performance it is recommended that low ESR
capacitors be used for C2, C3 and C4 in Figure 1 to
reduce noise and ripple. C2 must be
2
µ
F and C3 must
be equal to or greater than C2. C4 is dependent on the
source impedance. The charge pump demands large
APPLICATIO
N
S I
N
FOR
M
ATIO
N
W
U
U
U
instantaneous currents which may induce ripple onto
a common voltage rail. C4 should be
2
µ
F and a spike
reducing resistor of 2.2
may be required between
V
IN
and the supply.
A low ESR ceramic capacitor is recommended for the
flying capacitor C1 with a value of 0.22
µ
F. At low load or
high V
IN
a smaller capacitor could be used to reduce ripple
on CPO which would reflect as lower ripple on V
OUT
.
If a minimum enable time is required, the CPO output filter
capacitor should be at least 2
×
the V
OUT
filter capacitor.
When the LDO is first enabled, the CPO capacitor will
dump a large amount of charge into the V
OUT
capacitor. If
the drop in the CPO voltage falls below 1.45(V
IN
), the LDO
will be disabled and the CPO voltage will have to charge up
to 1.75(V
IN
) to enable the LDO. The resulting cycling
extends the enable time.
A 1nF filter capacitor for the LTC1682-3.3/LTC1682-5
should be connected between the FILT pin and ground for
optimum noise performance.
Output Ripple
The output noise and ripple on CPO includes a spike
component from the charge pump switches and a droop
component which is dependent on the load current and the
value of C3. The charge pump has been carefully designed
to minimize the spike component; however, low ESR
capacitors are essential to reduce the remaining spike
energy effect on the CPO voltage. C3 should be increased
for high load currents to minimize the droop component.
Ripple components on CPO are greatly reduced at V
OUT
by
the LDO; however, C2 should also be a low ESR capacitor
to improve filtering of the CPO noise.
Shutdown
When SHDN pin is pulled low (< 0.4V), the part will be in
shutdown, the supply current will be < 5
µ
A and V
OUT
will
be connected to ground through a 100
switch. In addi-
tion, CPO will be high impedance and disconnected from
V
IN
.
If shutdown is not required, connect SHDN to V
IN
which
will continuously enable the part.
10
LTC1682/LTC1682-3.3/LTC1682-5
APPLICATIO
N
S I
N
FOR
M
ATIO
N
W
U
U
U
General Layout Considerations
Due to the high switching frequency and high transient
currents produced by the device, careful board layout is a
must. A clean board layout using a ground plane and short
connections to all capacitors will improve noise perfor-
mance and ensure proper regulation (Figure 5).
The FILT pin on the LTC1682-3.3/LTC1682-5 is a high
impedance node. Leakage currents at this pin must be
minimized.
Measuring Output Noise
Measuring the LTC1682 low noise levels requires care.
Figure 6 shows a test setup for taking the measurement.
Good connection and signal handling technique should
yield about 500
µ
V
P-P
over a 2.5MHz bandwidth. The noise
measurement involves AC coupling the LTC1682 output
into the test setup's input and terminating this connection
with 50
. Coaxial connections must be maintained to
preserve measurement integrity.
Power-On Reset
Upon initial power-up, a power-on reset circuit ensures
that the internal functions are correctly initialized when
power is applied. Once V
IN
reaches approximately 1V, the
power-on reset circuit will enable the part as long as the
SHDN pin is held high.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125
°
C). The
device power dissipation P
D
= I
OUT
(2V
IN
V
OUT
) +
V
IN
(4mA). The device dissipates the majority of its heat
through its pins, especially GND (Pin 4). Thermal resis-
tance to ambient can be optimized by connecting GND to
a large copper region on the PCB, which serves as a heat
sink. Applications which operate the LTC1682 near maxi-
mum power levels should maximize the copper area at all
pins except C
+
, C
and FILT/FB and ensure that there is
some airflow over the part to carry away excess heat.
1
2
3
4
LTC1682-3.3/5
8
7
6
5
C1
V
OUT
V
IN
1682 F05
C3
C2
GND
SHDN
C4
C
FILT
LTC1682
DEMO
BOARD
OSCILLOSCOPE
BANDWIDTH
FILTER
CONNECT BNC AND
R
LOAD
GROUND TO THE
OUTPUT CAPACITOR
GROUND TERMINAL E5
PLACE COUPLING
CAPACITOR IN SHIELDED
BOX WITH COAXIAL
CONNECTOR
COUPLING
CAPACITOR
BNC CABLES
OR COUPLERS
BATTERY OR
LOW NOISE DC
POWER SUPPLY
V
OUT
R
LOAD
R*
R*
*50
TERMINATIONS
HP-11048C OR
EQUIVALENT
R*
NOTE: KEEP BNC CONNECTIONS
AS SHORT AS POSSIBLE
PLACE BANDWIDTH FILTER
COMPONENTS IN SHIELDED BOX
WITH COAXIAL CONNECTORS
PREAMPLIFIER
1822
INPUT
1682 F06
+
20dB
Figure 6. LTC1682 Noise Measurement Test Setup
Figure 5
11
LTC1682/LTC1682-3.3/LTC1682-5
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTIO
N
U
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
TYPICAL APPLICATIO
N
U
C1
0.22
µ
F
C
FILT
1nF
1682 TA03
V
IN
3.3V
C2
4.7
µ
F
3.3V
1
2
SHUTDOWN
3
4
8
7
6
5
V
OUT
SHDN
FILT
GND
CPO
C
+
V
IN
C
LTC1682-3.3
C3
4.7
µ
F
C4
4.7
µ
F
V
RIPPLE
= 500
µ
V
P-P
3.3V to Low Noise 3.3V Converter
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
MSOP (MS8) 1197
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.021
±
0.006
(0.53
±
0.015)
0
°
6
°
TYP
SEATING
PLANE
0.007
(0.18)
0.040
±
0.006
(1.02
±
0.15)
0.012
(0.30)
REF
0.006
±
0.004
(0.15
±
0.102)
0.034
±
0.004
(0.86
±
0.102)
0.0256
(0.65)
TYP
1
2
3
4
0.192
±
0.004
(4.88
±
0.10)
8
7 6
5
0.118
±
0.004*
(3.00
±
0.102)
0.118
±
0.004**
(3.00
±
0.102)
1
2
3
4
0.150 0.157**
(3.810 3.988)
8
7
6
5
0.189 0.197*
(4.801 5.004)
0.228 0.244
(5.791 6.197)
0.016 0.050
0.406 1.270
0.010 0.020
(0.254 0.508)
×
45
°
0
°
8
°
TYP
0.008 0.010
(0.203 0.254)
SO8 0996
0.053 0.069
(1.346 1.752)
0.014 0.019
(0.355 0.483)
0.004 0.010
(0.101 0.254)
0.050
(1.270)
TYP
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
12
LTC1682/LTC1682-3.3/LTC1682-5
128235fs, sn128235 LT/TP 0799 4K · PRINTED IN USA
©
LINEAR TECHNOLOGY CORPORATION 1999
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear-tech.com
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TYPICAL APPLICATIO
N
U
Wide Input Range VCO Supply (V
IN
> 4.4V)
SHUTDOWN
C1
0.22
µ
F
C4
4.7
µ
F
3V
(REQUIRED FOR
START-UP)
Q1
FMMT3904
1682 ta04
V
IN
3V TO 6V
C3
4.7
µ
F
5V
LOW NOISE
1
2
3
4
8
7
6
5
V
OUT
SHDN
FILT
GND
CPO
C
+
V
IN
C
R1
470
LTC1682-5
C2
4.7
µ
F
C
FILT
1nF
D1
1N4148
VCO
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