37362f.pm65
1
LTC3736-2
37362f
Dual 2-Phase, No R
SENSE
TM
,
Synchronous Controller
with Output Tracking
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required
Input Capacitance
Tracking Function
Wide V
IN
Range: 2.75V to 9.8V
0.6V
±1% Voltage Reference
High Current Limit
Constant Frequency Current Mode Operation
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
Selectable Pulse Skipping/Forced Continuous
Operation
Auxiliary Winding Regulation
Internal Soft-Start Circuitry
Power Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9
µA
Tiny Low Profile (4mm
× 4mm) QFN Package
The LTC
®
3736-2 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives ex-
ternal complementary power MOSFETs using few external
components. The constant frequency current mode archi-
tecture with MOSFET V
DS
sensing eliminates the need for
sense resistors and improves efficiency. Power loss and
noise due to the ESR of the input capacitance are mini-
mized by operating the two controllers out of phase.
Pulse skipping operation provides high efficiency at light
loads. 100% duty cycle capability provides low dropout
operation, extending operating time in battery-powered
systems.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and ca-
pacitors. For noise sensitive applications, the LTC3736-2
switching frequency can be externally synchronized from
250kHz to 850kHz. An internal soft-start, which can be
lengthened externally, smoothly ramps the output voltage
during start-up.
The LTC3736-2 is available in the tiny thermally enhanced
(4mm
× 4mm) QFN package.
One or Two Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
SENSE1
+
V
IN
LTC3736-2
SGND
SENSE2
+
TG1
TG2
SW1
SW2
BG1
BG2
PGND
PGND
V
FB1
V
FB2
220pF
V
OUT1
2.5V
V
OUT2
1.8V
47
µF
47
µF
15k
220pF
15k
59k
59k
187k
118k
2.2
µH
2.2
µH
I
TH1
37362 TA01a
I
TH2
10
µF
×2
V
IN
2.75V TO 9.8V
Efficiency and Power Loss
vs Load Current (Figure 15 Circuit)
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466.
LOAD CURRENT (mA)
65
EFFICIENCY (%)
POWER LOSS (W)
95
100
60
55
90
75
85
80
70
1
100
1000
10000
37362 TA01b
50
10
0.01
0.1
1
0.001
10
V
OUT
= 2.5V
EFFICIENCY
POWER LOSS
2
LTC3736-2
37362f
(Note 1)
Input Supply Voltage (V
IN
) ........................ 0.3V to 10V
PLLLPF, RUN/SS, SYNC/FCB,
TRACK, SENSE1
+
, SENSE2
+
,
IPRG1, IPRG2 Voltages ................. 0.3V to (V
IN
+ 0.3V)
V
FB1
, V
FB2
, I
TH1
, I
TH2
Voltages .................. 0.3V to 2.4V
SW1, SW2 Voltages ............ 2V to V
IN
+ 1V or 10V Max
PGOOD ..................................................... 0.3V to 10V
TG1, TG2, BG1, BG2 Peak Output Current (<10
µs) ..... 1A
Operating Temperature Range (Note 2) ... 40
°C to 85°C
Storage Temperature Range .................. 65
°C to 125°C
Junction Temperature (Note 3) ............................ 125
°C
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
24 23 22 21 20 19
7
8
9
TOP VIEW
25
UF PACKAGE
24-LEAD (4mm
× 4mm) PLASTIC QFN
10 11 12
6
5
4
3
2
1
13
14
15
16
17
18
I
TH1
IPRG2
PLLLPF
SGND
V
IN
TRACK
SYNC/FCB
TG1
PGND
TG2
RUN/SS
BG2
V
FB1
IPRG1
SW1
SENSE1
+
PGND
BG1
V
FB2
I
TH2
PGOOD
SW2
SENSE2
+
PGND
T
JMAX
= 125
°C,
JA
= 37
°C/W
EXPOSED PAD (PIN 25) IS PGND MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25
°C. V
IN
= 4.2V unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Main Control Loops
Input DC Supply Current
(Note 4)
Normal Mode
RUN/SS = V
IN
475
750
µA
Shutdown
RUN/SS = 0V
9
20
µA
UVLO
V
IN
= UVLO Threshold 200mV
3
10
µA
Undervoltage Lockout Threshold
V
IN
Falling
1.95
2.25
2.55
V
V
IN
Rising
2.15
2.45
2.75
V
Shutdown Threshold at RUN/SS
0.45
0.65
0.85
V
Start-Up Current Source
RUN/SS = 0V
0.4
0.7
1
µA
Regulated Feedback Voltage
(Note 5)
0.594
0.6
0.606
V
Output Voltage Line Regulation
2.75V < V
IN
< 9.8V (Note 5)
0.05
0.2
mV/V
Output Voltage Load Regulation
I
TH
= 0.9V (Note 5)
0.12
0.5
%
I
TH
= 1.7V
0.12
0.5
%
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
ORDER PART NUMBER
UF PART MARKING
37362
LTC3736EUF-2
3
LTC3736-2
37362f
ELECTRICAL CHARACTERISTICS
The
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25
°C. V
IN
= 4.2V unless otherwise specified.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3736E-2 is guaranteed to meet specified performance
from 0
°C to 70°C. Specifications over the 40°C to 85°C operating range
are assured by design, characterization and correlation with statistical
process controls.
Note 3: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
·
JA
°C/W)
Note 4: Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5: The LTC3736-2 is tested in a feedback loop that servos I
TH
to a
specified voltage and measures the resultant V
FB
voltage.
Note 6: Peak current sense voltage is reduced dependent on duty cycle to
a percentage of value as shown in Figure 1.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
FB1,2
Input Current
(Note 5)
10
50
nA
TRACK Input Current
TRACK = 0.6V
10
50
nA
Overvoltage Protect Threshold
Measured at V
FB
0.66
0.68
0.7
V
Overvoltage Protect Hysteresis
20
mV
Auxiliary Feedback Threshold
SYNC/FCB Ramping Positive
0.525
0.6
0.675
V
Top Gate (TG) Drive 1, 2 Rise Time
C
L
= 3000pF
40
ns
Top Gate (TG) Drive 1, 2 Fall Time
C
L
= 3000pF
40
ns
Bottom Gate (BG) Drive 1, 2 Rise Time
C
L
= 3000pF
50
ns
Bottom Gate (BG) Drive 1, 2 Fall Time
C
L
= 3000pF
40
ns
Maximum Current Sense Voltage (
V
SENSE(MAX)
)
IPRG = Floating
220
240
260
mV
(SENSE
+
SW)
IPRG = 0V
150
167
185
mV
IPRG = V
IN
320
345
370
mV
Soft-Start Time
Time for V
FB1
to Ramp from 0.05V to 0.55V
0.667
0.833
1
ms
Oscillator and Phase-Locked Loop
Oscillator Frequency
Unsynchronized (SYNC/FCB Not Clocked)
PLLLPF = Floating
480
550
600
kHz
PLLLPF = 0V
260
300
340
kHz
PLLLPF = V
IN
650
750
825
kHz
Phase-Locked Loop Lock Range
SYNC/FCB Clocked
Minimum Synchronizable Frequency
200
250
kHz
Maximum Synchronizable Frequency
850
1150
kHz
Phase Detector Output Current
Sinking
f
OSC
> f
SYNC/FCB
4
µA
Sourcing
f
OSC
< f
SYNC/FCB
4
µA
PGOOD Output
PGOOD Voltage Low
I
PGOOD
Sinking 1mA
125
mV
PGOOD Trip Level
V
FB
with Respect to Set Output Voltage
V
FB
< 0.6V, Ramping Positive
13
10.0
7
%
V
FB
< 0.6V, Ramping Negative
16
13.3
10
%
V
FB
> 0.6V, Ramping Negative
7
10.0
13
%
V
FB
> 0.6V, Ramping Positive
10
13.3
16
%
4
LTC3736-2
37362f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Efficiency and Power Loss
vs Load Current
Load Step
(Forced Continuous Mode)
Load Step (Pulse Skipping Mode)
Light Load (Pulse Skipping Mode)
Tracking Start-Up with Internal
Soft-Start (C
SS
= 0
µF)
INPUT VOLTAGE (V)
2
5
NORMALIZED FREQUENCY SHIFT (%) 4
2
1
0
5
2
4
6
7
37368 G08
3
3
4
1
3
5
8
9
10
Oscillator Frequency
vs Input Voltage
Tracking Start-Up with External
Soft-Start (C
SS
= 0.10
µF)
T
A
= 25
°C unless otherwise noted.
LOAD CURRENT (mA)
65
EFFICIENCY (%)
POWER LOSS (W)
95
100
60
55
90
75
85
80
70
1
100
1000
10000
37362 G01
50
10
0.01
0.1
1
0.001
10
V
OUT
= 2.5V
EFFICIENCY
POWER LOSS
V
IN
= 3.3V
V
IN
= 5V
V
OUT
AC-COUPLED
100mV/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
100
µs/DIV
37362 G03
I
L
2A/DIV
V
OUT
AC-COUPLED
100mV/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = V
IN
FIGURE 15 CIRCUIT
100
µs/DIV
37362 G04
I
L
2A/DIV
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
2.5
µs/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FBC = V
IN
FIGURE 15 CIRCUIT
37362 G02
I
L
2A/DIV
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
2.5
µs/DIV
37362 G05
I
L
2A/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
Light Load
(Forced Continuous Mode)
V
IN
= 5V
R
LOAD1
= R
LOAD2
= 1
FIGURE 15 CIRCUIT
200
µs/DIV
37362 G06
500mV/
DIV
V
OUT1
2.5V
V
OUT2
1.8V
V
IN
= 5V
R
LOAD1
= R
LOAD2
= 1
FIGURE 15 CIRCUIT
40ms/DIV
37362 G07
500mV/
DIV
V
OUT1
2.5V
V
OUT2
1.8V
5
LTC3736-2
37362f
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
I
TH
VOLTAGE (V)
0.5
20
CURRENT LIMIT (%)
0
20
40
60
100
1
1.5
37362 G09
2
80
FORCED CONTINUOUS
MODE
PULSE SKIPPING
MODE
LOAD CURRENT (mA)
65
EFFICIENCY (%)
95
100
60
55
90
75
85
80
70
1
100
1000
10000
37362 G10
50
10
FIGURE 15 CIRCUIT
V
IN
= 3.3V
V
OUT
= 2.5V
PULSE SKIPPING
MODE
(SYNC/FCB = V
IN
)
FORCED
CONTINUOUS
(SYNC/FCB = 0V)
Efficiency vs Load Current
Regulated Feedback Voltage
vs Temperature
Shutdown (RUN) Threshold
vs Temperature
RUN/SS Pull-Up Current
vs Temperature
Maximum Current Sense Threshold
vs Temperature
TEMPERATURE (
°C)
60
0
RUN/SS VOLTAGE (V)
0.1
0.3
0.4
0.5
1.0
0.7
20
20
40
37362 G12
0.2
0.8
0.9
0.6
40
0
60
80
100
TEMPERATURE (
°C)
60
0.4
RUN/SS PULL-UP CURRENT (
µ
A)
0.5
0.6
0.7
0.8
20
20
60
100
37362 G13
0.9
1.0
40
0
40
80
Oscillator Frequency
vs Temperature
TEMPERATURE (
°C)
60
10
NROMALIZED FREQUENCY (%)
8
4
2
0
10
4
20
20
40
37362 G15
6
6
8
2
40
0
60
80
100
TEMPERATURE (
°C)
60
INPUT (V
IN
) VOLTAGE (V) 2.30
2.40
100
37362 G16
2.20
2.10
20
20
60
40
0
40
80
2.50
2.25
2.35
2.15
2.45
V
IN
RISING
V
IN
FALLING
Undervoltage Lockout Threshold
vs Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
T
A
= 25
°C unless otherwise noted.
TEMPERATURE (
°C)
60
150
MAXIMUM CURRENT SENSE THRESHOLD (mV)
155
160
165
170
20
20
60
100
37362 G11
175
180
40
0
40
80
I
PRG
= GND
TEMPERATURE (
°C)
60
FEEDBACK VOLTAGE (V)
0.600
0.603
0.604
100
37362 G14
0.599
0.598
0.594
20
20
60
40
0
40
80
0.596
0.606
0.605
0.602
0.601
0.597
0.595
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