FEATURES
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LTC3736-2
Dual 2-Phase, No R
SENSE
,
Synchronous Controller
with Output Tracking
DESCRIPTION
TM
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
= 9μA
Tiny Low Profile (4mm
×
4mm) QFN and Narrow
SSOP Packages
The LTC
®
3736-2 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives
external complementary power MOSFETs using few ex-
ternal components. The constant-frequency current mode
architecture 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 minimized
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
capacitors. 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 and 24-lead narrow SSOP packages.
, LT, LTC and LTM 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.
APPLICATIONS
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One or Two Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V
IN
2.75V TO 9.8V
V
IN
SENSE1
+
TG1
2.2μH
SW1
BG1
V
OUT1
2.5V
187k
PGND
V
FB1
220pF
59k
15k
I
TH1
SGND
SW2
LTC3736-2
BG2
PGND
V
FB2
I
TH2
220pF
15k
59k
37362 TA01a
Efficiency and Power Loss
vs Load Current (Figure 15 Circuit)
100
95
90
V
OUT
= 2.5V
10
SENSE2
+
10μF
2
TG2
2.2μH
EFFICIENCY (%)
85
80
75
70
65
60
55
EFFICIENCY
1
POWER LOSS (W)
0.1
POWER LOSS
118k
V
OUT2
1.8V
47μF
0.01
47μF
50
1
10
100
1000
LOAD CURRENT (mA)
0.001
10000
37362 TA01b
37362fb
1
LTC3736-2
ABSOLUTE MAXIMUM RATINGS
(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 (<10μs) .... 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
Lead Temperature (Soldering, 10 sec)
(LTC3736EGN-2) ................................................... 300°C
PIN CONFIGURATION
TOP VIEW
V
FB1
SW1
IPRG1
V
FB1
I
TH1
IPRG2
PLLLPF
SGND
V
IN
TRACK
1
2
3
4
5
6
7
8
9
IPRG1
24 SENSE1
+
23 PGND
22 BG1
21 SYNC/FCB
20 TG1
19 PGND
18 TG2
17 RUN/SS
16 BG2
15 PGND
14 SENSE2
+
13 SW2
I
TH1
1
IPRG2 2
PLLLPF 3
SGND 4
V
IN
5
TRACK 6
7
V
FB2
8
I
TH2
9 10 11 12
SENSE2
+
PGOOD
SW2
PGND
25
TOP VIEW
SENSE1
+
PGND
SW1
BG1
18 SYNC/FCB
17 TG1
16 PGND
15 TG2
14 RUN/SS
13 BG2
24 23 22 21 20 19
V
FB2
10
I
TH2
11
PGOOD 12
GN PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3736-2EGN#PBF
LTC3736-2EUF#PBF
TAPE AND REEL
LTC3736-2EGN#TRPBF
LTC3736-2EUF#TRPBF
37362
PART MARKING
PACKAGE DESCRIPTION
24-Lead Plastic SSOP
24-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
37362fb
2
LTC3736-2
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
Shutdown Threshold at RUN/SS
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB1,2
Input Current
TRACK Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Auxiliary Feedback Threshold
Top Gate (TG) Drive 1, 2 Rise Time
Top Gate (TG) Drive 1, 2 Fall Time
Bottom Gate (BG) Drive 1, 2 Rise Time
Bottom Gate (BG) Drive 1, 2 Fall Time
Maximum Current Sense Voltage (ΔV
SENSE(MAX)
)
(SENSE
+
– SW)
Soft-Start Time
Oscillator and Phase-Locked Loop
Oscillator Frequency
Unsynchronized (SYNC/FCB Not Clocked)
PLLLPF = Floating
PLLLPF = 0V
PLLLPF = V
IN
SYNC/FCB Clocked
Minimum Synchronizable Frequency
Maximum Synchronizable Frequency
f
OSC
> f
SYNC/FCB
f
OSC
< f
SYNC/FCB
I
PGOOD
Sinking 1mA
V
FB
with Respect to Set Output Voltage
V
FB
< 0.6V, Ramping Positive
V
FB
< 0.6V, Ramping Negative
V
FB
< 0.6V, Ramping Negative
V
FB
< 0.6V, Ramping Positive
–13
–16
7
10
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise specified.
CONDITIONS
(Note 4)
RUN/SS = V
IN
RUN/SS = 0V
V
IN
= UVLO Threshold –200mV
V
IN
Falling
V
IN
Rising
RUN/SS = 0V
0°C to 85°C (Note 5)
–40°C to 85°C
2.75V < V
IN
< 9.8V (Note 5)
I
TH
= 0.9V (Note 5)
I
TH
= 1.7V
(Note 5)
TRACK = 0.6V
Measured at V
FB
SYNC/FCB Ramping Positive
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
IPRG = Floating
IPRG = 0V
IPRG = V
IN
Time for V
FB1
to Ramp from 0.05V to 0.55V
l
l
l
l
l
l
MIN
TYP
MAX
UNITS
4.75
9
3
1.95
2.15
0.45
0.4
0.594
0.591
2.25
2.45
0.65
0.7
0.6
0.6
0.05
0.12
–0.12
10
10
0.66
0.525
0.68
20
0.6
40
40
50
40
220
150
320
0.667
240
167
345
0.833
750
20
10
2.55
2.75
0.85
1
0.606
0.609
0.2
0.5
–0.5
50
50
0.7
0.675
μA
μA
μA
V
V
V
μA
V
V
mV/ V
%
%
nA
nA
V
mV
V
ns
ns
ns
ns
260
185
370
1
mV
mV
mV
ms
480
260
650
550
300
750
200
1150
–4
4
125
–10
–13.3
10
13.3
600
340
825
250
kHz
kHz
kHz
kHz
kHz
μA
μA
mV
Phase-Locked Loop Lock Range
850
Phase Detector Output Current
Sinking
Sourcing
PGOOD Output
PGOOD Voltage Low
PGOOD Trip Level
–7
–10
13
16
%
%
%
%
37362fb
3
LTC3736-2
ELECTRICAL CHARACTERISTICS
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3736E-2 is guaranteed to meet specified performance
from 0°C to 85°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
•
θ
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency and Power Loss
vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
V
IN
= 3.3V
V
IN
= 5V
10
100
1000
LOAD CURRENT (mA)
0.01
V
IN
= 3.3V
100μs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
POWER LOSS
0.1
V
OUT
= 2.5V
10
V
OUT
AC
COUPLED
100mV/
DIV
T
A
= 25°C, unless otherwise noted.
Load Step
(Forced Continuous Mode)
V
OUT
AC
COUPLED
100mV/
DIV
Load Step (Pulse-Skipping Mode)
EFFICIENCY
1
POWER LOSS (W)
I
L
2A/DIV
I
L
2A/DIV
37362 G02
0.001
10000
100μs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = V
IN
FIGURE 15 CIRCUIT
37362 G03
37362 G01
Light Load
(Pulse-Skipping Mode)
Light Load
(Forced Continuous Mode)
Tracking Start-Up with Internal
Soft-Start (C
SS
= 0μF)
V
OUT1
2.5V
SW
5V/DIV
V
OUT
50mV/DIV
AC
COUPLED
I
L
2A/DIV
V
IN
= 5V
2.5μs/DIV
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FBC = V
IN
FIGURE 15 CIRCUIT
37362 G04
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
2A/DIV
500mV/
DIV
V
OUT2
1.8V
2.5μs/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
37362 G05
V
IN
= 5V
200μs/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
37362 G06
37362fb
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LTC3736-2
TYPICAL PERFORMANCE CHARACTERISTICS
Tracking Start-Up with External
Soft-Start (C
SS
= 0.10μF)
5
NORMALIZED FREQUENCY SHIFT (%)
V
OUT1
2.5V
4
3
2
1
0
–1
–2
–3
–4
–5
2
3
4
8
6
5
7
INPUT VOLTAGE (V)
9
–20
10
0.5
1
1.5
I
TH
VOLTAGE (V)
2
37362 G09
T
A
= 25°C, unless otherwise noted.
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
100
80
CURRENT LIMIT (%)
60
40
20
0
FORCED CONTINUOUS
MODE
PULSE-SKIPPING
MODE
Oscillator Frequency
vs Input Voltage
500mV/
DIV
V
OUT2
1.8V
V
IN
= 5V
40ms/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
37362 G07
37368 G08
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
10
100
1000
LOAD CURRENT (mA)
10000
37362 G10
Regulated Feedback Voltage
vs Temperature
0.606
0.605
0.604
FEEDBACK VOLTAGE (V)
RUN/SS VOLTAGE (V)
0.603
0.602
0.601
0.600
0.599
0.598
0.597
0.596
0.595
0.594
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Shutdown (RUN) Threshold
vs Temperature
FIGURE 15 CIRCUIT
V
IN
= 3.3V
V
OUT
= 2.5V
PULSE-SKIPPING
MODE
(SYNC/FCB = V
IN
)
FORCED
CONTINUOUS
(SYNC/FCB = 0V)
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
37362 G11
37362 G12
RUN/SS Pull-Up Current
vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
1.0
RUN/SS PULL-UP CURRENT (μA)
0.9
0.8
0.7
0.6
0.5
0.4
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
180
175
170
165
160
155
Maximum Current Sense Threshold
vs Temperature
I
PRG
= GND
NROMALIZED FREQUENCY (%)
10
8
6
4
2
0
–2
–4
–6
–8
150
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
Oscillator Frequency
vs Temperature
80
100
–10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
37362 G13
37362 G14
37362 G15
37362fb
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