LTC3728
Dual, 550kHz, 2-Phase
Synchronous Step-Down
Switching Regulator
FEATURES DESCRIPTION
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Dual, 180 Phased Controllers Reduce Required
The LTC 3728 is a dual high performance step-down
Input Capacitance and Power Supply Induced Noise
switching regulator controller that drives all N-channel
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OPTI-LOOP Compensation Minimizes C
synchronous power MOSFET stages. A constant-frequency
OUT
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1% Output Voltage Accuracy
current mode architecture allows phase-lockable frequency
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Power Good Output Voltage Indicator
of up to 550kHz. Power loss and noise due to the ESR of
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Phase-Lockable Fixed Frequency 250kHz to 550kHz
the input capacitors are minimized by operating the two
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Dual N-Channel MOSFET Synchronous Drive
controller output stages out of phase.
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Wide V Range: 3.5V to 36V Operation
IN
OPTI-LOOP compensation allows the transient response to
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Very Low Dropout Operation: 99% Duty Cycle
be optimized over a wide range of output capacitance and
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Adjustable Soft-Start Current Ramping
ESR values. The precision 0.8V reference and power good
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Foldback Output Current Limiting
output indicator are compatible with future microprocessor
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Latched Short-Circuit Shutdown with Defeat Option
generations, and a wide 3.5V to 30V (36V maximum) input
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Output Overvoltage Protection
supply range encompasses all battery chemistries.
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Remote Output Voltage Sense
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A RUN/SS pin for each controller provides both soft-
Low Shutdown I : 20A
Q
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5V and 3.3V Regulators start and optional timed, short-circuit shutdown. Current
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foldback limits MOSFET dissipation during short-circuit
3 Selectable Operating Modes: Constant-Frequency,
conditions when overcurrent latchoff is disabled. Output
Burst Mode Operation and PWM
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overvoltage protection circuitry latches on the bottom
Available in 32-Pin 5mm 5mm QFN and
28-Pin SSOP Packages MOSFET until V returns to normal. The FCB mode
OUT
pin can select among Burst Mode, constant-frequency
APPLICATIONS
mode and continuous inductor current mode or regulate
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Notebook and Palmtop Computers
a secondary winding. The LTC3728 includes a power good
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Telecom Systems
output pin that indicates when both outputs are within
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Portable Instruments
7.5% of their designed set point.
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Battery-Operated Digital Devices L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and OPTI-LOOP are
registered trademarks of Linear Technology Corporation. All other trademarks are the property
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DC Power Distribution Systems
of their respective owners. Protected by U.S. Patents including 5481178, 5929620, 6177787,
6144194, 6100678, 5408150, 6580258, 5705919.
V
TYPICAL APPLICATION IN
+ C 5.2V TO 28V
IN
4.7F
1F 22F
D3
V PGOOD INTV
D4
IN CC
M1 M2 50V
TG1 TG2
L1 L2
BOOST1 BOOST2
3.2H 3.2H
C , 0.1F
C , 0.1F B2
B1
SW1 SW2
LTC3728
BG1 BG2
f
IN
PLLIN PGND
500kHz
+ +
SENSE1 SENSE2
R
R SENSE2
SENSE1
1000pF 1000pF
0.01
0.01
SENSE1 SENSE2
V
V V V OUT2
OUT1 OSENSE1 OSENSE2
R2 R4
3.3V
5V
I I
TH1 TH2
105k 63.4k
C C C C
5A OUT1 C1 C2 OUT 5A
RUN/SS1 SGND RUN/SS2
+ R1 R3
47F 1% 220pF 220pF 1% 56F
20k R C C 20k 6V
6V C1
SS1 SS2 R
C2
1% 15k 1%
SP 0.1F 0.1F SP
15k
M1, M2: FDS6982S
3728 F01
Figure 1. High Ef ciency Dual 5V/3.3V Step-Down Converter
3728fg
1
+LTC3728
ABSOLUTE MAXIMUM RATINGS (Note 1)
I I , V , V Voltages ... 2.7V to 0.3V
Input Supply Voltage (V ) .........................36V to 0.3V
TH1, TH2 OSENSE1 OSENSE2
IN
Peak Output Current <10s (TG1, TG2, BG1, BG2) .....3A
Topside Driver Voltages
INTV Peak Output Current ................................. 50mA
(BOOST1, BOOST2) ............................... 42V to 0.3V
CC
Operating Temperature Range (Note 7).... 40C to 85C
Switch Voltage (SW1, SW2) ......................... 36V to 5V
Junction Temperature (Note 2) ............................. 125C
INTV EXTV , RUN/SS1, RUN/SS2,
CC, CC
Storage Temperature Range ................... 65C to 125C
(BOOST1-SW1), (BOOST2-SW2), PGOOD ..... 7V to 0.3V
+ +
Lead Temperature (Soldering, 10 sec)
SENSE1 , SENSE2 , SENSE1 ,
(G Package Only) .................................................. 300C
SENSE2 Voltages .........................(1.1)INTV to 0.3V
CC
PLLIN, PLLFLTR, FCB Voltages ............ INTV to 0.3V
CC
PIN CONFIGURATION
TOP VIEW TOP VIEW
RUN/SS1 1 28 PGOOD
+
2 TG1
SENSE1 27
32 31 30 29 28 27 26 25
SENSE1 3 26 SW1
V 1 24 BOOST1
4 25 BOOST1 OSENSE1
V
OSENSE1
PLLFLTR 2 23 V
IN
PLLFLTR 5 24 V
IN
PLLIN 3 22 BG1
PLLIN 6 23 BG1
FCB 4 21 EXTV
CC
7 EXTV
FCB 22
CC 33
I 5 20 INTV
TH1 CC
I 8 21 INTV
TH1 CC
SGND 6 19 PGND
9 20 PGND
SGND
3.3V 7 18 BG2
OUT
3.3V 10 19 BG2
OUT
I 8 17 BOOST2
TH2
I 11 18 BOOST2
TH2
9 10 11 12 13 14 15 16
12 SW2
V 17
OSENSE2
SENSE2 13 16 TG2
+
14 15 RUN/SS2
SENSE2
G PACKAGE UH PACKAGE
28-LEAD PLASTIC SSOP 32-LEAD (5mm 5mm) PLASTIC QFN
T = 125C, = 90C/W - SINGLE LAYER BOARD T = 125C, = 34C/W
JMAX JA JMAX JA
68 C/W - 4 LAYER EXPOSED PAD IS SGND (MUST BE SOLDERED TO PCB)
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3728EG#PBF LTC3728EG#TRPBF LTC3728EG 28-Lead Plastic SSOP 40C to 85C
LTC3728IG#PBF LTC3728IG#TRPBF LTC3728IG 28-Lead Plastic SSOP 40C to 85C
LTC3728EUH#PBF LTC3728EUH#TRPBF 3728 32-Lead (5mm 5mm) Plastic QFN 40C to 85C
LTC3728IUH#PBF LTC3728IUH#TRPBF 3728 32-Lead (5mm 5mm) Plastic QFN 40C to 85C
LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3728EG LTC3728EG#TR LTC3728EG 28-Lead Plastic SSOP 40C to 85C
LTC3728IG LTC3728IG#TR LTC3728IG 28-Lead Plastic SSOP 40C to 85C
LTC3728EUH LTC3728EUH#TR 3728 32-Lead (5mm 5mm) Plastic QFN 40C to 85C
LTC3728IUH LTC3728IUH#TR 3728 32-Lead (5mm 5mm) Plastic QFN 40C to 85C
Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container.
For more information on lead free part marking, go to: