Document
LT3641
Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer
FEATURES
DESCRIPTION
n High Voltage Buck Regulator: 4V to 42V Operating Range 1.3A Output Current
n Input Transient Protection to 55V n Low Voltage Synchronous Buck Regulator:
2.5V to 5.5V Input Voltage Range 1.1A Output Current n Synchronizable, Adjustable 350kHz to 2.5MHz Switching Frequency n Programmable Power-On Reset Timer n Programmable Window Mode Watchdog Timer n Typical Quiescent Current: 290μA n Short-Circuit Robust n Programmable Soft-Start n Low Shutdown Current: IQ < 1μA n Thermal Shutdown n Available in Thermally Enhanced 28-Lead (4mm × 5mm) QFN and 28-Lead TSSOP Packages
APPLICATIONS
n Industrial Power Supplies n Automotive Electronic Control Units
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
The LT®3641 is a dual channel, current mode monolithic buck switching regulator with a power-on reset and a watchdog timer. Both regulators are synchronized to a single oscillator with an adjustable frequency (350kHz to 2.5MHz). At light loads, both regulators operate in low ripple Burst Mode® to maintain high efficiency and low output ripple.
The high voltage channel is a nonsynchronous buck with an internal 2.4A top switch that operates from an input of 4V to 42V and input transient protection to 55V. The low voltage channel operates from an input of 2.5V to 5.5V. Internal synchronous power switches provide high efficiency without the need of external Schottky diode. Both channels have cycle-by-cycle current limit, providing protection against shorted outputs.
The power-on reset and watchdog timeout periods are both adjustable using external capacitors. The window mode watchdog timer flags when the μP pulses group too close together or too far apart.
The LT3641 is available in a 28-pin 4mm × 5mm QFN package and 28-pin TSSOP package. Both packages have an exposed pad for low thermal resistance.
TYPICAL APPLICATION
2MHz 5V/0.8A and 3.3V/0.5A Step Down Regulators
VIN 7V TO 42V*
VOUT1
100k
μP
0.22μF
10μF
EN/UVLO VIN SW
SYNC WDE PGOOD2
BST SW1
DA FB1
100k
RST1 RST2 WDO WDI
LT3641
VIN2 EN2 SW2
1.5nF
CWDT
FB2
CPOR RT GND SS2 SS1
1.5nF 32.4k
1nF 1nF
4.7μH 301k 100k
2.2μH 226k 49.9k
3641 TA01a
VOUT1 5V/0.8A 22μF
VOUT2 3.3V/0.5A 22μF
* FOR INPUT VOLTAGES ABOVE 42V RESTRICTIONS APPLY
EFFICIENCY (%) EFFICIENCY (%)
HV Channel Efficiency, 2MHz, VOUT1 = 5V
90
VIN = 12V 85
80
75
70 0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 VOUT1 CURRENT (A)
3641 TA01b
LV Channel Efficiency, 2MHz, VOUT2 = 3.3V
95
90 VIN2 = 5V
85
80
75
70 0
0.2 0.4 0.6 0.8 1.0 1.2 VOUT2 CURRENT (A)
3641 TA01c
3641fa
1
LT3641
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN, EN/UVLO Voltage (Note 7) .................................55V WDE Voltage .............................................................30V BST Above SW, SW1 Voltage ....................... –0.3V to 6V SW1 Above SW Voltage............................... –0.3V to 6V VIN2, SYNC, EN2, PGOOD2, WDI, WDO, RST1, RST2, Voltages ....................... –0.3V to 6V SS1, SS2, FB1, FB2, RT, CWDT, CPOR Voltages……….............................. –0.3V to 2.5V
SW2 Voltage ................................ –0.3V to (VIN2 + 0.3V) Operating Junction Temperature Range (Note 2) LT3641E ................................................. –40°C to 125°C LT3641I.................................................. –40°C to 125°C LT3641H................................................. –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature, FE Only (Soldering, 10 sec) .... 300°C
PIN CONFIGURATION
TOP VIEW
FB2 1 PGOOD2 2
28 SS2 27 EN2
EN/UVLO 3
26 GND
SYNC 4
25 SW2
SS1 5 FB1 6
24 VIN2 23 GND
RT 7 29 22 VIN RST2 8 GND 21 BST
RST1 9
20 SW
WDO 10
19 SW1
CWDT 11
18 DA
CPOR 12 WDE 13
17 NC 16 GND
WDI 14
15 GND
FE PACKAGE 28-LEAD PLASTIC TSSOP
θJA = 30°C/W, θJC = 8°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
TOP VIEW
EN/UVLO PGOOD2 FB2 SS2 EN2 GND
28 27 26 25 24 23
SYNC 1
22 SW2
SS1 2
21 VIN2
FB1 3
20 GND
RT 4 RST2 5 RST1 6 WDO 7
29 19 VIN GND 18 BST
17 SW
16 SW1
CWDT 8
15 DA
9 10 11 12 13 14
CPOR WDE WDI GND GND
NC
UFD PACKAGE 28-LEAD (4mm × 5mm) PLASTIC QFN
θJA = 43°C/W, θJC = 3.4°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3641EFE#PBF
LT3641EFE#TRPBF
LT3641FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3641IFE#PBF
LT3641IFE#TRPBF
LT3641FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3641HFE#PBF
LT3641HFE#TRPBF
LT3641FE
28-Lead Plastic TSSOP
–40°C to 150°C
LT3641EUFD#PBF
LT3641EUFD#TRPBF
3641
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3641IUFD#PBF
LT3641IUFD#TRPBF
3641
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
Consult LTC Mar.