Electrical Specifications Subject to Change
LT3640
Dual Monolithic Buck
Regulator with Power-On
Reset and Watchdog Timer
FEATURES
DESCRIPTION
The LT®3640 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.
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High Voltage Buck Regulator:
4V to 36V Operating Range
1.3A Output Current
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OVLO Protects Input to 55V
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Low Voltage Synchronous Buck Regulator:
2.5V to 5.5V Input Voltage Range
1A Output Current
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Synchronizable, Adjustable 350kHz to 2.5MHz
The high voltage channel is a nonsynchronous buck with
an internal 2.4A top switch that operates from an input
of 4V to 36V; a 38V OVLO protects the device 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.
Bothchannelshavecycle-by-cyclecurrentlimit,providing
protection against shorted outputs.
Switching Frequency
Programmable Power-On Reset Timer
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Programmable Window Mode Watchdog Timer
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Quiescent Current: 275μA
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Short-Circuit Robust
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Programmable Soft-Start
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Low Shutdown Current: I < 1μA
Q
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Available in Thermally Enhanced 28-Lead
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.
(4mm × 5mm) QFN and 28-Lead TSSOP Packages
APPLICATIONS
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Industrial Power Supplies
Automotive Electronic Control Units
The LT3640 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.
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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.
TYPICAL APPLICATION
2MHz 3.3V/0.8A and 1.8V/0.8A Step Down Regulators
HV Channel Efficiency,
2MHz, VOUT1 = 3.3V
LV Channel Efficiency,
2MHz, VOUT2 = 1.8V
0.22μF
V
IN
5V TO 34V
10μF
3.3μH
80.6k
90
85
80
75
70
90
85
80
75
70
V
OUT1
EN/UVLO
V
SW
BST SW1
IN
3.3V/0.8A
V
IN2
= 3.3V
SYNC
PGOOD
WDE
22μF
DA
FB1
V
IN
= 12V
49.9k
10μF
V
OUT1
100k
100k
μP
LT3640
V
IN2
RST1
RST2
WDO
WDI
EN2
1μH
V
OUT2
SW2
1.8V/0.8A
100k
47μF
CWDT
CPOR
FB2
RT GND SS2 SS1
49.9k
0
0.2
0.4
0.6
0.8
1.0
1.2
0
0.2
0.4
0.6
0.8
1
1nF
1.5nF
1.5nF
32.4k
V
CURRENT (A)
V
OUT2
CURRENT (A)
OUT1
1nF
3640 TA01b
3640 TA01c
3640 TA01a
3640p
1