LT3640 Datasheet, PDF (1/24 Pages) Linear Technology – Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer

Electrical Specifications Subject to Change
LT3640
Dual Monolithic Buck
Regulator with Power-On
Reset and Watchdog Timer
FEATURES
DESCRIPTION
n _{High Voltage Buck Regulator:}
4V to 36V Operating Range
1.3A Output Current
n _{OVLO Protects Input to 55V}
n _{Low Voltage Synchronous Buck Regulator:}
2.5V to 5.5V Input Voltage Range
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 _{Quiescent Current: 275μA}
n _{Short-Circuit Robust}
n _{Programmable Soft-Start}
n _{Low Shutdown Current: IQ < 1μA}
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^®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.
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.
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 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.
TYPICAL APPLICATION
2MHz 3.3V/0.8A and 1.8V/0.8A Step Down Regulators
V_IN
5V TO 34V
V_OUT1
100k
μP
0.22μF
10μF
EN/UVLO V_IN SW
SYNC
PGOOD
WDE
BST SW1
DA
FB1
100k
RST1
LT3640
V_IN2
RST2
WDO
EN2
WDI
SW2
1.5nF
CWDT
FB2
CPOR RT GND SS2 SS1
1.5nF
32.4k
1nF
1nF
3.3μH
80.6k
49.9k
10μF
1μH
100k
49.9k
3640 TA01a
V_OUT1
3.3V/0.8A
22μF
V_OUT2
1.8V/0.8A
47μF
HV Channel Efficiency,
2MHz, V_OUT1 = 3.3V
90
85
V_IN = 12V
80
75
70
0
0.2 0.4 0.6 0.8 1.0 1.2
V_OUT1 CURRENT (A)
3640 TA01b
LV Channel Efficiency,
2MHz, V_OUT2 = 1.8V
90
V_IN2 = 3.3V
85
80
75
70
0
0.2 0.4 0.6
V_OUT2 CURRENT (A)
0.8
1
3640 TA01c
3640p
1