LT3640_15 Datasheet, PDF (1/24 Pages) Linear Technology – Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer

LT3640
Dual Monolithic Buck
Regulator with Power-On
Reset and Watchdog Timer
Features
Description
n _{High Voltage Buck Regulator:}
4V to 35V 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
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 _{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 35V; a 36.5V 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 35V
V_OUT1
100k
µP
0.22µF
10µF
EN/UVLO V_IN SW
SYNC
WDE
PGOOD
BST SW1
DA
FB1
100k
RST1
LT3640
V_IN2
RST2
EN2
WDO
WDI
SW2
1.5nF
CWDT
CPOR
FB2
RT GND SS2 SS1
1.5nF
32.4k
1nF
1nF
3.3µH
80.6k
49.9k
1µH
100k
49.9k
3640 TA01a
V_OUT1
3.3V/0.8A
22µF
V_OUT2
1.8V/0.8A
22µF
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
3640f