LT3641
1
3641fa
TYPICAL APPLICATION
DESCRIPTION
Dual Monolithic Buck
Regulator with Power-On
Reset and Watchdog Timer
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 effi ciency 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
effi ciency 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 fl ags 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.
2MHz 5V/0.8A and 3.3V/0.5A Step Down Regulators
FEATURES
APPLICATIONS
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: I
Q
< 1μA
n
Thermal Shutdown
n
Available in Thermally Enhanced 28-Lead
(4mm × 5mm) QFN and 28-Lead TSSOP Packages
n
Industrial Power Supplies
n
Automotive Electronic Control Units
3641 TA01a
SYNC
PGOOD2
WDE
1nF
1nF
1.5nF
1.5nF
* FOR INPUT VOLTAGES ABOVE 42V RESTRICTIONS APPLY
32.4k
V
OUT2
3.3V/0.5A
V
OUT1
5V/0.8A
22μF
10μF
100k
RST2
EN2
WDO
WDI
FB2
CWDT
CPOR RT GND SS2 SS1
RST1
SW2
SW1EN/UVLO V
IN
V
IN
7V TO 42V*
SW
LT3641
BST
V
IN2
FB1
2.2μH
100k
V
OUT1
μP
226k
49.9k
301k
100k
4.7μH
0.22μF
DA
22μF
HV Channel Effi ciency,
2MHz, V
OUT1
= 5V
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.
LV Channel Effi ciency,
2MHz, V
OUT2
= 3.3V
V
OUT1
CURRENT (A)
0
70
EFFICIENCY (%)
80
0.2 0.4 0.80.6 1.0
90
75
85
1.2 1.4
3641 TA01b
V
IN
= 12V
V
OUT2
CURRENT (A)
0
70
EFFICIENCY (%)
80
0.2 0.4 0.8 1.00.6 1.2
95
90
75
85
3641 TA01c
V
IN2
= 5V