LT3688_15 Datasheet, PDF (1/28 Pages) Linear Technology – Dual 800mA Step-Down Switching Regulator with Power-On Reset and Watchdog Timer

LT3688
Dual 800mA Step-Down
Switching Regulator with
Power-On Reset and
Watchdog Timer
FEATURES
DESCRIPTION
n _{Wide Input Range:}
Operation from 3.8V to 36V
n _{Low Ripple (<25mVP-P) Burst Mode Operation:}
I_Q = 115μA at 12V_IN to 3.3V and 5V
n _{Programmable, Defeatable Window Watchdog Timer}
n _{Two Independently Programmable Power-On-Reset}
Timers
n _{Synchronizable, Adjustable 350kHz-2.2MHz}
Switching Frequency
n _{Two 800mA Output Switching Regulators with Internal}
Power Switches
n _{Programmable Input Undervoltage Lockout with}
Hysteresis
n _{Thermally Enhanced 24-Pin TSSOP and 4mm × 4mm}
QFN Packages
APPLICATIONS
n _{Automotive Electronic Control Units}
n _{Industrial Power Supplies}
n _{High-Reliability μProcessor Systems}
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
The LT^®3688 is an adjustable frequency (350kHz to
2.2MHz) dual monolithic step-down switching regulator
with two power-on reset timers and a watchdog timer.
The regulator operates off inputs up to 36V. Low ripple
Burst Mode^® operation maintains high efficiency at low
output current while keeping output ripple below 25mV in
a typical application, with input quiescent current of just
115μA. Shutdown circuitry reduces input supply current
to less than 1μA while EN/UVLO is pulled low.
The reset and watchdog timeout periods are both adjust-
able using external capacitors. Tight accuracy specifica-
tions and glitch immunity ensure reliable reset operation
without false triggering. The open collector RST pins will
pull down if the monitored output voltage drops 10%
below the programmed value. The LT3688 watchdog timer
monitors for watchdog falling edges grouped too close
together or too far apart.
The LT3688 is available in 24-Pin TSSOP and 4mm ×
4mm QFN packages, each with an exposed pad for low
thermal resistance.
TYPICAL APPLICATION
5V and 3.3V Regulator with Power-On Reset and Watchdog Timers
V_OUT1
5V
800mA
V_IN
6V TO 36V
18μH
523k
22pF
22μF
100k ^1nF
4.7μF
EN/UVLO V_IN
BST1
0.22μF
SW1
LT3688
DA1
FB1
BIAS
BST2
SW2
DA2
FB2
RUN/SS1
RUN/SS2
μP
I/O
I/O
RESET
WDI
WDO
RST1
RST2
C_WDT
C_POR1
C_POR2
RT
GND ^SYNC
0.22μF 12μH
1nF
316k
22pF
V_OUT2
3.3V
800mA
100k
22μF
4.7nF
110k
f_SW = 500kHz
1nF
4.7nF
3688 TA01a
Efficiency
90 _{VIN = 12V}
V_OUT = 3.3V
80 L = 4.7μH
f = 800kHz
70
10000.0
1000.0
100.0
60
10.0
50
1.0
40
0.1
30
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
0.01
1
3688 TA01b
3688f
1