LT3689-5_15 Datasheet, PDF (1/34 Pages) Linear Technology – 700mA Step-Down Regulator with Power-On Reset and Watchdog Timer

LT3689/LT3689-5
700mA Step-Down
Regulator with Power-On Reset
and Watchdog Timer
FEATURES
DESCRIPTION
n _{Wide Input Range:}
Operation from 3.6V to 36V
Overvoltage Lockout Protects Circuits through
60V Transients
n _{85µA IQ at 12VIN to 3.3VOUT}
n _{Low Ripple Burst Mode}^® _{Operation Allows Output}
Ripple <15mV_P-P
n _{Programmable, Defeatable Watchdog Timer with}
Window or Timeout Control
n _{Programmable Power-On Reset Timer (POR)}
n _{Synchronizable, Adjustable 350kHz to 2.2MHz}
Switching Frequency
n _{700mA Output Switching Regulator with Internal}
Power Switch
n _{Fixed 5V or Adjustable Output Voltage}
n _{800mV Feedback Voltage}
n _{Programmable Input Undervoltage Lockout with}
Hysteresis
n _{16-Pin 3mm × 3mm QFN and 16-Pin MSOP Packages}
APPLICATIONS
n _{Automotive Electronic Control Units}
n _{Industrial Power Supplies}
The LT^®3689 is an adjustable frequency (350kHz to 2.2MHz)
monolithic step-down switching regulator with a power-on
reset and watchdog timer. The regulator operates from
inputs up to 36V and withstands transients up to 60V. Low
ripple Burst Mode^® operation maintains high efficiency at
low output current while keeping output ripple below 15mV
in a typical application, with input quiescent current of just
85µA. Shutdown circuitry reduces input supply current to
less than 1µA while EN/UVLO is pulled low. Using a resis-
tor divider on the EN/UVLO pin provides a programmable
undervoltage lockout. Current limit, frequency foldback
and thermal shutdown provide fault protection.
The reset and watchdog timeout periods are indepen-
dently adjustable using external capacitors. Tight accuracy
specifications and glitch immunity ensure reliable reset
operation of a system without false triggering. The open
collector RST will pull down if output voltage drops 10%
below the programmed value. The watchdog timer is
pin-selectable for window or timeout modes. In timeout
mode, WDO pulls low if too long of a period passes before
a watchdog transition is detected. In window mode, the
LT3689 monitors for WDI falling edges grouped too close
together or too far apart.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V Regulator with Power-On Reset Timer and Watchdog Timer
V_IN
4.5V TO 36V
TRANSIENT TO 60V
2.2µF
µP
I/O
I/O
RESET
C_WDT
10nF
t_WDU = 182ms
t_WDL = 5.9ms
C_POR
68nF
t_RST = 157ms
V_IN EN/UVLO OUT
BST
WDI
SW
WDO ^LT3689
RST
C_WDT
C_POR
GND
DA
FB
RT
SYNC
f_SW = 700kHz
0.1µF
12µH
10pF
3.3V
700mA
316k
22µF
20.5k 100k
3689 TA01
For more information www.linear.com/LT3689
90
V_IN = 12V
80 ^VOUT ^{= 3.3V}
f = 700kHz
70 L = 12µH
60 ^{TA = 25°C}
Efficiency
50
40
30
20
10
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
1000
100
10
1
1
3689 TA01b
3689fe
1