Datasheet

LT1683
12
1683fd
OPERATION
There is also an on-chip thermal shutdown circuit that will
turn off the outputs in the event the chip temperature rises
to dangerous levels. Thermal shutdown has hysteresis that
will cause a low frequency (<1kHz) oscillation to occur as
the chip heats up and cools down.
The chip has an undervoltage lockout feature that will
force the gate drivers low in the event that V
IN
drops below
2.5V. This ensures predictable behavior during start-up
and shutdown. SHDN can be used in conjuction with an
external resistor divider to completely disable the part if
the input voltage is too low. This can be used to ensure
adequate voltage to reliably run the converter. See the
section in Applications Information.
Table 1 summarizes these features.
Table 1. Safety and Protection Features
FEATURE FUNCTION EFFECT ON GATE DRIVERS SLEW CONTROL EFFECT ON VC, SS
Maximum Current Fault Turn Off FETs at Maximum
Switch Current (V
SENSE
= 0.1)
Immediately Goes Low Overridden None
Short-Circuit Fault Turn Off FETs and Reset V
C
for Short-Circuit (V
SENSE
= 0.2)
Immediately Goes Low Overridden Discharge V
C
, SS
to GND
Overvoltage Fault Turn Off Drivers If FB > V
REG
+ 0.22V
(Output Overvoltage)
Immediately Goes Low Overridden None
GCL Clamp Set Max Gate Voltage to Prevent
FET Gate Breakdown
Limits Max Voltage None None
Gate Drive
Undervoltage Lockout
Disable Gate Drives When V
IN
Is Too Low. Set Via GCL Pin
Immediately Goes Low Overridden None
Thermal Shutdown Turn Off Drivers If Chip
Temperature Is Too Hot
Immediately Goes Low Overridden None
Opposite Gate Lockout Prevents Opposite Driver from
Turning on Until Driver Is Off
(Cross Conduction in Transformer)
Inhibits Turn On of
Opposite Driver
None None
V
IN
Undervoltage Lockout
Disable Part When V
IN
≅ 2.55V
Immediately Goes Low Overridden None
Gate Drive Source and Sink Current Limit Limit Gate Drive Current Limit Drive Current None None
V5 Source/Sink Current Limit Limit Current from V5 None None None
Shutdown Disable Part When SHDN <1.3V