LT1910 Linear Technology, LT1910 Datasheet - Page 6

• Manufacturer Part Number: LT1910
• Description: Protected High Side MOSFET Driver
• Manufacturer: Linear Technology

BLOCK DIAGRA
LT1910
OPERATIO
The LT1910 GATE pin has two states, OFF and ON. In the
OFF state it is held LOW, while in the ON state it is pumped
to 12V above the supply by a self-contained 750kHz
charge pump. The OFF state is activated when either the IN
pin is below 0.8V or the TIMER pin is below 2.9V. Con-
versely, for the ON state to be activated, the IN pin must be
above 2V and the TIMER pin must be above 2.9V.
The IN pin has approximately 200mV of hysteresis. If it is
left open, the IN pin is held LOW by a 75k resistor. Under
normal conditions, the TIMER pin is held a diode drop
above 2.9V by a 14 A pull-up current source. Thus the
TIMER pin automatically reverts the GATE pin to the ON
state if the IN pin is above 2V.
The SENSE pin normally connects to the drain of the power
MOSFET, which returns through a low value drain sense
resistor to supply. In order for the sense comparator to
accurately sense the MOSFET drain current, the V
must be connected directly to the positive side of the drain
sense resistor. When the GATE pin is ON and the MOSFET
6
TIMER
IN
V
+
75k
U
14 A
3.3V
2.9V
1.4V
75k
(Refer to the Block Diagram)
W
–
+
+
–
+
–
FAULT
+
+
–
pin
1.4V
drain current exceeds the level required to generate a
65mV drop across the drain sense resistor, the sense
comparator activates a pull-down NPN which rapidly pulls
the TIMER pin below 2.9V. This in turn causes the timer
comparator to override the IN pin and set the GATE pin to
the OFF state, thus protecting the power MOSFET. When
the TIMER pin is pulled below 3.3V, the fault comparator
also activates the open-collector NPN to pull the FAULT
pin LOW, indicating an overcurrent condition.
When the MOSFET gate voltage is discharged to less than
1.4V, the TIMER pin is released. The 14 A current source
then slowly charges the timing capacitor back to 2.9V
where the charge pump again starts to drive the GATE pin
HIGH. If a fault condition still exists, the sense comparator
threshold will again be exceeded and the timer cycle will
repeat until the fault is removed. The FAULT pin becomes
inactive HIGH if the TIMER pin charges up successfully
above 3.4V (see Figure 1).
+
–
V
+
–
+
SENSE
65mV
CHARGE PUMP
OSCILLATOR
AND
250
1910 BD
GATE
sn1910 1910fs