Datasheet

LT1910
6
1910fa
PIN FUNCTIONS
BLOCK DIAGRAM
Information). A maximum of 10kΩ can be inserted between
a drain-sense resistor and the SENSE pin. If current sensing
is not required, the SENSE pin is tied to supply.
V
+
(Pin 8): In addition to providing the operating cur-
rent for the LT1910, the V
+
pin also serves as the Kelvin
connection for the current-sense comparator. The V
+
pin
must be connected to the positive side of the drain-sense
resistor for proper current-sensing operation.
–
+
+
–
–
+
3.3V
TIMER
IN
14μA
V
+
2.9V
1.4V
75k
75k
FAULT
–
+
1.4V
250Ω
1910 BD
GATE
SENSE
V
+
65mV
–
+
OSCILLATOR
AND
CHARGE PUMP
–
+
OPERATION
(Refer to the Block Diagram)
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. Conversely,
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 14μA 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
+
pin
must be connected directly to the positive side of the
drain-sense resistor. When the GATE pin is on and the
MOSFET drain current exceeds the level required to gener-
ate 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