LT1910

7

1910fb

For more information www.linear.com/LT1910

operaTion

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 14µA 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).

3.4V

1910 F01

0V

GATE

TIMER

FAULT

IN

OVERCURRENT

NORMAL

NORMAL

OFF

0V

0V

0V

5V

3.5V

2.9V

12V

Figure 1. Timing Diagram

applicaTions inFormaTion

Input/Supply Sequencing

There are no input/supply sequencing requirements for

the LT1910. The IN pin may be taken up to 15V with the

supply at 0V. When the supply is turned on with the IN pin

set HIGH, the MOSFET turn-on will be inhibited until the

timing capacitor charges up to 2.9V (i.e., for one restart

cycle).

Isolating the Inputs

Operation in harsh environments may require isolation to

prevent ground transients from damaging control logic.

TheLT1910easilyinterfacestolowcostoptoisolators.The

network shown in Figure 2 ensures that the input will be

pulled above 2V, but not exceed the absolute maximum

rating for supply voltages of 12V to 48V over the entire

temperature range. The optoisolator must have less than

20µA of dark current (leakage) at hot in order to maintain

the off state (see Figure 2).

Drain-Sense Configuration

The LT1910 uses supply referenced current sensing. One

input of the current-sense comparator is connected to a

drain-sense pin, while the second input is offset 65mV

below the supply inside the device. For this reason, Pin 8

of the LT1910 must be treated not only as a supply pin,

but also as the reference input for the current-sense

comparator.

Figure 3 shows the proper drain-sense configuration for

the LT1910. Note that the SENSE pin goes to the drain

IN

51k

100k

2k

LOGIC

INPUT

12V TO 48V

LT1910

GND

POWER GROUND

LOGIC GROUND

4

FAULT

IN

TIMER

SENSE

GATE

3

4

2

8

6

5

LT1910

R1

5.1k

24V

5V

FAULT OUTPUT

INPUT

0V

GND

Q1

IRFZ34

24V

2A

SOLENOID

1910 F03

C1

100µF

50V

1µF

1

0.02

(PTC)

+

Figure 2. Isolating the Input

Figure 3. Drain-Sense Configuration