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LT3581IMSE-TRPBF

3.3A Boost/Inverting DC/DC Converter with Fault Protection

Linear Technology 

LT3581

OPERATION

Refer to the State Diagram (Figure 2) for the following

description of the LT3581’s operation during a fault event.

When a fault is detected, in addition to the FAULT pin being

pulled low internally, the LT3581 also disables its CLKOUT

pin, turns off its power switches, and the GATE pin becomes

high impedance. The external PMOS, M1, turns off when

the gate of M1 is pulled up to its source by the external

RGATE resistor (see Block Diagram). With the external

PMOS turned off, the power path from VIN to VOUT is cut

off, protecting power components downstream.

At the same time, a timeout sequence commences where

the SS pin is charged up to 1.8V (the SS pin will continue

charging up to 2.1V and be held there in the case of a

FAULT1 event that has still not ended), and then discharged

to 50mV. This timeout period relieves the part, the PMOS,

and other downstream power components from electrical

and thermal stress for a minimum amount of time as set

by the voltage ramp rate on the SS pin.

In the absence of faults, the FAULT pin is pulled high by the

external RFAULT resistor (typically 100k). Figure 4 shows

the events that accompany the detection of an output

short on the LT3581.

VOUT

10V/DIV

VFAULT

5V/DIV

VCLKOUT

2V/DIV

IL

2A/DIV

5µs/DIV

3581 F04

Figure 4. Output Short Circuit Protection of the LT3581

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For more information www.linear.com/LT3581

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