LTC4366 datasheet(8/22 Pages) AD

8 / 22 page

LTC4249

Rev. 0

For more information www.analog.com

OPERATION

The LTC4249 is a two channel 65V electronic circuit

breaker (ECB) with current monitoring outputs. Circuit

breaker input IN1 has a 6V to 65V voltage input range

and provides internal operating bias for the LTC4249. IN2

input range is 1.5V to 65V when IN1 is biased. Load cir-

cuits typically connect to OUT. The circuit breakers close

when EN is high and open when EN is low. The ready

(RDY) outputs pull low when the ECBs are off and are

released when ECBs are on.

When RDY is released, an accurate scaled replica of the

output load current is sourced from the IMON outputs. A

resistor connected from IMON to GND converts the scaled

current to a voltage. If the IMON voltage exceeds 1.2V,

an overcurrent fault is deemed to exist; the ECB turns off

and RDY pulls low.

Each enable input is compared to an internal 0.8V refer-

ence to enable or disable its respective channel. While

a standard GPIO can be used to drive these inputs, the

precision reference allows an external resistive divider to

be used as an adjustable UVLO (undervoltage lockout)

based on the applied input voltage. If the applied voltage

falls below the EN falling threshold, the circuit breaker

turns off. See the Applications Information for examples.

When initially enabled, the ECB enters a current limited

operating phase, limiting inrush current without the

need for external components. During the current lim-

ited operating phase, OUT is charged with a 1A current

source for 10ms. Maximum allowable OUT capacitance

is 100µF. If OUT fails to charge beyond 1.2V in the first

300µs after enable, the output is deemed shorted and the

circuit breaker turns off. At the successful conclusion of

the current limited operating phase, the ECB enters low

RON operation (75mΩ typical).

At this point, the analog current monitor function begins

to source current to the IMON output. The 5% accurate

current monitor produces 100µA/A of output load current,

useful for closed loop load bias control or monitoring

(see Applications Information for details). Internally, two

comparators with different thresholds sense the voltage

developed on the IMON output. The primary threshold

comparator has a 1.2V threshold. It contains built-in filter-

ing to remove glitches which could cause chatter near the

primary threshold. The filter characteristic is shown in the

Applications Information. The secondary comparator has

a 2.4V threshold with a 2µs response time, to quickly open

the ECB in situations with large overcurrent.

Overcurrent (VIMON > 1.2V) or short-circuit (OUT < 1.2V)

faults latch the circuit breaker off. Toggling EN clears the

latch and turns the circuit breaker on. After an overtem-

perture fault, both channels turn off. The enables must

be toggled in order to turn the respective ECBs back on.

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