LT4239 datasheet(6/24 Pages) AD

6 / 24 page

LT4239

Rev. 0

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PIN FUNCTIONS

OUT (Pin 1): MOSFET Gate Drive Return. Connect this

pin to the output side of the current sense resistor. The

gate fast pull-down current returns through this pin when

gates are discharged. GATE2 is pulled low quickly when

OUT falls below 3.7V after power good.

OUTK (Pin 2): Negative Current Sense Input. Connect to

the output terminal of the current sense resistor.

SENSE1, SENSE2 (Pins 4, 3): Positive Current Sense

Input. Connect to the input side of the current sense resis-

tor. The current limit circuit controls GATE1 to limit the

voltage between SENSE1 and OUTK to 50mV for 100µs

before fault latched-off during start-up. After GATE2

turns on, the circuit breaker will trip when the voltage

between SENSE2 and OUTK exceeds 10mV longer than

the overcurrent fault timer period. During an overload

condition, GATE2 is regulated to maintain 15mV of voltage

drop across SENSE2 and OUTK for 100µs before fault

latched-off.

GATE2 (Pin 5): Gate Drive for External N-Channel

MOSFETs. An internal 50µA current source starts charging

up the gate of the Bypass MOSFET when ∆VGATE1 is higher

than 10V and VIN – VOUT < 1V. GATE2 is limited to 12V

above OUT by internal clamps. A 10mA current source

keeps the MOSFET off when the part is in undervoltage

condition. When a short-circuit condition is detected,

GATE2 is pulled down to OUT by a 50mA current source.

This current increases to 600mA when a severe output

short is detected.

GATE1 (Pin 6): Gate Drive for External N-Channel MOSFET.

An internal 10µA current source charges up the gate of

the Start-up MOSFET. The inrush current can be limited

by the additional R-C network from GATE1 to GND by

controlling its slew rate. GATE1 is limited to 12V above

OUT by internal clamps. GATE1 turns off when power

good condition, ∆VGATE2 ≥ 10V and VIN – VOUT < 100mV,

are achieved. A 10mA current source keeps the MOSFET

off when the part is in undervoltage condition. When a

short-circuit condition is detected, GATE1 is pulled down

to OUT by a 10mA current source. This current increases

to 130mA when a severe output short is detected.

DRAIN (Pin 7): External MOSFET’s Drain Sense Input.

Connect a 100k resistor between this pin and the drain

of the external N-Channel MOSFET to monitor the differ-

ence between MOSFET’s drain and OUTK voltages. The

voltage sensed at this pin enables the GATE2 start-up

and power good delay after GATE1 is fully enhanced. If

the voltage between the MOSFET’s drain and OUTK rises

above 100mV after power good, a 20ms FET-Bad fault

timer will be activated.

VCC (Pin 8): Positive Supply Input. If supply voltage

spikes might exceed 25V, connect an RC filter at this pin.

This pin has an undervoltage lockout threshold of 3.6V

that will turn off all the MOSFETs.

STMR (Pin 9): Start-Up Timer. Connect a capacitor

between this pin and ground to set a 123ms/µF duration

for start-up. If either the MOSFET gate drive at GATE1

remains below 10V or the voltage between MOSFET’s

drain and OUTK is greater than 100mV at the end of the

start-up timer ramp-up, the start-up cycle is aborted.

GATE1 pulls low turning off the MOSFET and FLT pulls

low to indicate a start-up fault.

UV (Pin 10): Undervoltage Comparator Input. Connect to

an external resistive voltage divider from the input sup-

ply to monitor the supply voltage. This pin has a 25ms

debounce time on the rising edge before GATE1 start-up.

If the voltage at this pin falls below 1.182V, an undervolt-

age fault is detected and all the MOSFETs will be turned

off. Pulling the UV pin below 0.6V resets the fault latch

after a fault due to start-up failure, overcurrent, or FET

short. Connect to VCC if unused.

CBTMR (Pin 11): Overcurrent Fault Timer. Connect a

capacitor between this pin and ground to set a 123ms/

µF duration for circuit breaker timeout, after which an

overcurrent fault is generated and GATE2 is pulled low.

The duration of the cool down time is 185s/µF when

the device is configured for auto-retry, resulting in a

0.06% duty cycle.

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