LTC4355 datasheet(5/20 Pages) LINER

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LTC4355

4355fe

PIN FUNCTIONS

Exposed Pad: Exposed pad may be left open or connected

to GND.

FUSEFLTx: Fuse Fault Outputs. Open-drain output that

pulls to GND when VINx < 3.5V, indicating that the fuse

has blown open. Otherwise, this output is high impedance.

Connect to GND if unused.

GATEx: Gate Drive Outputs. The GATE pins pull high,

enhancing the N-channel MOSFET when the load cur-

rent creates more than 25mV of voltage drop across

the MOSFET. When the load current is small, the

gates are actively driven to maintain 25mV across the

MOSFET. If the reverse current develops more than

–25mV of voltage drop across a MOSFET, a fast pull-down

circuit quickly connects the GATE pin to the IN pin, turning

off the MOSFET. Limit the capacitance between the GATE

and IN pins to less than 0.1μF.

GND: Device Ground.

INx: Input Voltages and GATE Fast Pull-Down Returns. The

IN pins are the anodes of the ideal diodes and connect to the

sources of the N-channel MOSFETs. The voltages sensed

at these pins are used to control the source-drain voltages

across the MOSFETs and are used by the fault detection

circuits that drive the PWRFLT, FUSEFLT, and VDSFLT pins.

The GATE fast pull-down current is returned through the IN

pins. Connect these pins as close to the MOSFET sources

as possible. Connect to OUT if unused.

MONx: Input Supply Monitors. These pins are used to

sense the input supply voltages. Connect these pins to

external resistive dividers between the input supplies and

GND. If VMONx falls below 1.23V, the PWRFLTx pin pulls

to GND. Connect to GND if unused.

NC: No Connection. Not internally connected. These

pins provide extra distance between high and low volt-

age pins.

OUT: Drain Voltage Sense and Positive Supply Input. OUT

is the diode-OR output of IN1 and IN2. It connects to the

common drain connection of the N-channel MOSFETs. The

voltage sensed at this pin is used to control the source-

drain voltages across the MOSFETs and is used by the

fault detection circuits that drive the PWRFLT and VDSFLT

pins. The LTC4355 is powered from the OUT pin.

PWRFLTx: Power Fault Outputs. Open-drain output

that pulls to GND when VMONx falls below 1.23V or

the forward voltage across the MOSFET exceeds

ΔVSD(FLT). When VMONx is above 1.23V and the

forward voltage across the MOSFET is less than

ΔVSD(FLT), PWRFLTx is high impedance. Connect to GND

if unused.

SET:

ΔVSD(FLT) Threshold Conﬁguration Input. Tying SET

to GND, to a 100k resistor connected to GND, or leaving

SET open conﬁgures the

ΔVSD(FLT) forward voltage fault

threshold to 250mV, 500mV, or 1.5V, respectively. When the

voltage across a MOSFET exceeds

ΔVSD(FLT), the VSDFLT

pin and at least one of the PWRFLT pins pull to GND.

VDSFLT: MOSFET Fault Output. Open-drain output that

pulls to GND when the forward voltage across either

MOSFET exceeds

ΔVSD(FLT). PWRFLT1 or PWRFLT2 also

pulls low to indicate which MOSFET’s forward voltage drop

exceeds

ΔVSD(FLT). Otherwise, this pin is high impedance.

Connect to GND if unused.

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