LTC4367 datasheet(8/24 Pages) AD

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LTC4381

Rev. 0

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PIN FUNCTIONS

SEL: Output Clamp Voltage Select for LTC4381-1 and

LTC4381-2. Connect the SEL pin to GND to set the inter-

nal output clamp voltage to 28.5V. Connect it to VCC or

OUT for a 47V output clamp voltage. The SEL pin can be

pulled up to 80V or below GND by 60V without damage.

Connect SEL to GND for LTC4381-3 and LTC4381-4.

SNS: Current Sense Input. Connect to the input terminal

of the current sense resistor. The current limit amplifier

controls the GATE pin to limit the current sense voltage

to 50mV. This voltage increases to 62mV in a severe fault

when OUT is below 1.5V. A fixed 6µA is added to the TMR

pin current during an overcurrent condition to shorten the

turn-off time. In a severe short condition when the output

voltage is below 1.5V, the extra current increases to 24µA

to reduce the power dissipation in the MOSFET. ∆VSNS

(SNS – OUT) must be limited to less than ±5V. Connect

to OUT if unused.

SRC: Output of MOSFET. This is the source terminal of the

internal MOSFET, connect this pin to the sense resistor.

The SRC pin and output is indirectly clamped through

GATE pin during an overvoltage event. The LTC4381-1/

LTC4381-2 SRC pin is clamped at 28.5V above GND with

SEL = 0 V, or 47V above GND when SEL = VCC. It is also

clamped at 10.5V above VCC if the VCC voltage is low.

The LTC4381-3/LTC4381-4 SRC pin does not have the

28.5V/47V clamp to GND, it is only clamped at 10.5V

above VCC.

TMR: Fault Timer Input. Connect a capacitor between this

pin and ground to set the fault turn-off time and cool

down period. The charging current during fault conditions

varies depending on the power dissipation of the MOSFET.

When TMR reaches 1.215V, the MOSFET turns off and

FLT pulls low. Upon gate off, the part immediately enters

a cool down period with a 2µA current pull up and pull

down on the TMR pin. After the cool down period has

concluded, the LTC4381-2 and LTC4381-4 immediately

restart, while the LTC4381-1and LTC4381-3 remain off

until the ON pin is pulled low momentarily for more than

100µs or power is cycled. A 10V rated X7R capacitor is

recommended for CTMR.

VCC: Positive Supply Voltage Input. The positive supply

input ranges from 4V to 80V. For applications where the

input voltage is expected to exceed 80V, the VCC pin may

be protected by a Zener diode clamp or, in the case of

short duration spikes, by a simple RC filter. Clamping the

VCC pin with a Zener diode can also be used as a means of

adjusting the output clamp voltage to a value less than the

internal 28.5V/47V clamps for the LTC4381-1/LTC4381-2.

For the adjustable versions, LTC4381-3/LTC4381-4,

which have no internal clamp, a Zener diode at the VCC

pin is the only way to limit the voltage at the output. The

VCC pin can also be powered separately from the VIN pin.

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