LTC2913 datasheet(8/26 Pages) AD

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LT4356-1/LT4356-2

Rev. C

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PIN FUNCTIONS

AOUT (DFN and SO Packages Only): Amplifier Output.

Opencollectoroutputoftheauxiliaryamplifier.Itiscapable

of sinking up to 2mA from 80V. The negative input of the

amplifier is internally connected to a 1.25V reference.

EN: Open-Collector Enable Output. The EN pin goes high

impedance when the voltage at the OUT pin is above (VCC

– 0.7V), indicating the external MOSFET is fully on. The

state of the pin is latched until the OUT pin voltage resets

at below 0.5V and goes back up above 2V. The internal

NPN is capable of sinking up to 3mA of current from 80V

to drive an LED or opto-coupler.

Exposed Pad (DFN Package Only): Exposed pad may be

left open or connected to device ground (GND).

FB: Voltage Regulator Feedback Input. Connect this pin

to the center tap of the output resistive divider connected

between the OUT pin and ground. During an overvoltage

condition, the GATE pin is servoed to maintain a 1.25V

threshold at the FB pin. This pin is clamped internally to

7V. Tie to GND to disable the OV clamp.

FLT: Open-Collector Fault Output. This pin pulls low after the

voltageattheTMRpinhasreachedthefaultthresholdof1.25V.

It indicates the pass transistor is about to turn off because

eitherthesupplyvoltagehasstayedatanelevatedlevelforan

extended period of time (voltage fault) or the device is in an

overcurrentcondition(currentfault).TheinternalNPNiscapa-

bleofsinkingupto3mAofcurrentfrom80VtodriveanLEDor

opto-coupler.

GATE: N-Channel MOSFET Gate Drive Output. The GATE

pin is pulled up by an internal charge pump current source

and clamped to 14V above the OUT pin. Both voltage and

current amplifiers control the GATE pin to regulate the

output voltage and limit the current through the MOSFET.

GND: Device Ground.

IN+ (DFN and SO Packages Only): Positive Input of the

Auxiliary Amplifier. This amplifier can be used as a level

detection comparator with external hysteresis or linear

regulator controlling an external PNP transistor. This pin

is clamped internally to 7V. Connect to ground if unused.

OUT: Output Voltage Sense Input. This pin senses the

voltage at the source of the N-channel MOSFET and sets

the fault timer current. When the OUT pin voltage reaches

0.7V away from VCC, the EN pin goes high impedance.

SHDN: Shutdown Control Input. Pulling the SHDN pin low

shuts the part down to a low current mode. All functions

are turned off for the LT4356-1 while the internal reference

and the auxiliary amplifier stay active for the LT4356-2.

The SHDN input threshold is similar to a TTL input. If the

SHDN voltage goes below 2.1V, the voltage must go below

0.4V for 100μs to properly shut down the part. To turn

the part back on, the SHDN voltage must transition from

below 0.4V to greater than 2.1V with a slew rate faster

than 10V/ms. An internal, 4μA current source is provided

to pull the SHDN pin up. An external pull-up device should

be used if the leakage current to ground might exceed 1μA.

The SHDN pin can be pulled up to 100V or below GND by

60V without damage.

SNS:CurrentSenseInput.Connectthispintotheoutputof

thecurrentsenseresistor.Thecurrentlimitcircuitcontrols

the GATE pin to limit the sense voltage between VCC and

SNS pins to 50mV. At the same time the sense amplifier

also starts a current source to charge up the TMR pin.

This pin can be pulled below GND by up to 60V, though

the voltage difference with the VCC pin must be limited to

less than 30V. Connect to VCC if unused.

TMR: Fault Timer Input. Connect a capacitor between this

pin and ground to set the times for early warning, fault

and cool down periods. The current charging up this pin

during fault conditions depends on the voltage difference

between the VCCandOUTpins.WhenVTMRreaches1.25V,

the FLT pin pulls low to indicate the detection of a fault

condition.Iftheconditionpersists,thepasstransistorturns

off when VTMR reaches the threshold of 1.35V. As soon as

the fault condition disappears, the pull up current stops

and a 2µA current starts to pull the TMR pin down. When

VTMRreachestheretrythresholdof0.5V,theGATEpinpulls

high turning back on the pass transistor. A minimum of

10nF capacitor is needed to compensate the loop. A 10V

rated X7R capacitor is recommended for CTMR.

VCC: Positive Supply Voltage Input. The positive supply

input ranges from 4V to 80V for normal operation. It

can also be pulled below ground potential by up to 60V

during a reverse battery condition, without damaging the

part. The supply current is reduced to 7µA with all the

functional blocks off.

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