LTM4656 datasheet(7/28 Pages) AD

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LTM4656/LTM4656-1

Rev. 0

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all COMP pins together for parallel operation. The device is

internal compensated. The LTM4656-1 offers an External

Compensation option.

SENSE1 (A7–A8, B7–B8, C7–C8): These pins are the

output side of the input protection power MOSFET, and

the input to the onboard 4mΩ current sense resistor that

sets maximum input current limit to trip off and retry

in a output short. Measuring the voltage drop between

SENSE1 and BVIN, and dividing by the 4mΩ resistance

gives the input current for a given operating condition in

the boost converter.

RUN (H7): RUN Pin Monitor. The threshold level of 1.28V

will turn on the boost converter. An internal 75k resistor is

connected from this pin to BVIN, and a 5.1V Zener diode to

GNDisinternaltothemoduleforlimitingthevoltageonthe

RUN pin to 5V. The RUN pin is allowed to turn on from an

open-collector control coming from the in-line protection

control when the voltage at the BVIN pin is within 0.5V of

VIN and 3V above GND, indicating the protection MOSFET

is fully on. The state of the pin stays on until the BVIN pin

voltage drops below 2V. See Block Diagram.

INTVCC (G9): Output of Internal 5.4V LDO. Power supply

for internal control circuits and gate drivers. There is an

internal 4.7µF low ESR ceramic capacitor from this pin to

ground for decoupling.

VBIAS (F9): Main Control Supply Pin. It is normally tied

to the input supply BVIN or to the output of the boost

converter. A bypass capacitor should be tied between this

pin and the GND pin. The operating voltage range on this

pin is 4.5V to 36V.

PGOOD (F8): Power Good Indicator. Open-drain logic

output that is pulled to ground when the output voltage is

more than ±10% away from the regulated output voltage.

To avoid false trips, the output voltage must be outside of

the range for 25µs before this output is activated.

TMR (G4): Fault Timer Input. An internal 0.01µF capacitor

to ground sets the times for early fault warning, fault turn-

off, and cooldown periods. The current charging up this

pin during fault conditions depends on the voltage differ-

ence between the VIN and BVIN pins. When TMR reaches

1.275V, the FLT pin pulls low to indicate the detection of a

faultcondition.Iftheconditionpersists,thepasstransistor

turnsoffwhenTMRreachesthethresholdof1.375V.A2µA

current source then continues to pull the TMR up. When

TMR reaches 4.3V, the 2µA current reverses direction and

starts to pull the TMR pin low. When TMR reaches the retry

threshold of 0.5V, the GATE pin pulls high turning back

on the pass transistor. See Typical Applications section.

NC (E3): Float Pin.

SHDN(F1):TheLTM4656canbeshutdowntoalowcurrent

mode when the voltage at the SHDN pin is pulled below the

shutdown threshold of 0.4V. The quiescent current drops

downto40µAwithinternalcircuitryturnedoff.Thispinwill

shut down the in-line protection and the boost converter.

The SHDN pin can be pulled up to VIN MAX or below GND

by up to VIN MAX without damage. The SHDN pin is pulled

up to VIN with an internal 100k resistor for active on. An

VIN rated open collector can be used to controlled this pin

for enabling the in-line protection and the boost converter,

or a Zener diode can be placed from this pin to ground to

interface to lower voltage rated pull downs.

UV (H2): Undervoltage Comparator Input. When UV falls

below its threshold of 1.275V, the GATE pin is pulled down

with a 1mA current. When UV rises above 1.275V plus

the hysteresis, the pull-down current disappears and the

GATE pin is pulled up by the internal charge pump. This is

used to set up an undervoltage lockout to limit the input

current during startup. There is an internal 100k resistor

from this pin to VIN to set up with an external resistor an

under voltage trip point. If unused, connect to VCC. See

Typical Applications section.

FLT (H3): Open Collector Fault Output. This pin pulls low

after the voltage at the TMR pin has reached the fault

threshold of 1.275V. It indicates the pass transistor is

about to turn off because the device is in an overcurrent

condition (current fault). The internal NPN is capable of

sinking up to 100µA of current while maintaining a low

level of 0.8V max.

TEMP+ (H4): Onboard temperature diode for monitoring

each channel with differential connections for noise im-

munity. See Block Diagram.

TEMP– (H5): Onboard temperature diode for monitoring

each channel with differential connections for noise im-

munity. See Block Diagram.

PIN FUNCTIONS

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