LTC4413 datasheet(9/32 Pages) AD

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LTC4421

Rev. 0

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event. Connect OV1 and OV2 to a resistive divider between

the respective V1, V2 and ground to set the overvoltage

threshold. See Applications Information section for con-

necting unused OV1 and OV2 pins.

QUAL: OV, UV Qualification Timer. Connect a capacitor

CQUAL from this pin to ground to set an OV, UV qualifica-

tion time of 16ms/nF. Alternatively, connect this pin to

INTVCC to set a default time of 3.5µs. Do not leave open.

RETRY: Digital Input for Retry after Current Limit Fault.

When this pin is above 1V, after a current limit fault dis-

connect occurs, the LTC4421 reconnects the input to the

output up to 6 additional times, waiting for a cool down

period between each reconnection. If current limit faults

occur in each of 6 additional reconnections, the LTC4421

keeps the input disconnected until the input’s DISABLE

pin is toggled. See the Applications section for more

details. Connect to ground if unused. Do not leave open.

SENSE1, SENSE2: Current Sense Non-Inverting Inputs.

The current limit regulation circuits control the GATE pins

to limit the sense voltages between SENSE and OUT to

25mV. If the OUT1 voltage drops below 0.45V, the regula-

tion voltage is reduced from 25mV to 12.5mV. Connect

SENSE1, SENSE2 directly to the input sides of the sense

resistors with Kelvin connections.

SHDN: Digital Input Shutdown to Disconnect Output and

Set Low Current Mode. Voltages below 1V turn off all

external MOSFETs, invalidate both channels and cause

the LTC4421 to enter a low current mode. CASOUT is

pulled high to allow a lower priority LTC4421 in a cas-

caded system to provide power to the output. All circuitry

is debiased, except for the shutdown comparator and low

voltage rail generators, and total device current is reduced

to 6µA. When SHDN is driven back above 1V, the external

MOSFETs are held off until the OV and UV comparators

revalidate. Connect to INTVCC if unused.

SOURCE1, SOURCE2: Connections to Common Sources

of External Back-to-Back N-Channel MOSFETs. Leave

open or connect to the sources of the external MOSFETs.

To minimize channel switchover time, a 5µA pull-down

current biases the MOSFETs on the edge of conduction

when their input supply is not connected to the output.

Add resistors from the MOSFET sources to ground to

PIN FUNCTIONS

increase the MOSFET VGS bias voltage and reduce swi-

tchover time.

TMR1, TMR2: Current Limit Fault Timers. Connect a capaci-

tor between each TMR pin and ground to set a 83ms/µF

duration for current limit before an overcurrent fault occurs.

When a fault occurs, the external N-Channel MOSFETs are

turned off and the corresponding FAULT pin is pulled low.

The LTC4421 can be configured to latch-off, auto-retry

indefinitely or auto-retry 6 additional times after an overcur-

rent fault. See the Applications Information for more details.

UVR1, UVR2: Undervoltage Comparator Inputs for Rising

Voltages. Rising input voltages that cross above 0.5V

are considered valid, provided that the OV pin voltage

is below 0.5V. Connect UVR1 and UVR2 to a resistive

divider between the respective V1, V2 and ground to set

the rising undervoltage threshold. Set the UVR threshold

voltage above the corresponding UVF threshold voltage

to ensure proper operation. See Applications Information

section for connecting unused UVR1 and UVR2 pins.

UVF1, UVF2: Undervoltage Comparator Inputs for

Falling Voltages. Falling input voltages that cross below

0.5V cause an undervoltage event. Connect UVF1 and

UVF2 to a resistive divider between the respective V1,

V2 and ground to set the falling undervoltage threshold.

Set the UVR threshold voltage above the corresponding

UVF threshold voltage to ensure proper operation. See

Applications Information section for connecting unused

UVF1 and UVF2 pins.

V1, V2: Input Power Supply Voltages. Typically V1 and V2

are connected to input supply voltages ranging from 3.0V

to 36V, but each supply can operate down to 0V, provided

another supply voltage ≥3.0V powers the LTC4421. In

normal operation, V1 is the higher priority supply and V2

is the lower priority supply.

VALID1, VALID2: Voltage Valid Indicator Outputs. These

open-drain outputs pull low when their corresponding V1,

V2 inputs are within their OV, UV window for the required

qualification time. Connect pull-up resistors to a supply

voltage less than or equal to 36V to provide the pull-up.

Connect to ground or leave open if unused.

Exposed Pad (Pin 37, UHE Package only): Exposed Pad

may be left open or connected to device ground.

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