LTC4413 datasheet(8/32 Pages) AD

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LTC4421

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

CASIN: Digital Input for Cascading. Connect to CASOUT

of another, higher priority LTC4421 when cascading.

Connect to INTVCC or drive to a supply voltage above 1V

if not used.

CASOUT: Digital Output for Cascading. Connect to the

CASIN of another, lower priority LTC4421 when cascad-

ing. Leave open if not used.

CH1: Voltage Power Source Indicator Output. This open-

drain output pulls low when V1 is powering the output

voltage and releases high otherwise. Connect a pull-up

resistor to a supply less than or equal to 36V to provide

the pull-up. Connect to ground or leave open if unused.

CH2: Voltage Power Source Indicator Output. This open-

drain output pulls low when V2 is powering the output

voltage and releases high otherwise. Connect a pull-up

resistor to a supply less than or equal to 36V to provide

the pull-up. Connect to ground or leave open if unused.

CPO: Charge Pump Output. This is the output of the charge

pump, which is used to provide overdrive to the GATE pins.

Connect a ceramic capacitor between CPO and CPOREF

whose value must be at least 10 times the combined

capacitance of the GATE compensation capacitor plus the

gate capacitance of the back-to-back external N-Channel

MOSFETs of one channel. When the (CPO–CPOREF) voltage

is lower than the CPOGOOD threshold voltage VCPO(UVL),

the input supplies are prevented from powering the output.

See the Operation section for details of the initial start-up

delay due to the time required to charge the CPO capacitor.

CPOREF: Charge Pump Reference Output. This is the

reference point for the charge pump, which is used to

provide overdrive to the GATE pins. Connect to the system

output voltage using a short PCB trace. Do not connect

to the OUT1 or OUT2 sense resistor Kelvin connections.

DISABLE1, DISABLE2: Digital Inputs for Input Disconnect

and Current Limit Fault Reset. Voltages below 1V prevent

the corresponding input V1, V2 supply from powering the

output voltage. Driving DISABLE low, then high after a cur-

rent limit fault resets the current limit timer circuitry and

releases the corresponding FAULT pin high. Connecting

DISABLE to the corresponding FAULT pin configures the

device in auto-retry mode, with a cool-down period between

retries that is 1024 times longer than the current limit fault

time. See Applications Information for more details. Tie to

INTVCC or drive to a supply voltage above 1V if not used.

EXTVCC: External High Priority Supply Input. When EXTVCC

exceeds 2.45V, an internal LDO generates a low voltage

supply rail from EXTVCC to power the low voltage inter-

nal circuitry. Most of the LTC4421’s ICC is drawn from

EXTVCC. Connect EXTVCC to a supply voltage ranging from

3.0V to 36V. Connect EXTVCC to the output voltage (OUT1

or OUT2) to make the output voltage provide the internal

bias current to the LTC4421. If unused, connect to ground,

and the LDO will be powered from another supply.

FAULT1, FAULT2: Current Limit Fault Indicators. These

open-drain outputs pull low when an overcurrent fault

occurs on their corresponding inputs and remain low dur-

ing the cool down cycle. Connect pull-up resistors to a

supply voltage less than or equal to 36V to provide the

pull-up. Tie to ground or leave open if unused.

GATE1, GATE2: Gate Drives for External N-Channel

MOSFETs. Connect these pins to the gates of the exter-

nal back-to-back N-Channel MOSFETs. The charge pump

drives these pins with up to 12V of enhancement. Connect

a capacitor between each GATE pin and the sources of the

corresponding MOSFETs to compensate the current limit

regulation loop.

GND: Device Ground.

INTVCC: Internal Low Voltage Supply Decoupling Output.

An internal LDO generates a low voltage rail to power the

low voltage internal circuitry. It is capable of supplying

up to 500µA of external current. Connect a 1µF or larger

capacitor between this pin and ground to provide bypass-

ing. This pin has an undervoltage lockout threshold volt-

age of 2.3V.

OUT1, OUT2: Output Voltage Sense. The LTC4421 pre-

vents input supplies from connecting to the correspond-

ing OUT until OUT is at least 35mV below the connecting

supply. These pins are also used in conjunction with the

SENSE pins to set the current limit values for the input

supplies. Connect OUT directly to the output side of the

sense resistor with Kelvin connection.

OV1, OV2: Overvoltage Comparator Inputs. Rising input

voltages that cross above 0.5V cause an overvoltage

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