LTC4258 datasheet(8/28 Pages) LINER

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LTC4258

4258p

PI FU CTIO S

AGND (Pin 21): Analog Ground. AGND should be con-

nected to the return from the – 48V supply. AGND and

DGND should be tied together.

SENSE4 (Pin 22): Port 4 Current Sense Input. SENSE4

monitors the external MOSFET current via a 0.5

Ω sense

resistor between SENSE4 and VEE. Whenever the voltage

across the sense resistor exceeds the overcurrent detec-

tion threshold VCUT, the current limit fault timer counts up.

If the voltage across the sense resistor reaches the current

limit threshold VLIM (typically 25mV/50mA higher), the

GATE4 pin voltage is lowered to maintain constant current

in the external MOSFET. See Applications Information for

further details. If the port is unused, the SENSE4 pin must

be tied to VEE.

GATE4 (Pin 23): Port 4 Gate Drive. GATE4 should be

connected to the gate of the external MOSFET for port 4.

When the MOSFET is turned on, a 50

µA pull-up current

source is connected to the pin. The gate voltage is clamped

to 13V (typ) above VEE. During a current limit condition,

the voltage at GATE4 will be reduced to maintain constant

current through the external MOSFET. If the fault timer

expires, GATE4 is pulled down with 50

µA, turning the

MOSFET off and recording a tICUT or tSTART event. If the

port is unused, float the GATE4 pin or tie it to VEE.

OUT4 (Pin 24): Port 4 Output Voltage Monitor. OUT4

should be connected to the output port through a 10k

series resistor. A current limit foldback circuit limits the

power dissipation in the external MOSFET by reducing the

current limit threshold when the port voltage is within 18V

of AGND. The port 4 Power Good bit is set when the voltage

from OUT4 to VEE drops below 2V (typ). A 2.5MΩ resistor

is connected internally from OUT4 to AGND. If the port is

unused, the OUT4 pin can be tied to AGND or allowed to

float.

SENSE3 (Pin 25): Port 3 Current Sense Input. See SENSE4.

GATE3 (Pin 26): Port 3 Gate Drive. See GATE4.

OUT3 (Pin 27): Port 3 Output Voltage Monitor. See OUT4.

VEE (Pin 28): – 48V Supply Input. Connect to a – 48V to

– 57V supply, relative to AGND.

SENSE2 (Pin 29): Port 2 Current Sense Input. See SENSE4.

GATE2 (Pin 30): Port 2 Gate Drive. See GATE4.

OUT2 (Pin 31): Port 2 Output Voltage Monitor. See OUT4.

SENSE1 (Pin 32): Port 1 Current Sense Input. See SENSE4.

GATE1 (Pin 33): Port 1 Gate Drive. See GATE 4.

OUT1 (Pin 34): Port 1 Output Voltage Monitor. See OUT4.

AUTO (Pin 35): Auto Mode Input. Auto mode is intended

to allow the LTC4258 to detect and power up a PD even if

there is no host controller present on the I2C bus. The

voltage of the AUTO pin determines the state of the

internal registers when the LTC4258 is reset or comes out

of VDD UVLO (see the Register map in Table 1). The states

of these register bits can subsequently be changed via the

I2C interface if desired. The real-time state of the AUTO pin

can be read at bit 0 in the Pin Status register (11h). Pull

AUTO high or low with

≤10k or tie to VDD or DGND.

NC (Pin 36): No Internal Connection.

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