allowing the voltage on the load, i.e. the drain of the

MOSFET, to fall no faster than 10V/ms (typ). The inrush

current to the load is thus limited to a level proportional

to the load capacitance, and the constant load voltage

slew rate. After the MOSFET is fully enhanced, and the

load voltage is settled to its final value, the MAX5900A/

MAX5901A and MAX5900L/MAX5901L monitor the volt-

the voltage drop exceeds 75% of the circuit-breaker

threshold the MAX5900A/MAX5901A or MAX5900L/

MAX5901L turn off the MOSFET, disconnecting the

load immediately. Because the circuit-breaker function

is not activated until the MOSFET is fully enhanced, it

takes approximately 10ms for the MAX5900A/

MAX5901A or MAX5900L/MAX5901L to react to an out-

put short circuit at startup. If no circuit-breaker fault

exists, the power-good output is asserted. Then, if any

of four conditions exist, the power-good output

deasserts and the MOSFET is turned off . The four con-

ditions are: the voltage across the MOSFET exceeds

the circuit-breaker threshold; the supply voltage magni-

tude falls below the undervoltage lockout level; the die

temperature exceeds +125°C; or ON/OFF is forced low.

After a circuit-breaker fault, the MAX5900L/MAX5901L

keep the MOSFET off until the power is cycled, or the

part is reset by toggling ON/OFF low for at least 20ms

(typ). After a circuit-breaker fault, the MAX5900A/

MAX5901A automatically restart in 300ms (typ). All ver-

sions automatically restart after a thermal fault, or an

undervoltage shutdown, if the fault condition goes away

for at least 300ms (typ).

ON/OFF offers external control of the MAX5900/

MAX5901, facilitating power-supply sequencing, and

may also be used to change the UVLO level. UVLO

keeps the external MOSFET switched off as long as the

magnitude of the input voltage is less than a desired

level.

A power-good output, PGOOD (MAX5900) or PGOOD

(MAX5901), asserts when the external MOSFET is fully

enhanced and the drain-source voltage is at least 25%

below the circuit-breaker threshold. PGOOD and

A thermal shutdown feature protects the external MOS-

FET by turning it off if the die temperature of the

MAX5900/MAX5901 exceeds +125°C. The MAX5900/

MAX5901 must be in good thermal contact with the

external MOSFET. See the Layout Guidelines section in

the Applications Information.

A circuit-breaker function monitors the voltage across

circuit-breaker function is enabled after the MOSFET is

fully enhanced. Three threshold voltage options are

available—200mV, 300mV, and 400mV. One version is

available with no circuit-breaker function. circuit-break-

er fault management for the MAX5900/MAX5901 is

offered with two different configurations—latched and

automatic retry.

Latched Circuit Breaker

After a circuit-breaker trip event, the latched versions

the external MOSFET, and PGOOD (PGOOD) is

deasserted. A latched-off condition needs to be reset

by toggling ON/OFF low for at least 20ms, or by cycling

Automatic Retry Circuit Breaker

After a circuit-breaker trip event, the automatic retry

turning off the external MOSFET, and PGOOD

(PGOOD) is deasserted. If the start conditions are met

start conditions are: the device is not in UVLO; ON/OFF

is not driven low; and the device is not in thermal shut-

down.

No Circuit Breaker

For the versions without a circuit-breaker MAX5900N

(MAX5901N), PGOOD (PGOOD) is asserted when the

MOSFET is fully enhanced. Once powered up, the

MAX5900N/MAX5901N ignore the MOSFET drain-to-

breaker function is not desired.

Applications Information

ON

/

OFF Control Input

The ON/OFF control input provides three hot-swap

functions: external ON/OFF control; setting of the UVLO

level; and resetting after a circuit-breaker event has

caused the MAX5900L/MAX5901L to turn off the exter-

external MOSFET (see Figure 2 for a circuit example).

To reset the MAX5900L/MAX5901L after a circuit-

ON/OFF can be used to sequence power supplies.

the rise of ON/OFF proportional to the capacitance and

input impedance of ON/OFF, typically 32k

Ω (Figure 3).

-100V, SOT23/TDFN, Simple Swapper

Hot-Swap Controllers

6

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