Power-Good Output

The power-good output, PGOOD (PGOOD), is open-

drain and asserts when the external MOSFET is fully

breaker function (MAX5900N/MAX5901N), PGOOD

(PGOOD) asserts when the external MOSFET is fully

enhanced.

PGOOD (PGOOD) deasserts within 2µs when a circuit-

breaker event occurs or if the die temperature exceeds

for longer than 20ms or ON/OFF is held low for longer

than 20ms.

The MAX5900 PGOOD is active-low and the MAX5901

PGOOD is active-high. Both are open-drain N-channel

withstand up to 100V.

Selecting a Circuit-Breaker Threshold

The MAX5900A/MAX5901A and the MAX5900L/

MAX5901L offer a circuit-breaker function to protect the

external MOSFET and the load from the potentially

damaging effects of excessive current. As load current

generated from drain to source due to the MOSFET’s

breaker threshold, the external MOSFET is turned off

and PGOOD (PGOOD) is deasserted.

To accommodate different MOSFETs and different load

currents, the MAX5900/MAX5901 are available with cir-

cuit-breaker threshold voltages of 200mV, 300mV, and

400mV.

The circuit-breaker function is intended to disconnect

the load if a gross overcurrent or short-circuit condition

occurs. For calculating the circuit-breaker threshold,

condition, and add a 25% overcurrent margin to the

maximum circuit current. For instance, if a MOSFET has

the product of these two numbers, or (0.06

Ω) x (1.75) =

0.105

Ω. Then, if the maximum current is expected to be

2A, using a 25% margin, the current for calculation is

(2A) x (1.25) = 2.5A. The resulting minimum circuit-

breaker threshold is then the product of these two

results, or (0.105

Ω) x (2.5A) = 0.263V. The next highest

minimum available threshold is 0.265V of the

MAX590_ _BEUT, which is an ideal choice given these

parameters. Using this method to choose a circuit-

breaker threshold allows the circuit to operate under

worst-case conditions without causing a circuit-breaker

fault, but the circuit-breaker function will still operate if a

short-circuit or gross overcurrent condition occurs. See

Table 1 for MOSFET suggestions. The MAX5900N/

MAX5901N have no circuit-breaker function. For these

parts choose an external MOSFET that meets the load

requirements.

Determining Inrush Current

Determining a circuit’s inrush current is necessary to

help choose the proper MOSFET. The MAX5900/

MAX5901 regulate the inrush current by means of con-

trolling the load voltage slew rate, but inrush current is

also a function of load capacitance. Determine inrush

current using:

where C is the load capacitance, and SR is the

MAX5900/MAX5901

Load

Voltage

Slew-Rate

Magnitude from the Electrical Characteristics table. For

example, assuming a load capacitance of 100µF, and

using the typical value of 10V/ms for the slew rate, the

inrush current is 1A typical.

If the maximum possible Load Voltage Slew Rate is

used, the maximum inrush current calculates to 1.7A.

Choose a MOSFET with a maximum pulsed current

specification that exceeds the maximum inrush current.

-100V, SOT23/TDFN, Simple Swapper

Hot-Swap Controllers

8

_______________________________________________________________________________________

MAXIMUM

SUGGESTED

EXTERNAL

MOSFET

SUGGESTED

MAXIM PART

0.25

IRFL110

MAX590_ _CEUT

0.5

IRFL4310

MAX590_ _BEUT

1

IRFR3910

MAX590_ _CEUT

2

IRF540NS

MAX590_ _BEUT

3

IRF1310NS

MAX590_ _BEUT

4

IRF1310NS

MAX590_ _CEUT

Suggested External MOSFETs

IS

== ×

C

dV

dt

CR