MAX5900AAEUT 데이터 시트보기 (PDF) - Maxim Integrated

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MAX5900AAEUT

-100V SOT23 Simple Swapper Hot-Swap Controllers

Maxim Integrated 

100V SOT23 Simple Swapper Hot-Swap

Controllers

Power-Good Output

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

drain and asserts when the external MOSFET is fully

enhanced and VDS is less than VPG (75% of the circuit

breaker threshold, VCB). For versions without the circuit

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

+125°C. PGOOD (PGOOD) deasserts if |VEE| < |VUVLO|

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

MOSFETs with their sources connected to VEE, and can

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

flows through the external MOSFET, a voltage, VDS, is

generated from drain to source due to the MOSFET’s

on-resistance RDS(ON). The MAX5900A/MAX5901A and

MAX5900L/MAX5901L monitor VDS when the external

MOSFET is fully enhanced. If VDS exceeds the circuit

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,

use the MOSFET’s RON at the worst possible operating

condition, and add a 25% overcurrent margin to the

maximum circuit current. For instance, if a MOSFET has

an RON of 0.06Ω at TA = +25°C, and a normalized on-

resistance factor of 1.75 at TA = +130°C (from the

MOSFET data sheet), the RON used for calculation is

the product of these two numbers, or (0.06Ω) x (1.75) =

0.105Ω. 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 (0.105Ω) 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:

I = C dV = C × SR

dt

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.

Suggested External MOSFETs

MAXIMUM

ILOAD (A)

SU GG ESTED

EXTER N AL

M O SF ET

0.25

IRFL110

0.5

IRFL4310

1

IRFR3910

2

IRF540NS

3

IRF1310NS

4

IRF1310NS

VIN = -9V to -90V

SU GG ESTED

MAXIM PART

MAX590_ _CEUT

MAX590_ _BEUT

MAX590_ _CEUT

MAX590_ _BEUT

MAX590_ _BEUT

MAX590_ _CEUT

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