MAX892LCSLASHD datasheet(6/8 Pages) MAXIM

6 / 8 page

Current-Limited, High-Side

P-Channel Switches with Thermal Shutdown

_______________________________________________________________________________________

______________________________________________________________Pin Description

Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature

exceeds +135°C.

FAULT

Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1µF capacitor to ground.

OUT

7, 8

Set Current-Limit Input. A resistor from SET to ground sets the current limit for the switch. See

Setting the

Current Limit section.

SET

Ground

GND

Active-Low Switch On Input. A logic low turns the switch on.

Input. P-channel MOSFET source. Bypass IN with a 1µF capacitor to ground.

1, 2

FUNCTION

NAME

_______________Detailed Description

The MAX891L/MAX892L P-channel MOSFET power

switches limit output current to a user-programmed

level. When the output current is increased beyond

the set current level, the current is also increased

through the replica switch (IOUT/965) and through

RSET (Figure 1). The current-limit error amplifier com-

pares the voltage across RSET to the internal 1.24V ref-

erence and regulates the current back to the lesser of

the programmed current limit (ILIMIT) or the maximum

current limit (IMAX).

These switches are not bidirectional; therefore, the

input voltage must be higher than the output voltage.

Setting the Current Limit

The MAX891L/MAX892L feature internal current-limit-

ing circuitry with maximum programmable values

(IMAX) of 500mA and 250mA, respectively. For best

performance, set the current limit (ILIMIT) between

0.2IMAX ≤ ILIMIT ≤ IMAX. This current limit remains in

effect throughout the input supply-voltage range.

Program the current limit with a resistor (RSET) from

SET to ground (Figure 2) as follows:

ISET = ILIMIT / IRATIO

RSET = 1.240 / ISET

where ILIMIT is the desired current limit, and IRATIO is

the IOUT to ISET current ratio (965).

Short-Circuit Protection

The MAX891L/MAX892L are short-circuit-protected

switches. In the event of an output short circuit or cur-

rent-overload condition, the current through the switch is

limited by the internal current-limiting error amplifier to

1.5 x ILIMIT. When the fault condition is removed, the

replica error amplifier sets the current limit back to

ILIMIT.

For a high

∆VDS/∆t during an output short-circuit condi-

tion, the switch turns off and disconnects the input sup-

ply from the output. The current-limiting amplifier then

slowly turns the switch on with the output current limited

to 1.5 x ILIMIT. When the fault condition is removed, the

current limit is set back to ILIMIT. Refer to the Current-

Limit Response graphs in the

Typical Operating

Characteristics.

MAX891L

MAX892L

RSET

SET

OUT

GND

1.24V

FAULT

CURRENT-LIMIT

AMPLIFIER

REPLICA

AMPLIFIER

HOT

CONTROL

CIRCUITRY

Figure 1. Functional Diagram

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