MAX890L Просмотр технического описания (PDF) - Maxim Integrated

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MAX890L

1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown

Maxim Integrated 

1.2A, Current-Limited, High-Side

P-Channel Switch with Thermal Shutdown

Pin Description

PIN NAME

FUNCTION

1, 2

IN

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

3

ON

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

4

GND Ground

5

SET

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

RSET = 1.38 x 103/ILIMIT, where ILIMIT is the desired current limit in amperes.

6, 7

OUT

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

8

FAULT

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

exceeds +135°C.

Detailed Description

The MAX890L P-channel MOSFET power switch limits

output current to a programmed level. When the output

current is increased beyond the programmed current

limit, or 1.2A (IMAX), the current also increases through

the replica switch (IOUT/1110) and through RSET

(Figure 1). The current-limit error amplifier compares

the voltage across RSET to the internal +1.24V refer-

ence and regulates the current back to the lesser of the

programmed limit (ILIMIT) or 1.2A.

This switch is not bidirectional; therefore, the input volt-

age must be higher than the output voltage.

Setting the Current Limit

The MAX890L features internal current-limiting circuitry

with a maximum programmable value (IMAX) of 1.2A.

For best performance, set the current limit (ILIMIT)

between 0.2 IMAX ≤ 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 / 1110

RSET = 1.24V / I8 = 1.38 x 103 / ILIMIT

where ILIMIT is the desired current limit.

Short-Circuit Protection

The MAX890L is a short-circuit-protected switch. In the

event of an output short circuit or current-overload con-

dition, 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.

IN

FAULT

N

ON

P

OUT

MAX890L

P

REPLICA

AMPLIFIER

ON

P

SET

ON CURRENT-LIMIT

AMPLIFIER

RSET

1.24V

HOT

CONTROL

GND

CIRCUITRY

Figure 1. Functional Diagram

For a high dVDS/dt during an output short-circuit condi-

tion, the switch turns off and disconnects the input supply

from the output. The current-limiting amplifier then slow-

ly 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 Output

Short-Circuit Fast-Loop Response and Output Overload

Slow-Loop Response in the Typical Operating

Characteristics.

6 _______________________________________________________________________________________

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