MAX894L Просмотр технического описания (PDF) - Maxim Integrated

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MAX894L

2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown

Maxim Integrated 

2A, Current-Limited, High-Side

P-Channel Switch with Thermal Shutdown

IN

FAULT

N

P

OUT

MAX869L

P

REPLICA

AMPLIFIER

ON

P

MAX869L

SET

RSET

GND

SET

ON CURRENT-LIMIT

AMPLIFIER

1.24V

RSET

Figure 2. Setting the Current Limit

HOT

ON

CONTROL

GND

CIRCUITRY

Figure 1. Functional Diagram

Short-Circuit Protection

The MAX869L is a short-circuit-protected switch. In the

event of an output short circuit (VOUT ≤ 1.6V typical),

the current through the switch is limited by the internal

current-limiting error amplifier to 1.4 x ILIMIT. When the

short-circuit condition is removed, the current-limit

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 supply

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

ly turns the switch on with the output current limited to

1.4 x ILIMIT. When the short-circuit condition is

removed, the current limit is set back to ILIMIT. Refer to the

Fast Current-Limit Response and Slow Current-Limit

Response graphs in the Typical Operating Characteristics.

Thermal Shutdown

The MAX869L features thermal shutdown. The switch

turns off when the junction temperature exceeds 135°C.

Once the device cools by 10°C, the switch turns back

on. If the fault condition is not removed, the switch

cycles on and off, resulting in a pulsed output.

Fault Indicator

The MAX869L provides a fault output (FAULT). This

open-drain output goes low when in current limit or

when the die temperature exceeds 135°C. A 100kΩ

pull-up resistor from FAULT to IN provides a logic-

control signal.

__________Applications Information

Input Capacitor

To limit the input voltage drop during momentary output

short-circuit conditions, connect a capacitor from IN to

GND. A 1µF ceramic capacitor is adequate for most

applications; however, higher capacitor values further

reduce the voltage drop at the input.

Output Capacitor

Connect a 0.1µF capacitor from OUT to GND to prevent

inductive parasitics from pulling OUT below GND dur-

ing turn-off. USB applications require COUT to be at

least 120µF. This larger output capacitance slows the

output rise and fall times, as shown in the Typical

Operating Characteristics, but does not adversely

affect the MAX869L’s turn-off response time.

Layout and Thermal-Dissipation

Considerations

To take full advantage of the switch-response time to

output short-circuit conditions, it is very important to

keep all traces as short as possible to reduce the effect

of undesirable parasitic inductance. Place input and

output capacitors as close as possible to the device

(less than 5mm).

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