MAX893 Просмотр технического описания (PDF) - Maxim Integrated

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MAX893

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

MAX893L

SET

RSET

GND

INPUT VOLTAGE

+5V

100k

BLANKED

SIGNAL

TO µP

R

100k

C

0.1µF

IN

OUT

VOUT

MAX893L

ON/OFF

GND

FAULT

SET

RSET

Figure 2. Setting the Current Limit

Figure 3. Fault-Blanking Circuit

Thermal Shutdown

The MAX893L features thermal shutdown. The switch

turns off when the junction temperature exceeds

+165°C. Once the device cools by 10°C, the switch

turns back on. If the fault condition is not removed, the

switch will cycle on and off, resulting in a pulsed out-

put.

Fault Indicator

The MAX893L provides a fault output (FAULT). This

open-drain output goes low when in current limit or

when the die temperature exceeds +165°C. A 100kΩ

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

control signal.

Fault Blanking

During start-up in USB applications, the MAX893L

charges the relatively large USB capacitance. This may

activate an unwanted fault signal if the charging current

exceeds the programmed current limit. To “blank out”

this start-up fault signal, add a simple lowpass RC

delay circuit as shown in Figure 3. This circuit provides

a 10ms delay.

Applications Information

Input Capacitor

To limit the input voltage drop during momentary output

short-circuit conditions, connect a capacitor no more

than 5mm from IN to GND. A 1µF ceramic capacitor will

be adequate for most applications; however, higher

capacitor values will 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 negative during

turn-off.

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 to the device as possible

(no more than 5mm).

Under normal operating conditions, the package can

dissipate and channel heat away. Calculate the maxi-

mum power as follows:

P = (ILIMIT)2 · RON

where RON is the on-resistance of the switch.

When the output is short circuited, the voltage drop

across the switch equals the input supply. Hence, the

power dissipated across the switch increases, as does

the die temperature. If the fault condition is not

removed, the thermal-shutdown protection circuitry

turns the switch off until the die temperature falls by

10°C. A ground plane in contact with the device will

help dissipate additional heat.

Chip Information

TRANSISTOR COUNT: 340

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