1.2A, Current-Limited, High-Side
P-Channel Switch with Thermal Shutdown
MAX893L
Pin Description
PIN
1, 2
3
4
5
6, 7
8
NAME
IN
ON
GND
SET
OUT
FAULT
FUNCTION
Input. P-channel MOSFET source. Bypass IN with a 1µF capacitor to ground.
Active-Low Switch On Input. A logic low turns the switch on.
Ground
Set Current-Limit Input. A resistor from SET to ground sets the current limit for the switch.
R
SET
= 1.34
·
10
3
/ I
LIMIT,
where I
LIMIT
is the desired current limit in amperes.
Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1µF capacitor to ground.
Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature
exceeds +165°C.
Detailed Description
The MAX893L 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 (I
MAX
), the current also increases through
the replica switch (I
OUT
/ 1080) and through R
SET
(Figure 1). The current-limit error amplifier compares
the voltage across R
SET
to the internal 1.24V reference,
and regulates the current to the programmed current
limit (I
LIMIT
).
This switch is not bidirectional; therefore, the input volt-
age must be higher than the output voltage.
IN
P
OUT
MAX893L
FAULT
P
N
REPLICA
AMPLIFIER
ON
P
SET
ON
CURRENT-LIMIT
AMPLIFIER
1.24V
Setting the Current Limit
The MAX893L features internal current-limiting circuitry
with a maximum programmable value (I
MAX
) of 1.2A.
For best performance, set the current limit (I
LIMIT
)
between 0.2A
≤
I
LIMIT
≤
1.2A. This current limit remains
in effect throughout the input supply-voltage range.
Program the current limit with a resistor (R
SET
) from
SET to ground (Figure 2) as follows:
I
SET
= I
LIMIT
/ 1080
R
SET
= 1.24V / I
SET
= 1.34
·
10
3
/ I
LIMIT
where I
LIMIT
is the desired current limit.
ON
CONTROL
CIRCUITRY
R
SET
HOT
GND
Figure 1. Functional Diagram
Short-Circuit Protection
The MAX893L is a short-circuit protected switch. In the
event of an output short circuit or a current overload
condition, the current through the switch is limited by
the internal current-limiting error amplifier to 1.5
·
I
LIMIT
.
The short-circuit current is typically 1.8A for a pro-
grammed current limit of 1.2A. When the short-circuit
condition is removed, the replica error amplifier will set
the current limit back to I
LIMIT
.
For a high
∆V
DS
/∆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
1.5
·
I
LIMIT
. When the short-circuit condition is removed,
the current limit is set back to I
LIMIT
. See Output Short-
Circuit (Fast-Loop Response) and Output Overload
(Slow-Loop Response) in the
Typical Operating
Characteristics.
6
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