MAX893 データシートの表示（PDF） - Maxim Integrated
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MAX893 Datasheet PDF : 8 Pages
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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
Set Current-Limit Input. A resistor from SET to ground sets the current limit for the switch.
5
SET
RSET = 1.34 · 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 +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 (IMAX), the current also increases through
the replica switch (IOUT / 1080) and through RSET
(Figure 1). The current-limit error amplifier compares
the voltage across RSET to the internal 1.24V reference,
and regulates the current to the programmed current
limit (ILIMIT).
This switch is not bidirectional; therefore, the input volt-
age must be higher than the output voltage.
Setting the Current Limit
The MAX893L features internal current-limiting circuitry
with a maximum programmable value (IMAX) of 1.2A.
For best performance, set the current limit (ILIMIT)
between 0.2A ≤ ILIMIT ≤ 1.2A. 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 / 1080
RSET = 1.24V / ISET = 1.34 · 103 / ILIMIT
where ILIMIT is the desired current limit.
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 · ILIMIT.
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 ILIMIT.
IN
FAULT
N
ON
P
OUT
MAX893L
P
REPLICA
AMPLIFIER
ON
P
SET
ON CURRENT-LIMIT
AMPLIFIER
1.24V
RSET
HOT
GND
CONTROL
CIRCUITRY
Figure 1. Functional Diagram
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
1.5 · ILIMIT. When the short-circuit condition is removed,
the current limit is set back to ILIMIT. See Output Short-
Circuit (Fast-Loop Response) and Output Overload
(Slow-Loop Response) in the Typical Operating
Characteristics.
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