MAX891L 데이터 시트보기 (PDF) - Maxim Integrated
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MAX891L Datasheet PDF : 8 Pages
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Current-Limited, High-Side
P-Channel Switches 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. See Setting the
Current Limit section.
6
FAULT
Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature
exceeds +135°C.
7, 8
OUT Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1µF capacitor to ground.
_______________Detailed Description
The MAX891L/MAX892L P-channel MOSFET power
switches limit output current to a user-programmed
level. When the output current is increased beyond
the set current level, the current is also increased
through the replica switch (IOUT/965) and through
RSET (Figure 1). The current-limit error amplifier com-
pares the voltage across RSET to the internal 1.24V ref-
erence and regulates the current back to the lesser of
the programmed current limit (ILIMIT) or the maximum
current limit (IMAX).
These switches are not bidirectional; therefore, the
input voltage must be higher than the output voltage.
Setting the Current Limit
The MAX891L/MAX892L feature internal current-limit-
ing circuitry with maximum programmable values
(IMAX) of 500mA and 250mA, respectively. For best
performance, set the current limit (ILIMIT) between
0.2IMAX ≤ 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 / IRATIO
RSET = 1.240 / ISET
where ILIMIT is the desired current limit, and IRATIO is
the IOUT to ISET current ratio (965).
Short-Circuit Protection
The MAX891L/MAX892L are short-circuit-protected
switches. In the event of an output short circuit or cur-
rent-overload condition, 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
MAX891L
MAX892L
OUT
P
REPLICA
AMPLIFIER
ON
P
SET
ON CURRENT-LIMIT
AMPLIFIER
RSET
1.24V
HOT
CONTROL
GND
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 sup-
ply from the output. The current-limiting amplifier then
slowly 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 Current-
Limit Response graphs in the Typical Operating
Characteristics.
6 _______________________________________________________________________________________
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