MAX890L
1.2A, Current-Limited, High-Side
P-Channel Switch with Thermal Shutdown
6 _______________________________________________________________________________________
Pin Description
Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1μF capacitor to ground.OUT6, 7
Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature
exceeds +135°C.
FAULT
8
Set Current-Limit Input. A resistor from SET to ground sets the current limit for the switch.
R
SET
= 1.38 x 10
3
/I
LIMIT,
where I
LIMIT
is the desired current limit in amperes.
SET5
GroundGND4
PIN
Active-Low Switch On Input. A logic low turns the switch on.
ON
3
Input. P-channel MOSFET source. Bypass IN with a 1μF capacitor to ground.IN1, 2
FUNCTIONNAME
Detailed Description
The MAX890L 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
/1110) and through R
SET
(Figure 1). The current-limit error amplifier compares
the voltage across R
SET
to the internal +1.24V refer-
ence and regulates the current back to the lesser of the
programmed limit (I
LIMIT
) or 1.2A.
This switch is not bidirectional; therefore, the input volt-
age must be higher than the output voltage.
Setting the Current Limit
The MAX890L 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 0.2 I
MAX
≤ I
LIMIT
≤ I
MAX
. 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
/ 1110
R
SET
= 1.24V / I
8
= 1.38 x 10
3
/ I
LIMIT
where I
LIMIT
is the desired current limit.
Short-Circuit Protection
The MAX890L is a short-circuit-protected switch. In the
event of an output short circuit or current-overload con-
dition, the current through the switch is limited by the
internal current-limiting error amplifier to 1.5 x I
LIMIT
.
When the fault condition is removed, the replica error
amplifier sets the current limit back to I
LIMIT
.
For a high dV
DS
/dt 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 x I
LIMIT
. When the fault condition is removed, the
current limit is set back to I
LIMIT
. Refer to the Output
Short-Circuit Fast-Loop Response and Output Overload
Slow-Loop Response in the
Typical Operating
Characteristics
.
