1A Current-Limited Switch for 2 USB Ports
MAX1922
Pin Description
PACKAGE
TDFN
6
1, 3, 9
5
7
2, 4,
8, 10
—
SO
1
2, 3
4
5
6, 7,
8
—
NAME
GND
IN
EN
OC
OUT
EP
Ground
Input. p-channel MOSFET source—connect all IN pins together and bypass with a 1µF capacitor ground.
Active-Low Switch Enable Input. A logic-low turns on the switch.
Overcurrent-Indicator Output. This open-drain output goes low when the device is in thermal shutdown
or undervoltage lockout, or during a sustained (10ms) current-limit condition.
Switch Output. p-channel MOSFET drain—connect all OUT pins together and bypass with a 0.1µF
capacitor to ground.
TDFN Only. Exposed paddle. Connect to the GND plane for optimum thermal dissipation. This does not
remove the requirement for a proper ground.
FUNCTION
Continuous Short-Circuit Protection
IN
P
OUT
MAX1922
OC
P
The MAX1922 is a short-circuit-protected switch. In the
event of an output short-circuit condition, the current
through the switch is foldback-current-limited to 1A
continuous.
Thermal Shutdown
N
REPLICA
AMPLIFIER
ON
P
The MAX1922 has a thermal shutdown feature. The
switch turns off and the
OC
output goes low immediate-
ly (no overcurrent blanking) when the junction tempera-
ture exceeds +165°C. When the MAX1922 cools 20°C,
the switch turns back on. If the fault short-circuit condi-
tion is not removed, the switch cycles on and off, result-
ing in a pulsed output.
ON
CURRENT-LIMIT
AMPLIFIER
1.24V
OC
Indicator
The MAX1922 provides an overcurrent output (OC). A
100kΩ pullup resistor from
OC
to IN provides a logic
control signal. This open-drain output goes low when
any of the following conditions occur:
•
The input voltage is below the 2.4V undervoltage
lockout (UVLO) threshold.
•
The die temperature exceeds the thermal shutdown
temperature limit of +165°C.
•
The device is in current limit for greater than 10ms.
10ms
TIMER
HOT
EN
CONTROL
CIRCUITRY
GND
Figure 1. Functional Diagram
Detailed Description
The MAX1922 p-channel MOSFET power switch limits
output current to 1.4A min and 2.1A max. When the out-
put current increases beyond the current limit (I
LIMIT
),
the current also increases through the replica switch
(I
OUT
/ 13000). The current-limit error amplifier com-
pares the voltage to the internal 1.24V reference and
regulates the current back to the I
LIMIT
(Figure 1).
These switches are not bidirectional; therefore, the
input voltage must be higher than the output voltage.
6
OC
Blanking
The MAX1922 features 10ms overcurrent blanking.
Blanking allows brief current-limit faults, including
momentary short-circuit faults that occur when hot-
swapping a capacitive load, and ensures that no
OC
is
issued during power-up. When a load transient causes
the device to enter current limit, an internal counter
starts. If the load fault persists beyond the 10ms over-
current blanking timeout, the
OC
output asserts low.
Ensure that the MAX1922 input is adequately bypassed
to prevent input glitches from triggering spurious
OC
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