IMP2525
Detailed Descriptions
The IMP2525 is a high-side N-channel MOSFET switch that inter-
faces with a USB controller by means of a Switch-Enable input
and a Fault-Flag output. The Enable input turns ON the power
MOSFET with either a logic “1” for the IMP2525-1 or logic “0” for
the IMP2525-2. Any one of three fault conditions will activate the
open-drain Fault-Flag Output to alert the controller that the
power MOSFET has been turned OFF.
Thermal Shutdown
Thermal shutdown is active when the output switch is enabled
(turned ON). Thermal shutdown shuts off the output MOSFET
and sets the Fault Flag if the on-chip temperature sensor exceeds
135°C. The switch is held OFF until the die temperature drops to
125°C or below. This 10°C of hysteresis will result in ON-OFF
short-circuit cycling if the short-circuit condition is not removed
or the bus-controller does turn off the switch with the Enable
input. Over temperature detection is active only if the chip is
enabled.
Input and Output
The IN (input) pin is the power supply connection to the logic cir-
cuitry and the “High-Side” of the switch (the Drain of the power
MOSFET). The OUT (output) pin is the “Low-Side” of the switch
(the Source of the power MOSFET). In a typical circuit, current
flows through the switch from IN to OUT toward the load.
The switch is referred to as a “High-Side” switch since it drives
the positive (or high) side of the load. The output MOSFET source
can be forced to a higher voltage than the drain (V
OUT
> V
IN
) when
the output is OFF with little leakage current. If, however, V
IN
drops below 2.3V, reverse current may flow out the IN pin regard-
less of the enable state.
When the power switch is ON, current can flow in either
direction.
Undervoltage Lockout
The Undervoltage lockout (UVLO) prevents the output
MOSFET from being put into the ON state until the positive sup-
ply voltage, V
IN
, exceeds 2.5V. When the output switch is in the
ON state and the positive supply voltage drops below 2.3V, the
UVLO circuitry will assert the Fault Flag, FLG, and shut OFF the
output MOSFET. The FLG output will only assert an active LOW
state when the MOSFET switch is in the ON state. Undervoltage
detection is active only if the chip is enabled.
Current Limiting
Current limiting is achieved by sensing the voltage drop from
Drain-to-Source of the power MOSFET. When the internal thresh-
old is exceeded the power MOSFET is turned OFF.
Fault Flag - FLG Pin
The Fault Flag pin, FLG, connects to an N-channel, open-drain
MOSFET and goes LOW (“0”) for an occurrence of one or more of
three conditions: undervoltage, current limit, or thermal shut-
down. The FLG output MOSFET is capable of sinking a 10mA
load to typically 100mV above ground.
Table 1
gives the states of
the FLG and OUT pins when a fault condition is detected.
Table 1. Fault Flag Conditions - Switch Enabled
Condition
Thermal Shutdown
Undervoltage Lockout (UVLO)
Current Limiting
Cause
T
J
> 135°C
V
IN
< 2.3V
I
O
> 0.5A (step load)
I
O
> 0.63A (ramped load)
FLG pin “0” Until
T
J
≤
125°C
V
IN
> 2.5V
Enable off or
Thermal Shutdown
Switch State (FLG = “0”)
Turns OFF
Turns OFF
Stays ON
4
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