IMP2526
Detailed Descriptions
The IMP2526 dual high-side N-channel MOSFET switch inter-
faces with a USB controller by means of a Switch-Enable input
and a Fault-Flag output. The Enable input, with either a logic “1”
for the IMP2526-1 or logic “0” for the IMP2526-2, turns the power
MOSFET ON. 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
circuitry and the “High-Side” of the switch (the Drain of the
power MOSFET). The OUTA/B (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 dri-
ves the positive (or high) side of the load. The output MOSFET
Undervoltage Lockout
The Undervoltage lockout (UVLO) prevents the output
MOSFET from being put into the ON state until the positive sup-
ply voltage, V , exceeds 2.5V. When the output switch is in the
IN
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.
source can be forced to a higher voltage than the drain (VOUT
>
VIN) when the output is OFF with little leakage current. If, how-
ever, VIN drops below 2.3V, reverse current may flow out the IN
pin regardless of the enable state. When the power switch is ON,
current can flow in either direction.
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, FLGA/B, 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
shutdown. The FLG output MOSFET is capable of sinking a
10mA load to typically 100mV above ground. Both flags may be
wire-NORed to a common pull-up resistor.
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
Cause
TJ > 135°C
VIN < 2.3V
FLG pin “0” Until
TJ ≤ 125°C
VIN > 2.5V
Switch State (FLG = “0”)
Turns OFF
Thermal Shutdown
Undervoltage Lockout (UVLO)
Current Limiting
Turns OFF
IO > 0.5A (step load)
Enable off or
Stays ON*
IO > 0.63A (ramped load)
Thermal Shutdown
* The switch and Fault Flag behavior during current-limiting is more complex than shown by this table. The detailed discussion on each of these
fault conditions gives additional information.
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