2525
AND
2535
USB
POWER CONTROL
SWITCHES
FUNCTIONAL DESCRIPTION
Power switch
The power switch is an N-channel MOSFET with a maximum
on-state resistance of 140 mΩ (V
IN
= 5 V). Configured as a
high-side switch, the power switch prevents current flow in
either direction if disabled. The drain body diode is discon-
nected from the source when the switch is OFF allowing the
output voltage to exceed the input voltage without causing
current conduction. The power switch supplies a minimum of
500 mA per switch.
Charge pump
An internal charge pump supplies power to the driver circuit
and provides the necessary voltage to pull the gate of the
MOSFET above the source. The charge pump operates from
input voltages as low as 2.7 V. The charge pump is limited to
2.5
µA
to establish a controlled turn on time of typically 1 ms.
Driver
The driver controls the gate voltage of the power switch. To
limit large current surges and reduce the associated electromag-
netic interference (EMI) produced, the driver incorporates
circuitry that controls the rise times and fall times of the output
voltage. The rise time is typically 1 ms.
ENABLE (EN or EN)
The logic enable disables the power switch and the bias for the
charge pump, driver, and other circuitry to reduce the supply
current to less than 5
µA
maximum when a logic high is present
on EN (A2525) or a logic low is present (A2535). The proper
logic level restores bias to the drive and control circuits and
turns the power ON. The enable input is a compatible with both
TTL and CMOS logic levels.
Fault Flag (FLG)
This open drain output is asserted (active low) when an
overcurrent or over temperature condition is encountered. The
output will remain asserted until the overcurrent or over
temperature condition is removed.
Current sense
A sense FET monitors the current supplied to the load. The
sense FET measures current more efficiently than conventional
resistance methods. When an overload or short circuit is
encountered, the current-sense circuitry sends a control signal to
the driver. The driver in turn reduces the gate voltage and
drives the power FET into its saturation region, which switches
the output into a constant-current mode and holds the current
constant while varying the voltage on the load.
Thermal sense
An internal thermal-sense circuit shuts off the power switch
when the junction temperature rises to approximately 165°C.
Hysteresis is built into the thermal sense circuit. After the
device has cooled approximately 10°C, the switch turns back
ON. The switch continues to cycle off and on until the fault is
removed.
Undervoltage lockout
A voltage-sense circuit monitors the input voltage. When the
input voltage is approximately 2 V, a control signal turns OFF
the power switch.
4
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
