Datasheet

TPS22934
SLVSAD4A –AUGUST 2010–REVISED JUNE 2013 www.ti.com
APPLICATION INFORMATION
ON/OFF Control
The ON pin controls the state of the switch. The TPS22934 has built-in hysteresis on its control inputs. The load
switch is active when the ON voltage is greater than the positive going voltage threshold (V
TH+
). If the ON voltage
is lower than the negative going voltage threshold (V
TH-
), then the pass FET is deactivated and the active
pulldown from VOUT to GND is activated.
This is ideal for power rail sequencing applications as shown in Figure 3 where the 2.8-V supply needs to be
valid before the 1.8-V supply turn on:
Figure 3. 1.8-V / 2.8-V Power Rail Sequencing
Input Capacitor
To limit the voltage drop on the input supply caused by transient in-rush currents when the switch turns on into a
discharged load capacitor or short-circuit, a capacitor needs to be placed between VIN and GND. A 1-µF ceramic
capacitor, C
IN
, placed close to the pins is usually sufficient. Higher values of C
IN
can be used to further reduce
the voltage drop.
Output Capacitor
Due to the integral body diode in the PMOS switch, a C
IN
greater than C
L
is highly recommended. A C
L
greater
than C
IN
can cause V
OUT
to exceed V
IN
when the system supply is removed. This could result in current flow
through the body diode from V
OUT
to V
IN
.
Board Layout
For best performance, all traces should be as short as possible. To be most effective, the input and output
capacitors should be placed close to the device to minimize the effects that parasitic trace inductances may have
on normal and short-circuit operation. Using wide traces for V
IN
, V
OUT
, and GND helps minimize the parasitic
electrical effects along with minimizing the case to ambient thermal impedance.
Undervoltage Lockout
The undervoltage lockout turns off the switch if the input voltage drops below the under-voltage lockout
threshold. With the ON pin active, the input voltage rising above the undervoltage lockout threshold causes a
controlled turn-on of the switch, which limits current overshoots.
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