Datasheet
TPS2044, TPS2054
QUAD POWER-DISTRIBUTION SWITCHES
SLVS174B – JULY 1998 – REVISED FEBRUARY 1999
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
power-supply considerations
A 0.01-µF to 0.1-µF ceramic bypass capacitor between INx and GND, close to the device, is recommended.
Placing a high-value electrolytic capacitor on the output pin(s) is recommended when the output load is heavy.
This precaution reduces power-supply transients that may cause ringing on the input. Additionally, bypassing
the output with a 0.01-µF to 0.1-µF ceramic capacitor improves the immunity of the device to short-circuit
transients.
overcurrent
A sense FET checks for overcurrent conditions. Unlike current-sense resistors, sense FETs do not increase the
series resistance of the current path. When an overcurrent condition is detected, the device maintains a
constant output current and reduces the output voltage accordingly. Complete shutdown occurs only if the fault
is present long enough to activate thermal limiting.
Three possible overload conditions can occur. In the first condition, the output has been shorted before the
device is enabled or before V
I(INx)
has been applied (see Figure 6). The TPS2044 and TPS2054 sense the short
and immediately switch into a constant-current output.
In the second condition, the short occurs while the device is enabled. At the instant the short occurs, very high
currents may flow for a short time before the current-limit circuit can react. After the current-limit circuit has
tripped (reached the overcurrent trip threshhold) the device switches into constant-current mode.
In the third condition, the load has been gradually increased beyond the recommended operating current. The
current is permitted to rise until the current-limit threshold is reached or until the thermal limit of the device is
exceeded (see Figure 7). The TPS2044 and TPS2054 are capable of delivering current up to the current-limit
threshold without damaging the device. Once the threshold has been reached, the device switches into its
constant-current mode.