TPS2045_14 Datasheet, PDF (15/25 Pages) Texas Instruments – CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

TPS2045, TPS2055
CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES
APPLICATION INFORMATION
SLVS182 – APRIL 1999
overcurrent
A sense FET is employed to check 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(IN) has been applied (see Figure 6). The TPS2045 and TPS2055 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 TPS2045 and TPS2055 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.
OC response
The OC open-drain output is asserted (active low) when an overcurrent or overtemperature condition is
encountered. The output will remain asserted until the overcurrent or overtemperature condition is removed.
Connecting a heavy capacitive load to an enabled device can cause momentary false overcurrent reporting from
the inrush current flowing through the device, charging the downstream capacitor. An RC filter of 500 µs (see
Figure 30) can be connected to the OC pin to reduce false overcurrent reporting caused by hot-plug switching
events or extremely high capacitive loads. Using low-ESR electrolytic capacitors on the output lowers the inrush
current flow through the device during hot-plug events by providing a low impedance energy source, thereby
reducing erroneous overcurrent reporting.
TPS2045
GND
IN
IN
EN
OUT
OUT
OUT
OC
V+
Rpullup
TPS2045
GND
IN
IN
EN
OUT
OUT
OUT
OC
V+
Rpullup
Rfilter
To USB
Controller
Cfilter
Figure 30. Typical Circuit for OC Pin and RC Filter for Damping Inrush OC Responses
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