TPS2047, TPS2057

TRIPLE CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

SLVS194 – APRIL 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 IN 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 VI(INx) has been applied (see Figure 6). The TPS2047 and TPS2057 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 TPS2047 and TPS2057 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 OCx 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.