TPS2020, TPS2021, TPS2022, TPS2023, TPS2024

POWER-DISTRIBUTION SWITCHES

SLVS175A – DECEMBER 1998 – REVISED NOVEMBER 1999

18

POST OFFICE BOX 655303

APPLICATION INFORMATION

IN

OC

EN

GND

0.1

µF

2,3

5

4

6,7,8

0.1

µF

22

µF

Load

1

OUT

TPS2024

Power Supply

2.7 V to 5.5 V

10 k

Ω

Figure 38. Typical Application

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 and input pins 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

immediately switches into a constant-current output.

In the second condition, the excessive load occurs while the device is enabled. At the instant the excessive load

occurs, very high currents may flow for a short time before the current-limit circuit can react (see Figures 13–22).

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 Figures 7–11). The TPS202x is 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 can be connected

to the OC pin to reduce false overcurrent reporting. 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.