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APPLICATION INFORMATION

POWER-SUPPLY CONSIDERATIONS

IN

OC1

EN1

OC2

2

8

5

7

0.1

µF

22

µF

0.1

µF

22

µF

Load

Load

OUT1

OUT2

Power Supply

2.7 V to 5.5 V

6

EN2

3

4

GND

0.1

µF

TPS2046B

1

OVERCURRENT

OC RESPONSE

TPS2045B, TPS2055B

TPS2046B, TPS2047B

SLVS532C – JULY 2004 – REVISED OCTOBER 2007

Figure 23. Typical Application (Example, TPS2046B)

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.

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 VI(IN) has been applied (see Figure 6). The TPS204xB/TPS2055B senses the short,

and immediately switches into a constant-current output.

In the second condition, a short or an overload occurs while the device is enabled. At the instant the overload

occurs, high currents may flow for a short period of time before the current-limit circuit can react. After the

current-limit circuit has tripped (reached the overcurrent trip threshold), 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. The TPS204xB/TPS2055B 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.

The OCx open-drain output is asserted (active low) when an overcurrent or overtemperature shutdown condition

is encountered after a 10-ms deglitch timeout. The output remains asserted until the overcurrent or

overtemperature condition is removed. Connecting a heavy capacitive load to an enabled device can cause a

momentary overcurrent condition; however, no false reporting on OCx occurs due to the 10-ms deglitch circuit.

The TPS204xB/TPS2055B is designed to eliminate false overcurrent reporting. The internal overcurrent deglitch

eliminates the need for external components to remove unwanted pulses. OCx is not deglitched when the switch

is turned off due to an overtemperature shutdown.

14

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