Datasheet

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APPLICATION INFORMATION

POWER-SUPPLY CONSIDERATIONS

OVERCURRENT

OC RESPONSES

TPS2080, TPS2081, TPS2082 DUAL

TPS2085, TPS2086, TPS2087 QUAD

SLVS202B – SEPTEMBER 2000 – REVISED OCTOBER 2007

Figure 24. Typical Application

A 0.01- μ F to 0.1- μ F 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- μ F to 0.1- μ F 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 V

I(IN)

has been applied (see Figure 6 ). The TPS208x 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, very high currents may flow for a short time before the current-limit circuit can react (see Figure 10 and

Figure 11 ). 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 (see Figure 8 ). The TPS208x 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 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. The TPS208x devices are

designed to reduce false overcurrent reporting. An internal overcurrent transient filter eliminates the need to use

external components to remove unwanted pulses. 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.

Product Folder Link(s): TPS2080, TPS2081, TPS2082 DUAL TPS2085, TPS2086, TPS2087 QUAD