Datasheet

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APPLICATION INFORMATION
IN
OC
EN
GND
0.1 µF
2,3
5
4
6,7,8
0.1 µF 22 µF
Load
1
OUT
TPS2045A
Power Supply
2.7 V to 5.5 V
POWER-SUPPLY CONSIDERATIONS
OVERCURRENT
OC RESPONSE
TPS2045A , , TPS2046A
TPS2047A , TPS2048A , TPS2055A
TPS2056A , TPS2057A , TPS2058A
SLVS251C – SEPTEMBER 2000 – REVISED JANUARY 2008
Figure 24. Typical Application (Example, TPS2045A)
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 TPS204xA and TPS205xA sense the
short and immediately switch 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. 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 7). The TPS204xA and TPS205xA 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.
The OC open-drain output is asserted (active low) when an overcurrent or over temperature condition is
encountered. The output will remain asserted until the overcurrent or over temperature 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 TPS204xA and
TPS205xA family of devices are designed to reduce false overcurrent reporting. An internal overcurrent transient
filter eliminates the need for 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, also reducing erroneous overcurrent reporting.
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Product Folder Link(s): TPS2045A TPS2046A TPS2047A TPS2048A TPS2055A TPS2056A TPS2057A TPS2058A