APPLICATION INFORMATION

INPUT AND OUTPUT CAPACITANCE

PROGRAMMING THE CURRENT-LIMIT THRESHOLD

0.94

ILIM

0.977

ILIM

1.016

ILIM

22980V

OSmax

R

k

23950V

OSnom

R

k

25230V

OSmin

R

k

I

(mA) =

I

(mA) =

I

(mA) =

W

W

W

(1)

TPS2552

TPS2553, TPS2552-1, TPS2553-1

Input and output capacitance improves the performance of the device; the actual capacitance should be

optimized for the particular application. For all applications, a 0.1

µF or greater ceramic bypass capacitor between

IN and GND is recommended as close to the device as possible for local noise de-coupling. This precaution

reduces ringing on the input due to power-supply transients. Additional input capacitance may be needed on the

input to reduce voltage overshoot from exceeding the absolute maximum voltage of the device during heavy

transient conditions. This is especially important during bench testing when long, inductive cables are used to

connect the evaluation board to the bench power-supply.

Placing a high-value electrolytic capacitor on the output pin is recommended when large transient currents are

expected on the output. Additionally, bypassing the output with a 0.01

µF to 0.1 µF ceramic capacitor improves

the immunity of the device to transient conditions and noise.

The overcurrent threshold is user programmable via an external resistor. The TPS2552/53 and TPS2552-1/53-1

use an internal regulation loop to provide a regulated voltage on the ILIM pin. The current-limit threshold is

232 k

Ω to ensure stability of the internal regulation loop. Many applications require that the minimum current limit

is above a certain current level or that the maximum current limit is below a certain current level, so it is

equations and Figure 24 can be used to calculate the resulting overcurrent threshold for a given external resistor

However, the equations do not account for tolerance due to external resistor variation, so it is important to

TPS2552-1/53-1 should be as short as possible to reduce parasitic effects on the current-limit accuracy.

below a maximum load current.

minimum threshold is important to ensure start up into full load or heavy capacitive loads. The resulting maximum

maximum threshold is important to avoid current limiting upstream power supplies causing the input voltage bus

where 19.1 k

While the maximum recommended value of RILIM is 232 k

Ω, there is one additional configuration that allows for

a lower current-limit threshold. The ILIM pin may be connected directly to IN to provide a 75 mA (typ) current-limit

threshold. Additional low-ESR ceramic capacitance may be necessary from IN to GND in this configuration to

prevent unwanted noise from coupling into the sensitive ILIM circuitry.

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): TPS2552 TPS2553 TPS2552-1 TPS2553-1