Note

Choosing power switch with tighter current limit tolerance can loosen the up-stream power-supply

design.

9.2.2 Detailed Design Procedure

9.2.2.1 Step-by-Step Design Procedure

To begin the design process a few parameters must be decided upon. The designer must know the following:

• Normal input operation voltage

• Rating current

• Minimum current limit

• Maximum current limit

9.2.2.2 Input and Output Capacitance

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

optimized for the particular application. For all applications, a 0.1μF or greater ceramic bypass capacitor

between IN and GND is recommended as close to the device as possible for local noise decoupling. This

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

needed on the input to reduce voltage undershoot from exceeding the UVLO of other load share one power rail

with TPS2559 or 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.

Output capacitance is not required, but placing a high-value electrolytic capacitor on the output pin is

recommended when large transient currents are expected on the output to reduce the undershoot, which caused

by the inductance of the output power bus just after a short has occurred and the TPS2559 has abruptly reduced

OUT current. Energy stored in the inductance will drive the OUT voltage down and potentially negative as it

discharges.

9.2.2.3 Programming the Current-Limit Threshold

The overcurrent threshold is user programmable via an external resistor. The TPS2559 uses an internal

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

current sourced out of ILIM. The recommended 1% resistor range for R (ILIM) is 24.9 kΩ ≤ R(ILIM) ≤ 100 kΩ to

ensure stability of the internal regulation loop.

When ILIM pin short to GND (single point failure), maximum current limit is less than 8 A over temperature and

process variation.

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 important to consider the tolerance of the overcurrent

threshold when selecting a value for R (ILIM). The equations and the graph below can be used to estimate the

minimum and maximum variation of the current-limit threshold for a predefined resistor value within R (ILIM) is

24.9 kΩ ≤ R(ILIM) ≤ 100 kΩ. This variation is an approximation only and does not take into account, for example,

the resistor tolerance. For examples of more-precise variation of I OS refer to the current-limit section of the

Electrical Characteristics table.

OS max

1.0013

(ILIM)

OSnom

1.0008

(ILIM)

OS min

1.0010

(ILIM)

121635 V

I

(mA)

36

R

k

118079 V

I

(mA)

R

k

113325 V

I

(mA)

47

R

k

=

+

W

=

W

=

-

W

(1)

www.ti.com

TPS2559

SLVSCL5A – JUNE 2014 – REVISED NOVEMBER 2020

Copyright © 2020 Texas Instruments Incorporated

Submit Document Feedback

13

Product Folder Links: TPS2559