SCHOTTKY DIODE SELECTION

COMPENSATION CAPACITOR SELECTION

INPUT AND OUTPUT CAPACITOR SELECTION

Fs

V

ripple

(6)

V

R

ESR

TPS61160A

TPS61161A

TPS61160A/61A has built-in slope compensation to avoid sub-harmonic oscillation associated with current mode

control. If the inductor value is lower than 10

µH, the slope compensation may not be adequate, and the loop can

be unstable. Therefore, customers need to verify the inductor in their application if it is different from the

recommended values.

Table 1. Recommended Inductors for TPS61160A/61A

L

DCR MAX

SATURATION CURRENT

SIZE

PART NUMBER

VENDOR

(

µH)

(

Ω)

(mA)

(L × W × H mm)

LQH3NPN100NM0

10

0.3

750

3×3×1.5

Murata

VLCF5020T-220MR75-1

22

0.4

750

5×5×2.0

TDK

CDH3809/SLD

10

0.3

570

4×4×1.0

Sumida

A997AS-220M

22

0.4

510

4×4×1.8

TOKO

The high switching frequency of the TPS61160A/61A demands a high-speed rectification for optimum efficiency.

Ensure that the diode average and peak current rating exceeds the average output current and peak inductor

current. In addition, the diode’s reverse breakdown voltage must exceed the open LED protection voltage. The

ONSemi MBR0540 and the ZETEX ZHCS400 are recommended for TPS61160A/61A.

The compensation capacitor C3 (see the block diagram), connected from COMP pin to GND, is used to stabilize

the feedback loop of the TPS61160A/61A. Use a 220nF ceramic capacitor for C3.

The output capacitor is mainly selected to meet the requirements for the output ripple and loop stability. This

ripple voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a

capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated by

using:

Due to its low ESR, Vripple_ESR can be neglected for ceramic capacitors, but must be considered if tantalum or

electrolytic capacitors are used.

Care must be taken when evaluating a ceramic capacitor’s derating under dc bias, aging and AC signal. For

example, larger form factor capacitors (in 1206 size) have a resonant frequencies in the range of the switching

frequency. So the effective capacitance is significantly lower. The DC bias can also significantly reduce

capacitance. Ceramic capacitors can loss as much as 50% of its capacitance at its rated voltage. Therefore,

leave the margin on the voltage rating to ensure adequate capacitance at the required output voltage.

The capacitor in the range of 1

µF to 4.7µF is recommended for input side. The output requires a capacitor in the

range of 0.47

µF to 10µF. The output capacitor affects the loop stability of the boost regulator. If the output

capacitor is below the range, the boost regulator can potentially become unstable. For example, if use the output

capacitor of 0.1

µF, a 470nF compensation capacitor has to be used for the loop stable.

The popular vendors for high value ceramic capacitors are:

TDK (http://www.component.tdk.com/components.php)

Murata (http://www.murata.com/cap/index.html)

Copyright © 2009, Texas Instruments Incorporated

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Product Folder Link(s): TPS61160A TPS61161A