9.3 System Examples

To reduce the output voltage ripple, a RC post filter can be used.

An output filter can easily be formed with a resistor (RP) and a capacitor (CP). Cutoff frequency is given by:

TPS60400

OUT

C1+

IN

C1–

GND

1

2

3

5

4

C(fly)

1 µF

CO

1 µF

CP

CI

1 µF

VO (–VI)

GND

VI

GND

RP

Figure 9-4. TPS60400 with RC-Post Filter

The equation refers only to the relation between output and input of the ac ripple voltages of the filter.

ƒc +

1

2pR

PCP

(1)

and ratio VO/VOUT is:

V

O

V

OUT

+

1

1 ) 2pƒRPCP

2

(2)

with RP = 50 Ω, CP = 0.1 µF and f = 250 kHz:

V

O

V

OUT

+ 0.125

(13)

To reduce the output voltage ripple, a LC post filter can be used.

Figure 9-5 shows a configuration with a LC-post filter to further reduce output ripple and noise.

TPS60400

OUT

C1+

IN

C1–

GND

1

2

3

5

4

C(fly)

1 µF

CO

1 µF

CP

CI

1 µF

VO (–VI)

GND

VI

GND

LP

VOUT

Figure 9-5. LC-Post Filter

The application allows to generate a voltage rail at a level of 1/2 of the input voltage.

A switched-capacitor voltage inverter can be configured as a high efficiency rail-splitter. This circuit provides a

bipolar power supply that is useful in battery powered systems to supply dual-rail ICs, like operational amplifiers.

Moreover, the SOT23-5 package and associated components require very little board space.

TPS60400, TPS60401, TPS60402, TPS60403

SLVS324C – JULY 2001 – REVISED OCTOBER 2020

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