After power is applied, the flying capacitor (C(fly)) connects alternately across the output capacitors C3 and CO.

This equalizes the voltage on those capacitors and draws current from VI to VO as required to maintain the

output at 1/2 VI.

The maximum input voltage between VI and GND in the schematic (or between IN and OUT at the device itself)

must not exceed 6.5 V.

TPS60400

OUT

C1+

IN

C1-

GND

1

2

3

5

4

C(fly)

1 µF

CO

1 µF

CI

1 µF

VO = VI/2

GND

VI

GND

C3

1 µF

Figure 9-6. TPS60400 as a High-Efficiency Rail Splitter

The application allows to generate a voltage rail at a level of -Vi as well as 2 x Vi (V(pos)).

In the circuit of Figure 9-7, capacitors CI, C(fly), and CO form the inverter, while C1 and C2 form the doubler. C1

and C(fly) are the flying capacitors; CO and C2 are the output capacitors. Because both the inverter and doubler

use part of the charge-pump circuit, loading either output causes both outputs to decline toward GND. Make sure

the sum of the currents drawn from the two outputs does not exceed 60 mA. The maximum output current at

V(pos) must not exceed 30 mA. If the negative output is loaded, this current must be further reduced.

TPS60400

OUT

C1+

IN

C1–

GND

1

2

3

5

4

C(fly)

1 µF

CO

1 µF

CI

1 µF

–VI

GND

GND

VI

C1

+

+

+

D2

C2

+

V(pos)

+

II ≈ –IO + 2 × IO(POS)

Figure 9-7. TPS60400 as Doubler/Inverter

The application generate a voltage rail at a level -2 x Vi.

Two devices can be cascaded to produce an even larger negative voltage (see Figure 9-8). The unloaded output

voltage is normally -2 × VI, but this is reduced slightly by the output resistance of the first device multiplied by the

quiescent current of the second. When cascading more than two devices, the output resistance rises

dramatically.

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TPS60400, TPS60401, TPS60402, TPS60403

SLVS324C – JULY 2001 – REVISED OCTOBER 2020

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