9 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification, and TI

does not warrant its accuracy or completeness. TI’s customers are responsible for determining

suitability of components for their purposes. Customers should validate and test their design

implementation to confirm system functionality.

9.1 Application Information

The TPS6040x is a family of devices that generate an unregulated negative output voltage from an input voltage

ranging from 1.6 V to 5.5 V.

9.2 Typical Application

9.2.1 Voltage Inverter

The design guidelines provide a component selection to operate the device within the recommended operating

conditions.

TPS60400

C1–

C1+

3

5

OUT

IN

GND

1

2

4

CI

1 µF

CO

1 µF

–5 V,

Max 60 mA

Input 5 V

C(fly)

1 µF

Figure 9-1. Typical Operating Circuit

9.2.1.1 Design Requirements

The TPS6040x is connected to generate a negative output voltage from a positive input.

9.2.1.2 Detailed Design Procedure

The most common application for these devices is a charge-pump voltage inverter (see Figure 9-1). This

application requires only two external components; capacitors C(fly) and CO, plus a bypass capacitor, if

necessary. Refer to the capacitor selection section for suggested capacitor types.

For the maximum output current and best performance, three ceramic capacitors of 1 µF (TPS60400,

TPS60403) are recommended. For lower currents or higher allowed output voltage ripple, other capacitors can

also be used. It is recommended that the output capacitors has a minimum value of 1 µF. With flying capacitors

lower than 1 µF, the maximum output power decreases.

9.2.1.2.1 Capacitor Selection

To maintain the lowest output resistance, use capacitors with low ESR (see Table 9-1). The charge-pump output

resistance is a function of C(fly)'s and CO's ESR. Therefore, minimizing the charge-pump capacitor's ESR

minimizes the total output resistance. The capacitor values are closely linked to the required output current and

the output noise and ripple requirements. It is possible to only use 1-µF capacitors of the same type.

9.2.1.2.2 Input Capacitor (CI)

Bypass the incoming supply to reduce its ac impedance and the impact of the TPS6040x switching noise. The

recommended bypassing depends on the circuit configuration and where the load is connected. When the

inverter is loaded from OUT to GND, current from the supply switches between 2 x IO and zero. Therefore, use a

large bypass capacitor (for example, equal to the value of C(fly)) if the supply has high ac impedance. When the

inverter is loaded from IN to OUT, the circuit draws 2 × IO constantly, except for short switching spikes. A 0.1-µF

bypass capacitor is sufficient.

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TPS60400, TPS60401, TPS60402, TPS60403

SLVS324C – JULY 2001 – REVISED OCTOBER 2020

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