8.3 Feature Description

8.3.1 Charge-Pump Output Resistance

The TPS6040x devices are not voltage regulators. The charge pump's output source resistance is approximately

15 Ω at room temperature (with VI = 5 V), and VO approaches -5 V when lightly loaded. VO droops toward GND

as load current increases.

VO = –(VI – RO × IO)

(1)

R

O [

1

ƒ

osc

C

(fly)

) 4 2RSWITCH ) ESRCFLY ) ESRCO

RO = output resistance of the converter

(2)

8.3.2 Efficiency Considerations

The power efficiency of a switched-capacitor voltage converter is affected by three factors: the internal losses in

the converter IC, the resistive losses of the capacitors, and the conversion losses during charge transfer

between the capacitors. The internal losses are associated with the internal functions of the IC, such as driving

the switches, oscillator, and so forth. These losses are affected by operating conditions such as input voltage,

temperature, and frequency. The next two losses are associated with the output resistance of the voltage

converter circuit. Switch losses occur because of the on-resistance of the MOSFET switches in the IC. Charge-

pump capacitor losses occur because of their ESR. The relationship between these losses and the output

resistance is as follows:

PCAPACITOR LOSSES + PCONVERSION LOSSES = IO2 × RO

RSWITCH = resistance of a single MOSFET-switch inside the converter

fOSC = oscillator frequency

(3)

The first term is the effective resistance from an ideal switched-capacitor circuit. Conversion losses occur during

the charge transfer between C(fly) and CO when there is a voltage difference between them. The power loss is:

P

CONV.LOSS +

1

2

C

(fly) V

2

I *

V 2

O

)

1

2

C

O V

2

RIPPLE *

2V

OVRIPPLE

ƒosc

(4)

The efficiency of the TPS6040x devices is dominated by their quiescent supply current at low output current and

by their output impedance at higher current.

h

^

I

O

I

O )

I

Q

1 *

I

O

R

O

V

I

(5)

Where, IQ = quiescent current.

www.ti.com

TPS60400, TPS60401, TPS60402, TPS60403

SLVS324C – JULY 2001 – REVISED OCTOBER 2020

Copyright © 2020 Texas Instruments Incorporated

Submit Document Feedback

11

Product Folder Links: TPS60400 TPS60401 TPS60402 TPS60403