TPS60400, TPS60401, TPS60402, TPS60403

UNREGULATED 60-mA CHARGE PUMP VOLTAGE INVERTER

SLVS324 – JULY 2001

3

POST OFFICE BOX 655303

detailed description

operating principle

The TPS60400, TPS60401 charge pumps invert the voltage applied to their input. For the highest performance,

use low equivalent series resistance (ESR) capacitors (e.g., ceramic). During the first half-cycle, switches S2

C(fly)

1

µF

S2

S1

S3

S4

CO

1

µF

VO (–VI)

GND

VI

GND

Figure 1. Operating Principle

charge-pump output resistance

The TPS6040x devices are not voltage regulators. The charge pumps output source resistance is

approximately 15

droop toward GND as load current increases.

R

O [

1

ƒosc

C

(fly)

) 4 2R

SWITCH )

ESR

CFLY )

ESR

CO

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 IC’s internal functions, such as driving the

switches, oscillator, etc. These losses are affected by operating conditions such as input voltage, temperature,

and frequency. The next two losses are associated with the voltage converter circuit’s output resistance. 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:

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

P

1

2

C

(fly)

O

) 1

2

C

O

V

2

2V

O

V

RIPPLE

(1)

(2)