TPS60400Q1, TPS60401Q1, TPS60402Q1, TPS60403Q1

UNREGULATED 60mA CHARGE PUMP VOLTAGE INVERTER

SGLS246A − JUNE 2004 − REVISED JUNE 2008

4

POST OFFICE BOX 655303

detailed description (continued)

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

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

I

Q

1

*

I

O

R

O

V

I

capacitor selection

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

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.

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

is loaded from IN to OUT, the circuit draws 2

capacitor is sufficient.

Increasing the flying capacitor’s size reduces the output resistance. Small values increases the output

resistance becomes dominated by the internal switch resistance and capacitor ESR.

(2)