TPS60400, TPS60401, TPS60402, TPS60403

UNREGULATED 60mA CHARGE PUMP VOLTAGE INVERTER

SLVS324A − JULY 2001 REVISED NOVEMBER 2004

4

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efficiency considerations (continued)

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

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.

Increasing the output capacitor’s size reduces the output ripple voltage. Decreasing its ESR reduces both output

resistance and ripple. Smaller capacitance values can be used with light loads if higher output ripple can be

tolerated. Use the following equation to calculate the peak-to-peak ripple.

V

O(ripple) +

I

O

fosc

Co

) 2

I

O

ESR

CO

Table 1. Recommended Capacitor Values

DEVICE

VI

[V]

IO

[mA]

[

µF]

C(fly)

[

µF]

CO

[

µF]

TPS60400

1.8

…5.5

60

1

1

1

TPS60401

1.8

…5.5

60

10

10

10

TPS60402

1.8

…5.5

60

3.3

3.3

3.3

TPS60403

1.8

…5.5

60

1

1

1