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Date: 5/25/04

SP6680 High Efficiency Buck/Boost Charge Pump Regulator

© Copyright 2004 Sipex Corporation

Output Voltage Ripple with Various Input, Output and Pump Capacitors

From Tables 8, 9 & 10 it appears that increasing pump capacitance will reduce output voltage ripple

the most. But, as we saw previously in Table 7, input voltage ripple increases with increasing pump

capacitance and it is not recommended to use pump capacitors greater than the other capacitor values.

It is therefore recommended to use an output capacitor value equal to or slightly above the pump

capacitor value. Note that for most designs the SP6680 output will be followed by a Low Dropout

Regulator that will greatly reduce the output ripple.

Table 8. Output Voltage Ripple vs Input Capacitance

All Ceramic Capacitors ESR < 0.05ohm

Cout, CF1, CF2 = 2.2uF, Iout = 5mA, CLK = 32kHz

Vin = 3.55V (In Regulation)

Vin = 3.85V (Not in Regulation)

Cin (uF)

Vout Ripple mV (pp)

Vout Ripple mV (pp)

0.47

9 0

5 2

19 2

5 2

2.2

104

5 2

4.7

102

5 2

10

106

52

22

108

52

Table 9. Output Voltage Ripple vs Output Capacitance

All Ceramic Capacitors ESR < 0.05ohm

Cin, CF1, CF2 = 2.2uF, Iout = 5mA, CLK = 32kHz

Vin = 3.55V (In Regulation)

Vin = 3.85V (Not in Regulation)

Cout (uF)

Vout Ripple mV (pp)

Vout Ripple mV (pp)

0.47

102

6 4

1

102

5 8

2.2

104

5 2

4.7

102

4 6

10

104

44

22

102

44

Table 10. Output Voltage Ripple vs Pump Capacitance

All Ceramic Capacitors ESR < 0.05ohm

Cin, Cout = 2.2uF, Iout = 5mA, CLK = 32kHz

Vin = 3.55V (In Regulation)

Vin = 3.85V (Not in Regulation)

CF1, CF2 (uF)

Vout Ripple mV (pp)

Vout Ripple mV (pp)

0.47

365

200

1

172

108

2.2

108

5 2

4.7

9 0

24

10

76

14

22

40

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