9

Date: 5/25/04

SP6680 High Efficiency Buck/Boost Charge Pump Regulator

© Copyright 2004 Sipex Corporation

I

nput Voltage Ripple with Various Input, Output and Pump Capacitors

Looking at Tables 5, 6 & 7 it can be seen that increasing the value of the input capacitor (Table 5) reduces

the input voltage ripple the most. Note that placement of this input bypass capacitor as close to the

SP6680 input is recommended. Also note that Table 7 shows that increasing the pump capacitor beyond

the values of the other capacitors (2.2uF) actually increases the input ripple voltage and is not

recommended.

Table 5. Input 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)

Vin Ripple mV (pp)

Vin Ripple mV (pp)

0.47

296

30

1

140

24

2.2

80

18

4.7

36

12

10

24

10

22

14

6

Table 6. Input 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)

Vin Ripple mV (pp)

Vin Ripple mV (pp)

0.47

90

30

174

24

2.2

80

18

4.7

74

14

10

72

12

22

78

12

Table 7. Input 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)

Vin Ripple mV (pp)

Vin Ripple mV (pp)

0.47

76

26

176

20

2.2

80

18

4.7

154

16

10

162

16

22

162

14