8

FN3072.7

October 10, 2005

Typical Applications

Simple Negative Voltage Converter

The majority of applications will undoubtedly utilize the ICL7660

and ICL7660A for generation of negative supply voltages.

Figure 13 shows typical connections to provide a negative

supply negative (GND) for supply voltages below 3.5V.

The output characteristics of the circuit in Figure 13A can be

approximated by an ideal voltage source in series with a

resistance as shown in Figure 13B. The voltage source has

the ON resistance of the internal MOS switches (shown in

and the ESR (equivalent series resistance) of C1 and C2. A

RSW, the total switch resistance, is a function of supply

voltage and temperature (See the Output Source Resistance

graphs), typically 23

Ω at 25°C and 5V. Careful selection of

output impedance. High value capacitors will reduce the

lower the ESR term. Increasing the oscillator frequency will

there is no longer enough time to fully charge the capacitors

FIGURE 14. OUTPUT RIPPLE

FIGURE 15. PARALLELING DEVICES

FIGURE 16. CASCADING DEVICES FOR INCREASED OUTPUT VOLTAGE

A

B

0

-(V+)

V

1

2

3

4

8

7

6

5

ICL7660

V+

ICL7660A

1

2

3

4

8

7

6

5

ICL7660

ICL7660A

+

-

“n”

“1”

1

2

3

4

8

7

6

5

V+

1

2

3

4

8

7

6

5

+

-

10

µF

+

-

10

µF

+

-

10

µF

+

-

10

µF

ICL7660

ICL7660A

“n”

ICL7660

ICL7660A

“1”

1

2

1

ICL7660, ICL7660A