4-12

TELCOM SEMICONDUCTOR, INC.

TC660

100mA CHARGE PUMP DC-TO-DC

VOLTAGE CONVERTER

Figure 8. Positive Voltage Doubler

Figure 9. Improved Voltage Doubler

1

2

3

4

8

7

6

5

R = 0.1 – 1M

Ω

C1

200

R

D

VOUT

= 2 VIN

VIN

C2

TC660

Figure 10. Combined Negative Converter and Positive Multiplier

Figure 9 shows an improved way of using the TC660 as

a voltage doubler.

reversal) through D. The optional 200

Ω resistor is only to

limit the brief latchup current.

startup.

Combined Negative Voltage Conversion

and Positive Supply Multiplication

Figure 10 combines the functions shown in Figures 3

and 8 to provide negative voltage conversion and positive

voltage multiplication simultaneously. In this instance, ca-

tions, respectively, for the generation of the negative volt-

respectively, for the multiplied positive voltage. There is a

penalty in this configuration in that the source impedances

of the generated supplies will be somewhat higher due to

the finite impedance of the common charge pump driver at

pin 2 of the device.

Figure 11. Positive Voltage Multiplier

1

2

3

4

8

7

6

5

+

V +

VOUT =

(2 V +) – (2 VF)

C1

D1

+

+

C3

C4

VOUT = –V

+

C2

TC660

D2

+

1

2

3

4

8

7

6

5

V+

VOUT =

(2 V+) – (2 VF)

+

C2

D1

D2

+

C1

TC660

Efficient Positive Voltage

Multiplication/Conversion

Since the switches that allow the charge pumping op-

eration are bidirectional, the charge transfer can be per-

formed backward as easily as forward. Figure 11 shows a

TC660 transforming –5V to +5V. The only problem here is

that the internal clock and switch-drive section will not

operate until some positive voltage has been generated. A

diode and resistor shown dotted in Figure 11 can be used to

"force" the internal regulator on.

1

2

3

4

8

7

6

5

+

VOUT = –V

–

150

µF

+

1 M

Ω

V– INPUT

C1

150

µF

TC660