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MC7660

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Figure 5. Increased Output Voltage by Cascading Devices

MC7660

V+

MC7660

VOUT*

*NOTE:

VOUT = –n V+ for 1.5 V ≤ V+ ≤ 10 V

“1”

“n”

Figure 6. External Clocking

MC7660

V+

VOUT

V+

1 k

CMOS

GATE

Figure 7. Lowering Oscillator Frequency

MC7660

V+

VOUT

COSC

Positive Voltage Multiplication

The MC7660 may be employed to achieve positive

voltage multiplication using the circuit shown in Figure 8.

In this application, the pump inverter switches of the

MC7660 are used to charge C1 to a voltage level of V+ – VF

(where V+ is the supply voltage and VF is the forward voltage

drop of diode D1). On the transfer cycle, the voltage on C1

plus the supply voltage (V+) is applied through diode D2 to

capacitor C2. The voltage thus created on C2 becomes (2 V+)

– (2 VF), or twice the supply voltage minus the combined

forward voltage drops of diodes D1 and D2.

The source impedance of the output (VOUT) will depend on

the output current, but for V+ = 5V and an output current of

10 mA, it will be approximately 60

Figure 8. Positive Voltage Multiplier

MC7660

V+

VOUT =

(2 V+) – (2 VF)

Combined Negative Voltage Conversion and Positive

Supply Multiplication

Figure 9 combines the functions shown in Figures 3 and

8 to provide negative voltage conversion and positive

voltage multiplication simultaneously. This approach would

be, for example, suitable for generating +9V and –5V from

an existing +5V supply. In this instance, capacitors C1 and

C3 perform the pump and reservoir functions, respectively,

for the generation of the negative voltage, while capacitors

C2 and C4 are pump and reservoir, respectively, for the

multiplied positive voltage. There is a penalty in this

configuration which combines both functions, however, 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 9. Combined Negative Converter and

Positive Muliplier

MC7660

V+

VOUT =

–(V+ – VF)

VOUT =

(2 V+) – (2 VF)

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