TC7660HCPA datasheet(5/8 Pages) MICROCHIP

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HIGH FREQUENCY 7660 DC-TO-DC

VOLTAGE CONVERTER

TC7660H

TC7660H-2 10/1/96

DS21466A

Figure 5. Paralleling Devices Lowers Output Impedance

TC7660H

"n"

"1"

TC7660H

V +

CMOS

GATE

1.0

µF

VOUT

1.0

µF

1 k

Ω

V +

Figure 6. External Clocking

Figure 7. Positive Voltage Multiplier

Positive Voltage Multiplication

The TC7660H may be employed to achieve positive

voltage multiplication using the circuit shown in Figure 7. In

this application, the pump inverter switches of the TC7660H

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 10mA, it will be approximately 60

Ω.

Combined Negative Voltage Conversion

and Positive Supply Multiplication

Figure 8 combines the functions shown in Figures 3 and

8 to provide negative voltage conversion and positive volt-

age 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 multi-

plied 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.

V +

VOUT =

(2 V +) – (2 VF)

VOUT =

– (V+– VF)

TC7660H

Figure 8. Combined Negative Converter and Positive Multiplier

V+

VOUT =

(2 V+) – (2 VF)

TC7660H

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