4-72

TELCOM SEMICONDUCTOR, INC.

TC7660S

SUPER CHARGE PUMP DC-TO-DC

VOLTAGE CONVERTER

The output characteristics of the circuit in Figure 3 are

those of a nearly ideal voltage source in series with 70

Ω.

Thus, for a load current of –10mA and a supply voltage of

+5V, the output voltage would be –4.3V.

The dynamic output impedance of the TC7660S is due,

primarily, to capacitive reactance of the charge transfer

output for only 1/2 of the cycle, the equation is:

Paralleling Devices

Any number of TC7660S voltage converters may be

paralleled to reduce output resistance (Figure 4). The reser-

resistance would be approximately:

2

2

= 3.18

Ω,

Figure 4. Paralleling Devices Lowers Output Impedance

Dos and Don'ts

• Do not exceed maximum supply voltages.

• Do not connect the LV terminal to GND for supply

voltages greater than 3.5V.

• Do not short circuit the output to V

above 5.5V for extended periods; however, transient

conditions including start-up are okay.

• When using polarized capacitors in the inverting mode,

to GND.

Simple Negative Voltage Converter

Figure 3 shows typical connections to provide a nega-

tive supply where a positive supply is available. A similar

scheme may be employed for supply voltages anywhere in

the operating range of +1.5V to +12V, keeping in mind that

pin 6 (LV) is tied to the supply negative (GND) only for supply

voltages below 3.5V.

Figure 3. Simple Negative Converter

1

2

3

4

8

7

6

5

TC7660S

V

+

1

2

3

4

8

7

6

5

TC7660S

C1

RL

C2

C1

"n"

"1"

+

1

2

3

4

8

7

6

5

TC7660S

10µF

+

V

+

10µF

+

NOTES:

*

C1

C2

n (number of devices)