TC7660SVOA723 データシートの表示（PDF） - Microchip Technology

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TC7660SVOA723

Super Charge Pump DC-to-DC Voltage Converter

Microchip Technology 

5.6 Combined Negative Voltage

Conversion and Positive Supply

Multiplication

Figure 5-7 combines the functions shown in Figure 5-3

and Figure 5-6 to provide negative voltage conversion

and positive voltage multiplication simultaneously. For

example, this approach would be suitable for generat-

ing +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 pos-

itive 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+

1

8

2

7

3 TC7660S 6

+C1 4

5

+

C2

VOUT

= -V+

D1 + C3

VOUT =

D2 (2 V+) - (2 VF)

+

C4

FIGURE 5-7:

Combined Negative

Converter and Positive Multiplier.

5.7 Efficient Positive Voltage

Multiplication/Conversion

Since the switches that allow the charge pumping

operation are bidirectional, the charge transfer can be

performed backwards as easily as forwards.

Figure 5-8 shows a TC7660S transforming -5V to +5V

(or +5V to +10V, etc.). The only problem is that the

internal clock and switch-drive section will not operate

until some positive voltage has been generated. An ini-

tial inefficient pump, as shown in Figure 5-7, could be

used to start this circuit up, after which it will bypass the

other (D1 and D2 in Figure 5-7 would never turn on), or

else the diode and resistor shown dotted in Figure 5-8

can be used to “force” the internal regulator on.

TC7660S

VOUT = -V-

C1 +

10 µF

1

8

2

7

3 TC7660S 6

4

5

1 M

V- input

+

10 µF

FIGURE 5-8:

Conversion.

Positive Voltage

5.8 Voltage Splitting

The same bidirectional characteristics used in

Figure 5-8 can also be used to split a higher supply in

half, as shown in Figure 5-9. The combined load will be

evenly shared between the two sides. Once again, a

high value resistor to the LV pin ensures start-up.

Because the switches share the load in parallel, the

output impedance is much lower than in the standard

circuits, and higher currents can be drawn from the

device. By using this circuit, and then the circuit of

Figure 5-3, +15V can be converted (via +7.5V and -7.5V)

to a nominal -15V, though with rather high series

resistance (~250Ω).

+

RL1

50μF

VOUT =

V + –V –

2

RL2

50μF

+

–

100 kΩ

+

50μF

–

V+

1

8

2

7

1 MΩ

3 TC7660S 6

4

5

V–

FIGURE 5-9:

Splitting a Supply in Half.

5.9 Negative Voltage Generation for

Display ADCs

The TC7106 is designed to work from a 9V battery.

With a fixed power supply system, the TC7106 will

perform conversions with input signal referenced to

power supply ground.

5.10 Negative Supply Generation for

4½ Digit Data Acquisition System

The TC7135 is a 4½ digit ADC operating from ±5V

supplies. The TC7660S provides an inexpensive -5V

source. (See AN16 and AN17 for TC7135 interface

details and software routines.)

 2001-2015 Microchip Technology Inc.

DS20001467C-page 11

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