7

LTC1144

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

S

APPLICATI

TYPICAL

Negative Voltage Converter

Figure 8 shows a typical connection which will provide a

negative supply from an available positive supply. This

circuit operates over full temperature and power supply

ranges

without the need of any external diodes.

The output voltage (pin 5) characteristics of the circuit are

those of a nearly ideal voltage source in series with a 56

Ω

resistor. The 56

Ω output impedance is composed of two

terms: 1) the equivalent switched capacitor resistance

(see Theory of Operation), and 2) a term related to the on-

resistance of the MOS switches.

Figure 9. Voltage Doubler

1

2

3

4

8

7

6

5

+

+

+

+

2V TO 18V

10

µF10µF

1N4148

1N4148

1144 F09

LTC1144

Ultra-Precision Voltage Divider

An ultra-precision voltage divider is shown in Figure 10. To

achieve the 0.0002% accuracy indicated, the load current

should be kept below 100nA. However, with a slight loss

in accuracy, the load current can be increased.

At an oscillator frequency of 10kHz and C1 = 10

µF, the first

term is:

R

fC

EQUIV

OSC

−

1

21

1

510

10 10

20

36

/

Ω

a 2

π term.

The exact expression for output impedance is extremely

complex, but the dominant effect of the capacitor is clearly

shown in Figure 5. For C1 = C2 = 10

µF, the output

impedance goes from 56

to the switch on-resistance term, the output resistance is

determined by 1/(f

× C) only.

Voltage Doubling

Figure 9 shows a two-diode capacitive voltage doubler.

With a 15V input, the output is 29.45V with no load and

28.18V with a 10mA load.

Figure 8. Negative Voltage Converter

1

2

3

4

8

7

6

5

+

10

µF

10

µF

2V TO 18V

+

1144 F08

LTC1144

1

2

3

4

8

7

6

5

+

+

C2

10

µF

C1

10

µF

4V TO 36V

1144 F10

LTC1144

±0.002%

V+

2

Figure 10. Ultra-Precision Voltage Divider

Battery Splitter

A common need in many systems is to obtain (+) and (–)

supplies from a single battery or single power supply

system. Where current requirements are small, the circuit

shown in Figure 11 is a simple solution. It provides

symmetrical

± output voltages, both equal to one half the

input voltage. The output voltages are both referenced to

pin 3 (output common).

1

2

3

4

8

7

6

5

+

C2

10

µF

C1

10

µF

OUTPUT

COMMON

9V

–9V

1144 F11

LTC1144

18V

+

Figure 11. Battery Splitter