7

LTC1044A

Capacitor Selection

External capacitors C1 and C2 are not critical. Matching

is not required, nor do they have to be high quality or

tight tolerance. Aluminum or tantalum electrolytics are

excellent choices with cost and size being the only

consideration.

Negative Voltage Converter

Figure 6 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 LV

≥ 3V it may be

“floated”, since LV is internally switched to ground (pin 3)

≥ 3V.

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

those of a nearly ideal voltage source in series with an 80

Ω

resistor. The 80

Ω output impedance is composed of two

terms:

1. The equivalent switched-capacitor resistance (see

Theory of Operation).

2. A term related to the on-resistance of the MOS

switches.

At an oscillator frequency of 10kHz and C1 = 10

µF, the first

term is:

=

= 20

Ω

1

1

5

a 2

π term.

Figure 6. Negative Voltage Converter

The exact expression for output resistance is extremely

complex, but the dominant effect of the capacitor is clearly

shown on the typical curves of Output Resistance and

Power Efficiency vs Frequency. For C1 = C2 = 10

µF, the

output impedance goes from 60

compared to the switch-on resistance term, the output

resistance is determined by 1/(f

× C) only.

Voltage Doubling

Figure 7 shows a two-diode capacitive voltage doubler.

With a 5V input, the output is 9.93V with no load and 9.13V

with a 10mA load. With a 10V input, the output is 19.93V

with no load and 19.28V with a 10mA load.

1

2

3

4

8

7

6

5

LTC1044A

(1.5V TO 12V)

1N5817

1N5817

REQUIRED

LTC1044A • F07

+

+

+

+

10

µF10µF

Figure 7. Voltage Doubler

Ultra-Precision Voltage Divider

An ultra-precision voltage divider is shown in Figure 8. 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.

Figure 8. Ultra-Precision Voltage Divider

1

2

3

4

8

7

6

5

LTC1044A

+

+

10

µF

10

µF

LTC1044A • F06

1

2

3

4

8

7

6

5

LTC1044A

+

C1

10

µF

+

C2

10

µF

REQUIRED FOR

LTC1044A • F08

S

APPLICATI

I FOR ATIO