8

LTC660

Voltage Doubling

Figure 8 shows the LTC660 operating in the voltage

doubling mode. The external Schottky (1N5817) diode is

load. The diode has no effect on the output voltage.

1

2

3

4

8

7

6

5

BOOST

GND

LTC660 • F08

C1

150

µF

2.5V

TO 5.5V

LTC660

1N5817*

OSC

LV

C2

150

µF

* SCHOTTKY DIODE IS FOR START-UP ONLY

+

+

Figure 8. Voltage Doubler

Negative Voltage Converter

Figure 7 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 pin

≥ 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 a 6.5

Ω

resistor. The 6.5

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.

At an oscillator frequency of 10kHz and C1 = 150

µF, the

first term is:

R=

1

f/2

EQUIV

OSC

()

=

=

C1

1

5 10

150 10

13

36

••

•

.

–

Ω.

2

π term.

The exact expression for output impedance is complex,

but the dominant effect of the capacitor is clearly shown on

the typical curves of output impedance and power effi-

ciency versus frequency. For C1 = C2 = 150

µF, the output

impedance goes from 6.5

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

determined by 1/fC only.

Ultraprecision Voltage Divider

An ultraprecision voltage divider is shown in Figure 9. To

achieve the 0.002% accuracy indicated, the load current

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

in accuracy, the load current can be increased.

1

2

3

4

8

7

6

5

BOOST

GND

C2

150

µF

LTC660 • F07

C1

150

µF

1.5V TO 5.5V

LTC660

OSC

LV

+

Figure 7. Voltage Inverter

Battery Splitter

A common need in many systems is to obtain positive and

negative supplies from a single battery or single power

supply system. Where current requirements are small, the

circuit shown in Figure 10 is a simple solution. It provides

symmetrical positive or negative output voltages, both

equal to one-half the input voltage. The output voltages are

both referenced to Pin 3 (Output Common).

Figure 9. Ultraprecision Voltage Divider

8

7

6

5

4

3

2

1

C1

150

µF

± 0.002%

3V TO 11V

LTC660 • F09

C2

150

µF

2

LTC660

+

+