LTC1144 datasheet(8/12 Pages) LINER

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LTC1144

1144fa

For more information www.linear.com/LTC1144

Typical applicaTions

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

56Ω resistor. The 56Ω 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

Ultra-Precision Voltage Divider

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

At an oscillator frequency of 10kHz and C1 = 10µF, the

first term is:

REQUIV =

fOSC /2

(

)×C1

×103 ×10×10−6

= 20Ω

Notice that the above equation for REQUIV is not a capaci-

tive reactance equation (XC = 1/ωC) and does not contain

a 2π 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 = 10µF, the output imped-

ance goes from 56Ω at fOSC = 10kHz to 250Ω at fOSC =

1kHz. As the 1/(f

× C) term becomes large compared 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

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 cir-

cuit 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).

Figure 11. Battery Splitter

10µF

V+

2V TO 18V

VOUT = –V+

TMIN ≤ TA ≤ TMAX

1144 F08

LTC1144

VIN

2V TO 18V

VOUT = 2(VIN – 1)

10µF

1N4148

1144 F09

LTC1144

10µF

V+

4V TO 36V

1144 F10

LTC1144

±0.002%

TMIN ≤ TA ≤ TMAX

IL ≤ 100nA

V+

10µF

OUTPUT

COMMON

VB/2

–VB/2

–9V

1144 F11

LTC1144

18V

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