LM828

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SNOS035D – MARCH 2010 – REVISED MAY 2013

Pin Functions

PIN DESCRIPTIONS

Pin

Name

Function

1

OUT

Negative voltage output.

2

V+

Power supply positive input.

3

CAP

−

Connect this pin to the negative terminal of the charge-pump capacitor.

4

GND

Power supply ground input.

5

CAP+

Connect this pin to the positive terminal of the charge-pump capacitor.

Circuit Description

The LM828 contains four large CMOS switches which are switched in a sequence to invert the input supply

voltage. Energy transfer and storage are provided by external capacitors. Figure 12 illustrates the voltage

switches and the ESR of the capacitors) and the charge transfer loss between capacitors.

Figure 12. Voltage Inverting Principle

Application Information

SIMPLE NEGATIVE VOLTAGE CONVERTER

The main application of LM828 is to generate a negative supply voltage. The voltage inverter circuit uses only

two external capacitors as shown in the Basic Application Circuits. The range of the input supply voltage is 1.8V

to 5.5V.

The output characteristics of this circuit can be approximated by an ideal voltage source in series with a

resistance. The voltage source equals

charging and discharging at a current approximately equal to the output current, therefore, this ESR term only

(1)

High capacitance, low ESR capacitors will reduce the output resistance.

The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the

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