AT1380A

Preliminary Product Information

Switching Regulator Controller for LCD Bias

2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.

Tel: 886-3-563-0878

Fax: 886-3-563-0879

9

Setting Oscillating Frequency

The oscillator circuit generates a triangular sawtooth wave with a peak of 0.8V and a trough of 0.1V

using the timing capacitor (CT) and the timing resistor (RT) that are connected to the OSC pin. This

oscillator can provide oscillating frequency in the range from 20KHz to 1MHz. The waveform of the

OSC pin is shown as Figure 2.

Figure 2 Oscillator Waveform

The cycle (T) can be determined as follows:

Switching Regulator Function

(1) Reference voltage circuit

A temperature-compensated reference voltage (~1.25V) is generated by the reference voltage

circuit from the voltage supplied by the power supply pin (pin 3). The circuit also sets the idle

period besides providing the reference voltage for the switching regulator.

(2) Error amplifier

The error amplifier detects the output voltage of the switching regulator and sets the PWM

control signal. The voltage gain is fixed. The system is made stable by connecting a phase

compensation capacitor to the FB pin (pin 8).

(3) PWM comparator

The voltage comparator includes one inverting and three non-inverting inputs. The comparator is

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