AN3535| Application Note
POWER-SUPPLY CIRCUITS
May 19, 2005
App Note 3535: Pushbuttons Control Regulated Switching Converter
Pushbutton control of a digital potentiometer enables this circuit to control the regulated output of a switching converter. Digitally controlled potentiometers (digipots) are useful for generating analog control voltages, but they usually operate under the direction of a microcontroller. Pushbutton control is simpler, but the digipot's inputs have no switch-debounce capability, and its up/down control is not particularly suitable for pushbuttons. Nor are such kinds of applications (pushbutton control of digipots) supported by application notes. Figure 1 illustrates the issues involved in wiring a digipot to a boost converter.
Figure 1. A digital potentiometer (IC1) and two pushbuttons (S1 and S2) let you adjust the regulated output voltage of this switching converter (IC2) in either direction. The digipot shown (IC1) has an end-to-end resistance of 100k . To increment the position of the wiper (W), pull the U/D pin high by depressing the U/D pushbutton (S2), and then pulse the INC input by pulsing pushbutton S1. Similarly, you decrement the wiper position by releasing S2
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