PCF8591P datasheet(7/28 Pages) PHILIPS

7 / 28 page

2003 Jan 27

Philips Semiconductors

Product speciﬁcation

8-bit A/D and D/A converter

PCF8591

7.3

D/A conversion

The third byte sent to a PCF8591 device is stored in the

DAC data register and is converted to the corresponding

analog voltage using the on-chip D/A converter. This D/A

converter consists of a resistor divider chain connected to

the external reference voltage with 256 taps and selection

switches. The tap-decoder switches one of these taps to

the DAC output line (see Fig.6).

The analog output voltage is buffered by an auto-zeroed

unity gain amplifier. This buffer amplifier may be switched

on or off by setting the analog output enable flag of the

control register. In the active state the output voltage is

held until a further data byte is sent.

The on-chip D/A converter is also used for successive

approximation A/D conversion. In order to release the

DAC for an A/D conversion cycle the unity gain amplifier is

equipped with a track and hold circuit. This circuit holds the

output voltage while executing the A/D conversion.

The output voltage supplied to the analog output AOUT is

given by the formula shown in Fig.7. The waveforms of a

D/A conversion sequence are shown in Fig.8.

handbook, full pagewidth

MBL826

TAP

DECODER

R256

DAC out

R255

VREF

AGND

Fig.6 DAC resistor divider chain.

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