Philips Semiconductors
Product specification
8-bit A/D and D/A converter
7.3
D/A conversion
PCF8591
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.
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
handbook, full pagewidth
VREF
R256
DAC out
R255
FF
D7
R3
D6
TAP
DECODER
D0
R1
AGND
00
MBL826
R2
02
01
Fig.6 DAC resistor divider chain.
2003 Jan 27
7
PHILIPS [ NXP SEMICONDUCTORS ]
