pcf8591 NXP Semiconductors, pcf8591 Datasheet - Page 7

• Manufacturer Part Number: pcf8591
• Description: 8-bit A/d And D/a Converter
• Manufacturer: NXP Semiconductors

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