PCF8591
NXP Semiconductors
8-bit A/D and D/A converter
HEX
CODE
7F
7E
02
01
00
−128 −127
−2
−1
0
1
2
126
127
V
AIN +
− V
AIN −
FF
V
lsb
FE
V
REF
− V
AGND
V
=
lsb
256
81
80
mbl831
Fig 10. A/D conversion characteristics of differential inputs
8.5 Reference voltage
For the D/A and A/D conversion, either a stable external voltage reference or the supply
voltage must be applied to the resistor divider chain (pins VREF and AGND). The AGND
pin has to be connected to the system analog ground. It may have a DC off-set with
reference to VSS
.
A low frequency can be applied to the VREF and AGND pins. This allows the use of the
D/A converter as a one-quadrant multiplier (see Section 10 and Figure 6)
The A/D converter can also be used as a one or two quadrant analog divider. The analog
input voltage is divided by the reference voltage. The result is converted to a binary code.
In this application, the reference voltage must be kept stable during the conversion cycle.
8.6 Oscillator
An on-chip oscillator generates the clock signal required for the A/D conversion cycle and
for refreshing the auto-zeroed buffer amplifier. When using this oscillator the EXT pin must
be connected to VSS. The oscillator frequency is available at the OSC pin.
If the EXT pin is connected to VDD, the oscillator output OSC is switched to a
high-impedance state allowing to feed an external clock signal to OSC.
PCF8591
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2013. All rights reserved.
Product data sheet
Rev. 7 — 27 June 2013
10 of 31
NXP [ NXP ]
