PCF8591 datasheet(11/28 Pages) PHILIPS

11 / 28 page

2003 Jan 27

Philips Semiconductors

Product speciﬁcation

8-bit A/D and D/A converter

PCF8591

7.5

Reference voltage

For the D/A and A/D conversion either a stable external

voltage reference or the supply voltage has to be applied

to the resistor divider chain (pins VREF and AGND).

The AGND pin has to be connected to the system analog

ground and may have a DC off-set with reference to VSS.

A low frequency may be applied to the VREF and AGND

pins. This allows the use of the D/A converter as a

one-quadrant multiplier; see Chapter 15 and Fig.7.

The A/D converter may 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 user has to keep the

reference voltage stable during the conversion cycle.

7.6

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 has to be connected to VSS. At the OSC pin the

oscillator frequency is available.

If the EXT pin is connected to VDD the oscillator output

OSC is switched to a high-impedance state allowing the

user to feed an external clock signal to OSC.

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