Production Data

WM2623

WOLFSON MICROELECTRONICS LTD

PD Rev 1.0 October 2000

7

DEVICE DESCRIPTION

GENERAL FUNCTION

The WM2623 is an 8-bit, voltage output DAC operating from a single supply. The device uses a

resistor string network buffered with an op amp to convert 8-bit digital data to analogue voltage

levels (see Block Diagram). The output voltage is determined by the reference input voltage and

the input code according to the following relationship:

()

256

2

CODE

V

out

V

REFIN

=

INPUT

OUTPUT

1111

1111

()

256

255

2

REF

V

::

1000

0001

()

256

129

2

REF

V

1000

0000

()

REF

REF

V

V

=

256

128

2

0111

1111

()

256

127

2

REF

V

::

0000

0001

()

256

1

2

REF

V

0000

0000

0V

POWER ON RESET

An internal power-on-reset circuit resets the DAC register to all 0s on power-up.

BUFFER AMPLIFIER

The output buffer has a near rail-to-rail output with short circuit protection and can reliably drive a

2k

Ω load with a 100pF load capacitance.

EXTERNAL REFERENCE

The reference voltage input is buffered which makes the DAC input resistance independent of

code. The REF pin has an input resistance of 10M

Ω and an input capacitance of typically 5pF. The

reference voltage determines the DAC full-scale output.

SERIAL INTERFACE

Before writing any data to the WM2623, the device must first be enabled by setting CSB to low.

Then, a falling edge of FS starts shifting the data bit-per-bit (starting with the MSB) into the internal

register on the falling edges of SCLK. After 16 bits have been transferred, the next rising edge on

SCLK or FS causes the content of the shift register to be moved to the DAC latch which updates

the voltage output to the new level.

The serial interface of the device can be used in two basic modes:

•

four wire (with chip select)

•

three wire (without chip select)

Using the chip select pin CSB (four wire mode), it is possible to have more than one device

connected to the serial port of the data source (DSP or microcontroller). If there is no need to have

more than one device on the serial bus, CSB can be tied low.