WM2639

Production Data

WOLFSON MICROELECTRONICS LTD

Production Data Rev 1.0 July 1999

8

DEVICE DESCRIPTION

GENERAL FUNCTION

The device uses a resistor string network buffered with an op amp to convert 12-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:

Output voltage =

( )

4096

CODE

V

2

REF

INPUT

OUTPUT

1111

1111

1111

( )

4096

4095

V

2

REF

:

:

1000

0000

0001

( )

4096

2049

V

2

REF

1000

0000

0000

( )

REF

REF

V

4096

2048

V

2

=

0111

1111

1111

( )

4096

2047

V

2

REF

:

:

0000

0000

0001

( )

4096

1

V

2

REF

0000

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.

HARDWARE CONFIGURATION OPTIONS

The WM2639 has one configuration option that is controlled by a device pin.

DAC UPDATE

The NLDAC pin (Pin 16) can be held high to prevent word writes from updating the DAC latch. By writing

the new value to the DAC then pulling NLDAC low, the new DAC code is loaded into the DAC latch.

PARALLEL INTERFACE

The device registers data on the positive edge of NWE (Pin 17). It must be enabled with NCS (Pin 18)

low. Whether the data is written to the DAC holding latch or the control register, depends on the state of

input pin REG (Pin 15). REG = 0 selects the DAC holding latch, REG = 1 selects the control register.