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WM2639

12-Bit Parallel Input Voltage Output DAC with Internal Reference

Wolfson Microelectronics plc 

WM2639

Production Data

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:

( ) CODE

Output voltage = 2 VREF

4096

INPUT

OUTPUT

1111

1111

1111

( ) 4095

2 VREF

4096

:

:

1000

0000

0001

( ) 2049

2 VREF

4096

1000

0000

0000

( ) 2048

2 VREF

= VREF

4096

0111

1111

1111

( ) 2047

2 VREF

4096

:

:

0000

0000

0001

( )1

2 VREF

4096

0000

0000

0000

0V

Table 1 Binary Code Table (0V to 2VREF Output), Gain = 2

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 2kΩ

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.

WOLFSON MICROELECTRONICS LTD

Production Data Rev 1.0 July 1999

8

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