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
4096
2
2
(
(
VREF
)
)
:
:
1000
1000
0111
0000
0001
0000
1111
2049
4096
VREF
0000
1111
2048
4096
2
(
VREF
)
= VREF
2047
2
2
(
(
VREF
)
)
4096
:
:
0000
0000
0000
0001
0000
1
VREF
4096
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 2kW
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
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
