WM2633
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
(
VREF
)
)
:
:
1000
1000
0111
0000
0001
0000
1111
2049
4096
(
2 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
2kΩ load with a 100pF load capacitance.
EXTERNAL REFERENCE
If an external reference is selected, the reference voltage input is buffered which makes the DAC
input resistance independent of code. The REF pin has an input resistance of 10MΩ and an input
capacitance of typically 55pF. The reference voltage determines the DAC full-scale output.
HARDWARE CONFIGURATION OPTIONS
The device has three configuration options that are controlled by device pins.
DEVICE POWER DOWN
The device can be powered-down by pulling pin NPD (pin 15) high. This powers down the DAC. This
will reduce power consumption significantly. The NPD pin low overrides the software control bit
PWR. When the power down function is released the device reverts to the DAC code set prior to
power down.
SETTLING TIME
The settling time of the device can be controlled by pin SPD (pin 9). A ONE on pin SPD will ensure a
FAST settling time; a ZERO will ensure a SLOW settling time. The SPD pin high overrides the
software control bit SPD.
SIMULTANEOUS 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.
WOLFSON MICROELECTRONICS LTD
PD Rev 1.0 July 1999
8
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
