WM2636
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
1111
(
VREF
)
4096
INPUT
OUTPUT
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.
SERIAL INTERFACE
Explanation of data transfer:
First, the device has to be enabled with NCS set to low. Then, a falling edge of FS starts
shifting the data bit-per-bit (starting with the MSB) to the internal register on the falling edges of
SCLK. After 16 bits have been transferred or FS rises, the content of the shift register is 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 chip select (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, then NCS can be tied low.
SERIAL CLOCK AND UPDATE RATE
Figure 1 shows the device timing. The maximum serial rate is:
1
fSCLKmax =
= 20MHz
tWCH min+ tWCL min
The digital update rate is limited to an 800ns period, or 1.25MHz frequency. However, the DAC
settling time to 12 bits limits the update rate for large input step transitions.
WOLFSON MICROELECTRONICS LTD
PD Rev 1.0 July 1999
7
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
