WM2618

Production Data

WOLFSON MICROELECTRONICS LTD

6

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 registers 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.

EXTERNAL REFERENCE

The reference voltage input is buffered which makes the DAC input resistance independent

of code. The REFIN input resistance is 10M

Ω and the REFIN input capacitance is typically

5pF. The reference voltage determines the DAC full-scale output.

SERIAL INTERFACE

When chip select (NCS) is low, the input data is read into a 16-bit shift register with the input

data clocked in most significant bit first. The falling edge of the SCLK input shifts the data

into the input register. After 16 bits have been transferred, the next rising edge on SCLK or

NCS then transfers the data to the DAC latch. When NCS is high, input data cannot be

clocked into the input register (see Table 2).

SERIAL CLOCK AND UPDATE RATE

Figure 1 shows the device timing. The maximum serial rate is:

MHz

20

t

t

1

min

WCL

min

WCH

=

+

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.