WM2637

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 1.0 July 99

8

PROGRAMMABLE SETTLING TIME

Settling time is a software selectable 1

µs or 3.5µs typical, to within ±0.5LSB of final value. This is

controlled by the value of D14. A ONE defines a settling time of 1

µs, a ZERO defines a settling time

of 3.5

µs.

PROGRAMMABLE POWER DOWN

The power down function is controlled by D13. A ZERO configures the device as active, or fully

powered up, a ONE configures the device into power down mode. When the power down function is

released the device reverts back to the DAC code set prior to power down.

REGISTER ADDRESSING

A separate internal control register is available. This is accessed from the register access bits R1

(Bit D15) and R0 (Bit D12).

R1

(BIT D15)

R0

(BIT D12)

REGISTER

0

0

Write data to DAC B and BUFFER

0

1

Write data to BUFFER

1

0

Write data to DAC A and update DAC B with BUFFER content

1

1

Write data to control register

Table 3 Programmable Options

The contents of the control register, shown below in Table 4, are used to program the internal

reference function

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

x

x

x

x

x

x

x

x

x

X

REF1 REF0

Table 4 Control Register Contents

PROGRAMMABLE INTERNAL REFERENCE

The reference can be sourced internally or externally under software control. If an external reference

voltage is applied to the REF pin, the device must be configured to accept this.

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 10M

Ω and an input

capacitance of typically 55pF. The reference voltage determines the DAC full-scale output.

If an internal reference is selected, a voltage of 1.024V or 2.048V is available. The internal

reference can source up to 1mA and can therefore be used as an external system reference.

REF1

(BIT D1)

REF0

(BIT D0)

REGISTER

0

0

External

0

1

1.024V

1

0

2.048V

1

1

External

Table 5 Internal Reference Options

Examples:

1.

Set internal reference voltage to 2.048V

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

1

x

0

1

x

x

x

x

x

x

x

x

x

x

1

0

2.

Write new DAC A value and update DAC A output

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

0

x

0

0

New DAC A output value

x

x