Production Data

WM2331

WOLFSON MICROELECTRONICS LTD

PD Rev 1.4 April 2001

11

MODE

PIN

MODE

FUNCTION

COMMENTS

AGND

Full external

REFTS

REFTF

=

REFBS

REFBF

=

On-chip reference generator and reference buffer are

not used.

AVDD/2

Differential

2

REF

V

AVDD

REFTF

+

=

2

REF

V

AVDD

REFTF

−

=

REFTS and REFBS are joined together and connected

either to the negative end of the input signal (true

differential mode) or to the AIN mid-scale voltage

(centre-span mode).

AVDD

Top/Bottom

()

2

REFBS

REFTS

AVDD

REFTF

−

+

=

()

2

REFBS

REFTS

AVDD

REFBF

−

−

=

On-chip reference generator is not used. Reference

buffer centers external reference voltages around

AVDD/2.

Table 1 WM2331 Reference Generation Modes

FULL EXTERNAL REFERENCE MODE (MODE = AGND)

When MODE is connected to AGND, the WM2331 operates in full external reference mode. The

internal reference buffer is powered down and bypassed, so that the ADC core takes the user-

supplied reference voltages at pins REFTS and REFBS (REFTS and REFBS are internally

connected to REFTF and REFBF). The mean of REFTF and REFBF must be equal to AVDD/2. Only

single-ended input is possible in this mode.

SAMPLE

AND

HOLD

REFTS

REFBS

AIN

-1/2

+1

-1/2

PGA

REFTF

REFBF

INTERNAL

REFERENCE

BUFFER

ADC

CORE

Figure 7 ADC Reference Generation in Full External Mode

The full external mode of operation is useful when the application requires more accurate or lower

drift reference voltages than the WM2331 can provide, or when devices need to share common

reference voltages for best ADC matching. It also offers the possibility of using REFTS and REFBS

as sense lines to drive the REFTF and REFBF lines (Kelvin mode) to eliminate any voltage drops

from remote references within the system (see Figure 9). In Kelvin configurations, take care when

choosing the external op-amps to ensure that they can drive large capacitive loads without

oscillating.

Although the on-chip reference generator is not used by the WM2331 in full external mode, its output

is available on the VREF pin and can be used by other parts of the system. Note that in addition to

the internal connections from REFTS to REFTF and REFBS to REFBF, external wire connections

must also be made as shown in Figure 8 to minimise resistance (except in Kelvin mode).