WM2130

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 1.2 April 2001

10

FULL EXTERNAL REFERENCE MODE (MODE = AGND)

When MODE is connected to AGND, the WM2130 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.

REFTS

REFBS

AIN

REFTF

REFBF

ADC

CORE

SAMPLE

AND

HOLD

-1/2

+1

-1/2

INTERNAL

REFERENCE

BUFFER

Figure 6 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 WM2130 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 7). 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 WM2130 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).

AVDD/2

AVDD

AIN

MODE

REFSENSE

DC SOURCE =

AVDD/2 + [(+FS) - (-FS)] * GAIN/2

DC SOURCE =

AVDD/2 - [(+FS) - (-FS)] * GAIN/2

REFTF

REFBF

+FS

-FS

REFTS

REFBS

0.1µF

10µF

0.1µF

0.1µF

Figure 7 Full External Reference Mode (Reference Generator Disabled)