WM2331CDT/V Просмотр технического описания (PDF) - Wolfson Microelectronics plc

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WM2331CDT/V

10-bit 30MSPS ADC with PGA and Clamp

Wolfson Microelectronics plc 

Production Data

WM2331

MODE

PIN

AGND

AVDD/2

AVDD

MODE

Full external

Differential

Top/Bottom

FUNCTION

COMMENTS

REFTF = REFTS

REFBF = REFBS

REFTF = AVDD + VREF

2

REFTF = AVDD − VREF

2

REFTF = AVDD + (REFTS − REFBS )

2

REFBF = AVDD − (REFTS − REFBS )

2

On-chip reference generator and reference buffer are

not used.

VREF can be internally or externally generated.

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).

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.

REFTF

AIN

REFTS

REFBS

+1

SAMPLE

-1/2 AND

HOLD

-1/2

PGA

INTERNAL

REFERENCE

BUFFER

ADC

CORE

REFBF

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).

WOLFSON MICROELECTRONICS LTD

PD Rev 1.4 April 2001

11

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