TMS32020 datasheet(39/57 Pages) TI

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4–1

4 Parameter Measurement Information

Rfb = 4R for D6 = 0, and D7 = 1

Rfb = 2R for D6 = 1 and D7 = 0

D6 = 0 and D7 = 0

Rfb = R for D6 = 1 and D7 = 1

To Multiplexer

Rfb

–

IN –

AUX IN –

IN +

AUX IN +

–

Rfb

Figure 4–1. IN + and IN – Gain Control Circuitry

Table 4–1. Gain Control Table (Analog Input Signal Required for

Full-Scale Bipolar A/D Conversion Twos Complement)†

INPUT

CONTROL REGISTER BITS

ANALOG

A/D CONVERSION

CONFIGURATIONS

ANALOG

INPUT‡§

RESULT

VID = ± 6V

±full scale

Differential configuration

VID = ± 6 V

±full scale

Analog input = IN + – IN –

= AUX IN + – AUX IN –

VID = ± 3 V

±full scale

= AUX IN + – AUX IN –

VID = ± 1.5 V

±full scale

VI = ± 3V

±half scale

Single-ended configuration

Analog input

IN +

ANLG GND

VI = ± 3 V

±half scale

Analog input = IN + – ANLG GND

= AUX IN + –ANLG GND

VI = ± 3 V

±full scale

= AUX IN + ANLG GND

VI = ± 1.5 V

±full scale

† VCC+ = 5 V, VCC– = –5 V, VDD = 5 V

‡ VID = Differential Input Voltage, VI = Input voltage referenced to ground with IN– or AUX IN– connected to GND.

§ In this example, Vref is assumed to be 3 V. In order to minimize distortion, it is recommended that the analog input not

exceed 0.1 dB below full scale.

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