WM8200

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PP Rev 1.22 March 2002

13

REFERENCE VOLTAGE GENERATION

The WM8200 incorporates an on-chip 0.5V bandgap voltage reference that can be used to derive a

temperature and supply independent voltage on pin VREF. The VREF output can be used for driving

external loads or setting the ADC input range. The voltage is programmed via connections made to

the REFSENSE pin as shown in Table 4.

REFSENSE

VREF output

Refer to

AGND

1.0V

Figure 7

AVDD

Hi impedance – A1 amplifier disabled

If using the ADC reference generator then an

external VREF source must be applied to the

VREF pin.

Figure 8

Connect to VREF

0.5V

Figure 9

R network to VREF / AGND

Between 0.5 V and 1 V

VREF=0.5x(1+Ra/Rb)

Figure 10

Table 4: – VREF output control by REFSENSE connection

+

A1

-

+

0.5V

-

VREF

REFSENSE

AVSS

10k

10k

Figure 7: VREF=1V

+

A1

-

+

0.5V

-

VREF

REFSENSE = AVDD

AVSS

Figure 8: VREF=Hi Impedance

+

A1

-

+

0.5V

-

VREF

REFSENSE

AVSS

Figure 9: VREF=0.5V

+

A1

-

+

0.5V

-

VREF

REFSENSE

AVSS

Ra

Rb

Figure 10: VREF between 0.5 and 1V

When enabled, the on-chip voltage reference should be externally decoupled (see Reference

Decoupling Section for details).

In internal ADC references mode (MODE=AVDD), the voltages at REFT and REFB are:

REFT =

(AVDD + VREF) / 2

REFB =

(AVDD – VREF) / 2

If external ADC references mode (MODE=AVSS), the average value of the external voltages applied

to REFT and REFB should be AVDD/2 for correct device operation.