WM8200
Product Preview
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
AGND
VREF output
Refer to
Figure 7
Figure 8
1.0V
AVDD
Hi impedance – A1 amplifier disabled
If using the ADC reference generator then an
external VREF source must be applied to the
VREF pin.
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
-
+
-
VREF
+
0.5V
-
+
0.5V
-
VREF
A1
10k
10k
REFSENSE
REFSENSE
AVSS
AVSS
Figure 7: VREF=1V
Figure 9: VREF=0.5V
+
A1
-
+
A1
-
VREF
+
0.5V
-
+
0.5V
-
VREF
Ra
REFSENSE
Rb
REFSENSE = AVDD
AVSS
AVSS
Figure 10: VREF between 0.5 and 1V
Figure 8: VREF=Hi Impedance
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.
PP Rev 1.22 March 2002
13
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
