User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 730
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30.3.2.4 Non-inverting PGA
Figure 30.5 (p. 730) shows the non-inverting input configuration. In this mode the negative input is
connected to the resistor ladder by setting the OPAxNEGSEL bitfield to OPATAP in DACn_OPAxMUX.
This setting provides a programmable gain on the negative input, which can be set by choosing
the wanted gain value in the RESSEL bitfield in DACn_OPAxMUX. In addition the OPAxRESINMUX
bitfield must be set to VSS or NEGPAD in DACn_OPAxMUX. The positive input is selected by
the OPAxPOSSEL bitfield, and the output is configured by the OUTPEN bitfield, both located in
DACn_OPAxMUX.
Figure 30.5. Non-inverting PGA Overview
R1
R2
VIN
-
+
VOUT
VOUT= VIN(1+ R2/R1)
Table 30.4. Non-inverting PGA Configuration
OPA bitfields OPA Configuration
OPAx POSSEL NEXTOUT, POSPADx, DACx
OPAx NEGSEL OPATAP
OPAx RESINMUX VSS, NEGPAD
30.3.2.5 Cascaded Inverting PGA
This mode enables the opamp signals to be internally configured to cascade two or three opamps in
inverting mode as shown in Figure 30.6 (p. 730) . In both cases the positive input will be configured
to signal ground by setting OPAxPOSSEL bitfield to PAD in DACn_OPAx_MUX. When cascaded, the
negative input is connected to the resistor ladder by setting the OPAxNEGSEL bitfield to OPATAP in
DACn_OPAxMUX. The input to the resistor ladder can be configured in the OPAxRESINMUX bitfield
in DAC_nOPAxMUX. The output from OPA0 can be connected to OPA1 to create the second stage
by setting the NEXTOUT bitfield in DACn_OPAxMUX. To complete the stage, OPA1RESINMUX field
must be set to OPA0INP. Similarly, the last stage can be created by setting the NEXTOUT bitfield in
DACn_OPA1MUX and OPA2RESINMUX bitfield to OPA1INP in DACn_OPA2MUX.
Figure 30.6. Cascaded Inverting PGA Overview
R1
R2
VIN
-
+
POS0
VOUT1= -(VIN-POS0) x R2/R1 + POS0
VOUT2= -(VOUT1-POS1) x R2/R1 + POS1
VOUT3= -(VOUT2-POS3) x R2/R1 + POS3
R1
R2
-
+
POS1
R1
R2
-
+
POS2
Table 30.5. Cascaded Inverting PGA Configuration
OPA OPA bitfields OPA Configuration
OPA0 POSSEL POSPAD0