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2016-04-28 - Giant Gecko Family - d0053_Rev1.20
739
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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 30.7 (p. 739) . In both cases the positive input will be configured
to signal ground by setting OPAxPOSSEL bit-field to PAD in DACn_OPAx_MUX. When cascaded, the
negative input is connected to the resistor ladder by setting the OPAxNEGSEL bit-field to OPATAP in
DACn_OPAxMUX. The input to the resistor ladder can be configured in the OPAxRESINMUX bit-field
in DAC_nOPAxMUX. The output from OPA0 can be connected to OPA1 to create the second stage
by setting the NEXTOUT bit-field 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 bit-field in
DACn_OPA1MUX and OPA2RESINMUX bit-field to OPA1INP in DACn_OPA2MUX.
Figure 30.7. 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 bit-fields
OPA Configuration
OPA0
POSSEL
POSPAD0
OPA0
NEGSEL
OPA0TAP
OPA0
RESINMUX
NEGPAD0
OPA0
NEXTOUT
1
OPA1
POSSEL
POSPAD1
OPA1
NEGSEL
OPATAP
OPA1
RESINMUX
OPA0INP
OPA1
NEXTOUT
1
OPA2
POSSEL
POSPAD2
OPA2
NEGSEL
OPATAP
OPA2
RESINMUX
OPA1INP
30.3.2.6 Cascaded Non-inverting PGA
This mode enables the opamp signals to be internally configured to cascade two or three opamps in non-
inverting mode as shown in Figure 30.8 (p. 740) . In both cases the negative input for all opamps will be
connected to the resistor ladder by setting the OPAxNEGSEL bit-field to OPATAP. In addition the resistor
ladder input must be set to VSS or NEGPADx in the OPAxRESINMUX in DACn_OPAxMUX. When
cascaded, the positive input on OPA0 is configured by the OPA0POSSEL bit-field. The output from OPA0
can be connected to OPA1 to create the second stage by setting NEXTOUT in DACn_OPA0MUX. To
complete the stage, the OPA1POSSEL bit-field must be set to OPA0INP in DACn_OPA1MUX. Similarly,
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