35.3.7 Application Usage

The OPAMP peripheral is highly flexible and can be used in various analog signal conditioning applications. This section describes a broad range of configurations and the multiplexer settings required to achieve them. Many of these configurations require no external components.

Figure 35-2. Op Amp Connected Directly to Pins
The figure above displays an op amp connected directly to the pins of the device without being connected to any of the internal resistors. This is useful for situations where the user desires to make all connections to other components externally. The multiplexer settings required to achieve this configuration are:
Table 35-3. Op Amp Connected Directly to Pins
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OPn INP INN OFF WIP0 OFF

Figure 35-3. Voltage Follower
The figure above displays a voltage follower, also known as a unity-gain buffer. The non-inverting (+) input is connected to a pin, and the output is connected to the inverting (-) input. The multiplexer settings required for this configuration are:
Table 35-4. Voltage Follower
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OPn INP OUT OFF WIP0 OFF

Figure 35-4. Non-Inverting PGA
The figure above displays a non-inverting Programmable Gain Amplifier. The required multiplexer settings are as follows:
Table 35-5. Non-Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OPn INP WIP GND Setting determines gain OUT

Figure 35-5. Inverting PGA
The figure above shows the inverting PGA configuration. The multiplexer settings required are:
Table 35-6. Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OPn VDDDIV2 WIP INN Setting determines gain OUT

Figure 35-6. Integrator
The figure above shows how an op amp can be configured as an integrator. An external capacitor and external resistor are required. The DUMPn event closes a switch to discharge the capacitor and reset the integrator. The multiplexer settings required are:
Table 35-7. Integrator
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OPn VDDDIV2 INN OFF WIP0 OFF

Figure 35-7. Differential Amplifier using Two Op Amps
The figure above shows how a differential amplifier can be constructed from two op amps. The differential amplifier accepts two input signals, V1 and V2. The output also consists of two signals, OP1OUT and V2. The difference of the output signals, VDIFF, is proportional to the difference (V2-V1) of the two input signals. The multiplexer settings required to implement this configuration are as follows:
Table 35-8. Differential Amplifier using Two Op Amps
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 INP OUT OFF WIP0 OFF
OP1 INP WIP LINKOUT (OP0OUT) Setting determines gain OUT

Figure 35-8. Cascaded (Two) Non-Inverting PGA
The figure above shows a cascaded non-inverting PGA constructed from two op amps. The following multiplexer settings are required:
Table 35-9. Cascaded (Two) Non-Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 INP WIP GND Determines gain OUT
OP1 LINKOUT (OP0OUT) WIP GND Determines gain OUT

Figure 35-9. Cascaded (Two) Inverting PGA
The figure above shows a cascaded inverting PGA constructed from two op amps. The required multiplexer settings are:
Table 35-10. Cascaded (Two) Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 VDDDIV2 WIP INN Determines gain OUT
OP1 VDDDIV2 WIP LINKOUT (OP0OUT) Determines gain OUT

Figure 35-10. Cascaded (Three) Non-Inverting PGA
The figure above shows a cascaded non-inverting PGA constructed from three op amps. The following multiplexer settings are required:
Table 35-11. Cascaded (Three) Non-Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 INP WIP GND Determines gain OUT
OP1 LINKOUT (OP0OUT) WIP GND Determines gain OUT
OP2 LINKOUT (OP1OUT) WIP GND Determines gain OUT

Figure 35-11. Cascaded (Three) Inverting PGA
The figure above shows a cascaded inverting PGA constructed from three op amps. The required multiplexer settings are:
Table 35-12. Cascaded (Three) Inverting PGA
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 VDDDIV2 WIP INN Determines gain OUT
OP1 VDDDIV2 WIP LINKOUT (OP0OUT) Determines gain OUT
OP2 VDDDIV2 WIP LINKOUT (OP1OUT) Determines gain OUT

Figure 35-12. Instrumentation Amplifier
The figure above displays three op amps configured as an instrumentation amplifier. The following multiplexer settings are required:
Table 35-13. Instrumentation Amplifier
OPnINMUX OPnRESMUX
MUXPOS MUXNEG MUXBOT MUXWIP MUXTOP
OP0 INP OUT GND See the table below OUT
OP1 INP OUT OFF WIP0 OFF
OP2 LINKWIP (OP0WIP) WIP LINKOUT (OP1OUT) See the table below OUT
Configure the resistor ladders associated with OP0 and OP2 as follows to select the desired gain:
Table 35-14. Gain Selection for Instrumentation Amplifier
GAIN OP0RESMUX.MUXWIP OP2RESMUX.MUXWIP
1/15 0x7 0x0
1/7 0x6 0x1
1/3 0x5 0x2
1 0x3 0x3
3 0x2 0x5
7 0x1 0x6
15 0x0 0x7