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 1. 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 1. Op Amp Connected Directly to Pins
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OPn	INP	INN	OFF	WIP0	OFF

Figure 2. 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 2. Voltage Follower
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OPn	INP	OUT	OFF	WIP0	OFF

Figure 3. Non-Inverting PGA

The figure above displays a non-inverting Programmable Gain Amplifier. The required multiplexer settings are as follows:

Table 3. Non-Inverting PGA
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OPn	INP	WIP	GND	Setting determines gain	OUT

Figure 4. Inverting PGA

The figure above shows the inverting PGA configuration. The multiplexer settings required are:

Table 4. Inverting PGA
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OPn	VDDDIV2	WIP	INN	Setting determines gain	OUT

Figure 5. 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 5. Integrator
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OPn	VDDDIV2	INN	OFF	WIP0	OFF

Figure 6. 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, V_DIFF, is proportional to the difference (V2-V1) of the two input signals. The multiplexer settings required to implement this configuration are as follows:

Table 6. Differential Amplifier using Two Op Amps
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OP0	INP	OUT	OFF	WIP0	OFF
OP1	INP	WIP	LINKOUT (OP0OUT)	Setting determines gain	OUT

Figure 7. 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 7. Cascaded (Two) Non-Inverting PGA
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OP0	INP	WIP	GND	Determines gain	OUT
OP1	LINKOUT (OP0OUT)	WIP	GND	Determines gain	OUT

Figure 8. Cascaded (Two) Inverting PGA

The figure above shows a cascaded inverting PGA constructed from two op amps. The required multiplexer settings are:

Table 8. Cascaded (Two) Inverting PGA
	MUXPOS	MUXNEG	MUXBOT	MUXWIP	MUXTOP
OP0	VDDDIV2	WIP	INN	Determines gain	OUT
OP1	VDDDIV2	WIP	LINKOUT (OP0OUT)	Determines gain	OUT

Figure 9. 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 9. Cascaded (Three) Non-Inverting PGA
	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 10. Cascaded (Three) Inverting PGA

The figure above shows a cascaded inverting PGA constructed from three op amps. The required multiplexer settings are:

Table 10. Cascaded (Three) Inverting PGA
	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 11. Instrumentation Amplifier

The figure above displays three op amps configured as an instrumentation amplifier. The following multiplexer settings are required:

Table 11. Instrumentation Amplifier
	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

The resistor ladders associated with OP0 and OP2 must be configured as follows to select the desired gain:

Table 12. 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`