Programmable Hysteresis

OPAMP can be configured as an inverting or non-inverting comparator with programmable hysteresis. Applying hysteresis will prevent constant toggling of the output, caused by noise when the input signals are close to each other.

In both inverting and non-inverting comparator configurations the positive input is connected to the resistor ladder. When OPAMP is configured as an inverting comparator with programmable hysteresis, the input voltage must be applied to the negative input and RES1MUX must be connected to the ground. When an OPAMP is configured as a non-inverting comparator with programmable hysteresis, the input voltage must be applied to RES1MUX and the negative input must be connected to the ground.

To configure an OPAMP as an inverting comparator with programmable hysteresis, the OPAMPCTRLx register can be configured as follows:

Table 1. Configuration of Input Multiplexes for OPAMP0 (Example: Vth = 3/4*Vcc, Ref = GND)
	MUXPOS	MUXNEG	RES1MUX	POTMUX	RES2VCC	RES2OUT	RES1EN	ANAOUT
OPAMP0	0001	000	010	001	0	1	1	0

Table 2. POTMUX [2:0]: Potentiometer Selection
Value	R1	R2	Threshold = Vcc * R1 / (R1 + R2)
0x0	14R	2R	7/8 * Vcc
0x1	12R	4R	3/4 * Vcc
0x2	8R	8R	1/2 * Vcc
0x3	6R	10R	3/8 * Vcc
0x4	4R	12R	1/4 * Vcc
0x5	3R	13R	3/16 * Vcc
0x6	2R	14R	1/8 * Vcc
0x7	R	15R	1/16 * Vcc

Figure 1. Inverting comparator with programmable hysteresis

To configure an OPAMP as a non-inverting comparator with programmable hysteresis, the OPAMPCTRLx register can be configured as follows:

Table 3. Configuration of Input Multiplexes for OPAMP0 and OPAMP1 (Example: Vth = 1/3*Vcc, Ref = Gnd)
	MUXPOS	MUXNEG	POTMUX	RES2OUT	RES1EN
OPAMP0	0001	010	100	1	1
OPAMP1	0001	010	100	1	1
OPAMP2	0001	010	100	1	1

Table 4. POTMUX [2:0]: Potentiometer Selection
Value	R1	R2	Threshold = Vcc * R1 / R2
0x0	14R	2R	Vcc * 7 (unused)
0x1	12R	4R	Vcc * 3 (unused)
0x2	8R	8R	Vcc (unused)
0x3	6R	10R	0.6* Vcc
0x4	4R	12R	1/3 * Vcc
0x5	3R	13R	3/13 *Vcc
0x6	2R	14R	1/7 * Vcc
0x7	R	15R	1/15 * Vcc

Figure 2. Non-Inverting comparator with programmable hysteresis