1. Comparators with Hysteresis
E2E: TLV1702-Q1 hysteresis adjustment
Zak Kaye
Thomas Kuehl

2. The Comparator function
V1 and V2 are two input voltages applied to +IN and -IN inputs
Either one may be a dc level, or a changing ac signal
Vout can be one of two levels; VH − high (1), or VL − low (0)
VH ≈ V+ and VL ≈ 0 V, or GND
Non-inverting condition
If V1 > V2, Vout will be high
If V1 < V2, Vout will be low
Inverting condition
If V2 > V1, Vout will be low
If V2 < V1, Vout will be high
The comparator’s purpose is to compare two voltages, each one applied to one of its two inputs, and make an output state decision which is either high (1), or low (0). One input is an inverting input, while the other is a non-inverting input. It is the voltage level on one input, relative to the other, that is acted upon and results in the decision of a high, or low, output state.
The output state is determined by the two input levels:
Non-inverting setup
If V1 > V2, Vout will be high
If V1 < V2, Vout will be low
Inverting setup
If V2 > V1, Vout will be low
If V2 < V1, Vout will be high

3. Setting up a comparator circuit to use hysteresis Non-inverting comparator, open-collector
Goals
VHYST 100 mV, Vref 2.5 V
Let
Vcc = 5 V, VO(max) = 5 V, VO(min) = 50 mV
R1 = 100 K, Rpull-up = 10 k
Then
R2= R1 Vcc Vref − = −1 = 100 k
R3= R1∙R2 R1+R2 = ∙ = 50 k
R4=R3 𝑉 𝑂(𝑚𝑎𝑥) − 𝑉 𝑂(𝑚𝑖𝑛) V HYST −1 =5∙ − −1
R4=2.43 MEG
Equations simplified by setting
Rpull-up < 0.1*R4
Threshold voltage errors are in low percent range
A procedure is provided for determining the resistor values based on a specific hysteresis requirement. The procedure is specific to the non-inverting comparator having an open-drain, or open-collector output. The hysteresis voltage will be most accurate when Rpull-up << than R4; however, even with Rpull-up equal 1/10th to R4 it will be only off by a few percent.

4. Setting up a comparator circuit to use hysteresis TLV1701 Non-inverting comparator, open-collector, 100 mV HHYST
VH = 2.55 V
VL = 2.45 V
VHYST = 100 mV
TINA-TI simulation
and verification
Hysteresis accuracy improves with Rpull-up < 0.1 R4
Equations can be used for push-pull output too!
The calculated hysteresis procedure for the non-inverting, comparator output levels were tested using a TINA-TI simulation. The TLV1701 open-collector comparator was used for the simulation and the results are very good. With a reference level Vref of 2.5 V the upper and lower trip voltage levels are 2.55 V and 2.45 V respectively. The hysteresis voltage is very close to the desired 100 mV.

5. Setting up a comparator circuit to use hysteresis TLV1701 Inverting comparator, open-collector
Goals
VHYST = 50 mV, Vref = 2.5 V
Let
Vcc = 5 V, VO(max) = 5.0 V, VO(min) = 0.05 V
R1 = 10 k, Rpull-up = 10 k
Then
R2= 𝑅1 𝑉𝑐𝑐 𝑉𝑟𝑒𝑓 − = −1 = 10 k
R3= 𝑅1∙𝑅2 𝑅1+𝑅 𝑉 𝑂(𝑚𝑎𝑥) − 𝑉 𝑂(𝑚𝑖𝑛) V HYST −1
R3= ∙ − −1 = 490 k
The resistor equations for the establishing a specific level of hysteresis for the inverting comparator circuit are provided.

6. Setting up a comparator circuit to use hysteresis Inverting comparator, open-collector, 50 mV VHYST
VH = 2.52 V
VL = 2.47 V
VHYST = 49.5 mV
TINA-TI simulation
and verification
Hysteresis accuracy improves with Rpull-up < 0.1 R3
Equations can be used for push-pull output too!
The hysteresis is verified by TINA to be very close to the desired 50 mV.

7. Push-pull comparators with
Setting up a comparator circuit to use hysteresis Some guidelines when applying hysteresis
Push-pull comparators with
hysteresis applied
The resistor values directly affect the reference voltage and the VH and VL levels. Their tolerances are an important factor in hysteresis accuracy
Keeping Rpull-up ≤ 10 % of the feedback resistor value for open-drain/ collector outputs assures more accurate VH and VL voltage levels
The inverting and non-inverting equations can be used for push-pull output comparators
Use the datasheet Output Voltage vs Output Current curves to establish VO(max) and VO(min) from the VOH and VOL levels
The resistors used to set the comparator hysteresis are the primary contributors affecting the accuracy. That means that low tolerance resistors having a value near the computed value should be used for best accuracy.
Keeping the Rpull-up to a fraction the feedback resistor value will result in more accurate VH and VL voltage levels.
The hysteresis equations can be used for a push-pull output comparator too. Just as with the open-collector output the VO(max) and VO(min) levels will need to be estimated. This can be obtained from the Output Voltage vs. Output Current curves in the datasheet.