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Comparators with Hysteresis E2E: TLV1702-Q1 hysteresis adjustment Zak Kaye Thomas Kuehl 1 The Comparator function • V1 and V2 are two input voltages applied to +IN and -IN inputs V+ -IN Vout V2 +IN V1 • 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 2 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, R1 = 100 K, VO(max) = 5 V, VO(min) = 50 mV Rpull-up = 10 k Then R2 = R3 = • Equations simplified by setting Rpull-up < 0.1*R4 • Threshold voltage errors are in low percent range R1 Vcc −1 Vref = 104 = 100 k 5.0 −1 2.5 105 ∙105 R1∙R2 = = 50 k R1+R2 105 +105 R4 = R3 𝑉𝑂(𝑚𝑎𝑥) − 𝑉𝑂(𝑚𝑖𝑛) −1 VHYST = 5 ∙ 104 5.0 −0.05 0.10 −1 R4 = 2.43 MEG 3 Setting up a comparator circuit to use hysteresis TLV1701 Non-inverting comparator, open-collector, 100 mV HHYST TINA-TI simulation and verification • Hysteresis accuracy improves with Rpull-up < 0.1 R4 • Equations can be used for push-pull output too! VH = 2.55 V VL = 2.45 V VHYST = 100 mV 4 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, R1 = 10 k, Rpull-up = 10 k VO(min) = 0.05 V Then 104 = 10 k 5.0 −1 2.5 R2 = 𝑅1 𝑉𝑐𝑐 −1 𝑉𝑟𝑒𝑓 = R3 = 𝑅1∙𝑅2 𝑅1+𝑅2 𝑉𝑂(𝑚𝑎𝑥) − 𝑉𝑂(𝑚𝑖𝑛) −1 VHYST R3 = 104 ∙104 104 +104 5.0−0.05 0.05 −1 = 490 k 5 Setting up a comparator circuit to use hysteresis Inverting comparator, open-collector, 50 mV VHYST TINA-TI simulation and verification • Hysteresis accuracy improves with Rpull-up < 0.1 R3 • Equations can be used for push-pull output too! VH = 2.52 V VL = 2.47 V VHYST = 49.5 mV 6 Setting up a comparator circuit to use hysteresis Some guidelines when applying hysteresis • The resistor values directly affect the reference voltage and the VH and VL levels. Their tolerances are an important factor in hysteresis accuracy Push-pull comparators with hysteresis applied • 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 7