Download Comparator with Hysteresis

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
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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
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