Detailed Description
The MAX9092/MAX9093/MAX9094/MAX9095 are low-
cost, general-purpose comparators that have a single-
supply +1.8V to +5V operating voltage range. The
common-mode input range extends from -0.1V below the
negative supply to within +0.8V of the positive supply.
They require approximately 65µA per comparator with a
5V supply and 50µA with a 2.7V supply.
The MAX9093/MAX9095 have 2mV of hysteresis for
noise immunity. This significantly reduces the chance of
output oscillations even with slow-moving input signals.
Applications Information
Hysteresis
Many comparators oscillate in the linear region of opera-
tion because of noise or undesired parasitic feedback.
This tends to occur when the voltage on one input is
equal or very close to the voltage on the other input. The
MAX9093/MAX9095 have internal hysteresis to counter
parasitic effects and noise.
The hysteresis in a comparator creates two trip points:
one for the rising input voltage and one for the falling input
voltage (Figure 1). The difference between the trip points
is the hysteresis. When the comparator’s input voltages
are equal, the hysteresis effectively causes one com-
parator input to move quickly past the other, thus taking
the input out of the region where oscillation occurs. This
provides clean output transitions for noisy, slow-moving
input signals.
Additional hysteresis can be generated with two resistors
using positive feedback (Figure 2). Use the following pro-
cedure to calculate resistor values:
1) Find output voltage when output is high:
VOUT(HIGH) = VDD - ILOAD x RL
2) Find the trip points of the comparator using these for-
mulas:
VTH = VREF + ((VOUT(HIGH) - VREF)R2)/(R1 + R2)
VTL = VREF(1 - (R2/(R1 + R2)))
where VTH is the threshold voltage at which the compara-
tor switches its output from high to low as VIN rises above
the trip point, and VTL is the threshold voltage at which
the comparator switches its output from low to high as VIN
drops below the trip point.
3) The hysteresis band is:
VHYST = VTH - VTL = VDD(R2/(R1 + R2))
In this example, let VDD = 5V, VREF = 2.5V, ILOAD =
50nA, and RL = 5.1kΩ.
VOUT(HIGH) = 5.0V - (50 x 10-9 x 5.1 x 103Ω) ≈ 5.0V
VTH = 2.5 + 2.5(R2/(R1 + R2))
VTL = 2.5(1 - (R2/(R1 + R2)))
Select R2. In this example, choose 1kΩ.
Select VHYST. In this example, choose 50mV.
Solve for R1.
VHYST = VOUT(HIGH)(R2/(R1 + R2))V
0.050V = 5(1000/(R1 + 1000))V
where R1 ≈ 100kΩ, VTH = 2.525V, and VTL = 2.475V
Choose R1 and R2 to be large enough as not to exceed
the amount of current the reference can supply.
The source current required is VREF/(R1 + R2).
The sink current is (VOUT(HIGH) - VREF) x (R1 + R2).
Figure 1. Threshold Hysteresis Band (Not to Scale) Figure 2. Adding Hysteresis with External Resistors
IN+ THRESHOLDS
IN-
VHYST VTL
VTH
HYSTERESIS
BAND
OUT
IN+
OUT
RL
R1
R2
VREF
VIN
VDD
VOUT
VDD
VSS
IN-
MAX9093/MAX9095
MAX9092/MAX9093/
MAX9094/MAX9095
General-Purpose, Low-Voltage,
Dual/Quad, Tiny Pack Comparators
www.maximintegrated.com Maxim Integrated
│
9