Rainbow Electronics LMX339 - Manual (Page 7)

LMX331/LMX393/LMX339
General-Purpose, Low-Voltage,
Single/Dual/Quad, Tiny-Pack Comparators
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Detailed Description
The LMX331/LMX393/LMX339 are single/dual/quad,
low-cost, general-purpose comparators. They have a
single-supply operating voltage of 1.8V to 5V. The com-
mon-mode input range extends from -0.1V below the
negative supply to within 0.7V of the positive supply.
They require approximately 60µA per comparator with
a 5V supply and 40µA with a 2.7V supply.
The LMX331H/LMX393H/LMX339H have 2mV of hys-
teresis for noise immunity. This significantly reduces the
chance of output oscillations even with slow-moving
input signals. The LMX331/LMX393/LMX339 and
LMX331H/LMX393H/LMX339H are ideal for automotive
applications because they operate from -40
°C to
+125
°C (see Typical Operating Characteristics).
Applications Information
Hysteresis
Many comparators oscillate in the linear region of oper-
ation because of noise or undesired parasitic feed-
back. This tends to occur when the voltage on one
input is equal or very close to the voltage on the other
input. The LMX331H/LMX393H/LMX339H 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 comparator 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 resis-
tors, using positive feedback (Figure 2). Use the follow-
ing procedure to calculate resistor values:
OUT
IN-
THRESHOLDS
IN+
HYSTERESIS
BAND
V HYST V TL
V TH
Figure 1. Threshold Hysteresis Band (Not to Scale)
PIN
LMX331 LMX393 LMX339
NAME FUNCTION
1 — — IN+ Noninverting Input
2 4 12 V SS Negative Supply (Connect to GND)
3 — — IN- Inverting Input
4 — — OUT Comparator Output (Open-Drain)
5 8 3 V DD Positive Supply
— 1 2 OUTA Comparator A Output (Open-Drain)
— 7 1 OUTB Comparator B Output (Open-Drain)
— 2 4 INA- Comparator A Inverting Input
— 3 5 INA+ Comparator A Noninverting Input
— 5 7 INB+ Comparator B Noninverting Input
— 6 6 INB- Comparator B Inverting Input
— — 8 INC- Comparator C Inverting Input
— — 9 INC+ Comparator C Noninverting Input
— — 10 IND- Comparator D Inverting Input
— — 11 IND+ Comparator D Noninverting Input
— — 13 OUTD Comparator D Output (Open-Drain)
— — 14 OUTC Comparator C Output (Open-Drain)
Pin Description