LM7341_15 datasheet(18/27 Pages) TI

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+VCC

-VEE

VOUT

VIN

LM7341

SNOSAW9B – MAY 2008 – REVISED MARCH 2013

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Figure 54. Non-Inverting Comparator

COMPARATOR WITH HYSTERESIS

The basic comparator configuration may oscillate or produce a noisy output if the applied differential input

voltage is near the comparator's offset voltage. This usually happens when the input signal is moving very slowly

across the comparator's switching threshold. This problem can be prevented by the addition of hysteresis or

positive feedback.

INVERTING COMPARATOR WITH HYSTERESIS

The inverting comparator with hysteresis requires a three resistor network that is referenced to the supply voltage

VCC of the comparator, as shown in Figure 55. When VIN at the inverting input is less than VA, the voltage at the

non-inverting node of the comparator (VIN < VA), the output voltage is high (for simplicity assume VOUT switches

as high as VCC). The three network resistors can be represented as R1||R3 in series with R2. The lower input trip

voltage VA1 is defined as

VA1 = VCCR2 / ((R1||R3) + R2)

(1)

When VIN is greater than VA (VIN > VA), the output voltage is low, very close to ground. In this case the three

network resistors can be presented as R2||R3 in series with R1. The upper trip voltage VA2 is defined as

VA2 = VCC (R2||R3) / ((R1+ (R2||R3)

(2)

The total hysteresis provided by the network is defined as

Delta VA = VA1- VA2

(3)

For example to achieve 50 mV of hysteresis when VCC = 30V set R1 = 4.02 kΩ, R2 = 4.02 kΩ, and R3 = 1.21 MΩ.

With these resistors selected the error due to input bias current is approximately 1 mV. To minimize this error it is

best to use low resistor values on the inputs.

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