LM339-TR 查看數據表（PDF） - Unspecified

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LM339-TR

36V Low Power Dual/Quad Differential Comparators

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LM393/LM339

36V Low Power Dual/Quad Differential Comparators

Proper Board Layout

The LM393/339 family is a series of fast-switching, high-speed comparator and requires high-speed layout

considerations. For best results, the following layout guidelines should be followed:

1. Use a printed circuit board (PCB) with a good, unbroken low-inductance ground plane.

2. Place a decoupling capacitor (0.1μF ceramic, surface-mount capacitor) as close as possible to supply.

3. On the inputs and the output, keep lead lengths as short as possible to avoid unwanted parasitic feedback

around the comparator. Keep inputs away from the output.

4. Solder the device directly to the PCB rather than using a socket.

5. For slow-moving input signals, take care to prevent parasitic feedback. A small capacitor (1000 pF or less) placed

between the inputs can help eliminate oscillations in the transition region. This capacitor causes some

degradation to propagation delay when the impedance is low. The topside ground plane should be placed

between the output and inputs.

6. The ground pin ground trace should run under the device up to the bypass capacitor, thus shielding the inputs

from the outputs.

Typical Applications

IR Receiver

The LM393/339 is an ideal candidate to be used as an infrared receiver shown in Figure 6. The infrared photo diode

creates a current relative to the amount of infrared light present. The current creates a voltage across RD. When this

voltage level cross the voltage applied by the voltage divider to the inverting input, the output transitions. Optional Ro

provides additional hysteresis for noise immunity.

VDD

R1

Ro

LM393

Vo

R2

RD

Figure 6. IR Receiver

Relaxation Oscillator

A relaxation oscillator using LM393/339 is shown in Figure 7. Resistors R1 and R2 set the bias point at the

comparator's inverting input. The period of oscillator is set by the time constant of R4 and C1. The maximum frequency

is limited by the large signal propagation delay of the comparator. LM393/339’s low propagation delay guarantees the

high frequency oscillation.

If the inverted input (VC1) is lower than the non-inverting input (VA), the output is high which charges C1 through R4

until VC1 is equal to VA. The value of VA at this point is

VA1



VDD  R 2

R 1 || R 3  R 2

At this point the comparator switches pulling down the output to the negative rail. The value of VA at this point is

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Rev. B.2

9

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