MAX954 データシートの表示（PDF） - Maxim Integrated

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MAX954

Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference

Maxim Integrated 

MAX951–MAX954

Ultra-Low-Power, Single-Supply

Op Amp + Comparator + Reference

10kHz

5VP-P

NEC

SE307-C

51Ω

C2

15pF, 5%

NEC

PH302B

R2

1.0MΩ,1%

R1A

C1

49.9kΩ, 1% 150pF, 5%

R1B

49.9kΩ, 1%

AMP

100kΩ

MAX952 0.1µF

LAYOUT-SENSITIVE AREA

R1 x C1 = R2 x C2 = 1

2� fC

Figure 5. Infrared Receiver Application

VCC = 5V

0.1µF

30kΩ

10MΩ

1.2V

COMP

REF

Power-Supply Bypassing

Power-supply bypass capacitors are not required if the

supply impedance is low. For single-supply applications,

it is good general practice to bypass VDD with a 0.1μF

capacitor to ground. Do not bypass the reference output.

Applications Circuits

Low-Frequency Radio Receiver for

Alarms and Detectors

The circuit in Figure 4 is useful as a front end for low-fre-

quency RF alarms. The unshielded inductor (M7334-ND

from Digikey) is used with capacitors C1A, C1B, and C1C

in a resonant circuit to provide frequency selectivity. The

op amp from a MAX952 amplifies the signal received. The

comparator improves noise immunity, provides a signal

strength threshold, and translates the received signal into

a pulse train. Carrier frequencies are limited to around

10kHz. 10kHz is used in the example in Figure 4.

The layout and routing of components for the amplifier

should be tight to minimize 60Hz interference and cross-

talk from the comparator. Metal shielding is recommended

to prevent RFI from the comparator or digital circuitry from

exciting the receiving antenna. The transmitting antenna

can be long parallel wires spaced about 7.2cm apart,

with equal but opposite currents. Radio waves from this

antenna will be detectable when the receiver is brought

within close proximity, but cancel out at greater distances.

Infrared Receiver Front End for

Remote Controls and Data Links

The circuit in Figure 5 uses the MAX952 as a pin pho-

todiode preamplifier and discriminator for an infrared

receiver. The op amp is configured as a Delyiannis-Friend

RADIOACTIVE

IONIZATION

CHAMBER

AMP

SMOKE SENSOR

LAYOUT-SENSITIVE AREA

MAX953

VCC

4.7MΩ

COMP

5.1MΩ

Figure 6. Sensor Preamp and Alarm Trigger Application

bandpass filter to reduce disturbances from noise and

eliminate low-frequency interference from sunlight, fluo-

rescent lights, etc. This circuit is applicable for TV remote

controls and low-frequency data links up to 20kbps.

Carrier frequencies are limited to around 10kHz. 10kHz is

used in the example circuit.

Component layout and routing for the amplifier should

be tight to reduce stray capacitance, 60Hz interference,

and RFI from the comparator. Crosstalk from comparator

edges will distort the amplifier signal. In order to minimize

the effect, a lowpass RC filter is added to the connection

from the reference to the noninverting input of the op amp.

Sensor Preamp and Alarm Trigger for

Smoke Detectors

The high-impedance CMOS inputs of the MAX951–

MAX954 op amps are ideal for buffering high-impedance

sensors, such as smoke detector ionization chambers,

piezoelectric transducers, gas detectors, and pH sen-

sors. Input bias currents are typically less than 3pA at

room temperature. A 5μA typical quiescent current for the

MAX953 will minimize battery drain without resorting to

complex sleep schemes, allowing continuous monitoring

and immediate detection.

Ionization-type smoke detectors use a radioactive source,

such as Americium, to ionize smoke particles. A posi-

tive voltage on a plate attached to the source repels the

positive smoke ions and accelerates them toward an outer

electrode connected to ground. Some ions collect on an

intermediate plate. With careful design, the voltage on this

plate will stabilize at a little less than one-half the supply

voltage under normal conditions, but rise higher when

smoke increases the ion current. This voltage is buffered

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