參數(shù)資料
型號: MAX951MJA
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 運動控制電子
英文描述: Scan Test Devices With Octal Buffers 28-LCCC -55 to 125
中文描述: OP-AMP, 5000 uV OFFSET-MAX, 20 MHz BAND WIDTH, CDIP8
封裝: CERDIP-8
文件頁數(shù): 11/12頁
文件大?。?/td> 114K
代理商: MAX951MJA
Power-S upply 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 V
DD
with a. 0.1μF
capacitor to ground. Do not bypass the reference output.
________________Applic ation Circ uits
Low-Frequenc y Radio Rec eiver for
Alarms and Detec tors
Figure 4’s circuit is useful as a front end for low-frequen-
cy RF alarms. The unshielded inductor (M7334-ND from
Digikey) is used with capacitors C1
A
, C1
B
, and C1
C
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
crosstalk from the comparator. Metal shielding is rec-
ommended to prevent RFI from the comparator or digi-
tal 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 can-
cel out at greater distances.
Infrared Rec eiver 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 bandpass filter to reduce disturbances from
noise and eliminate low-frequency interference from
sunlight, fluorescent lights, etc. This circuit is applica-
ble 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 interfer-
ence, 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 non-
inverting input of the op amp.
S ensor Preamp and Alarm T rigger for
S moke Detec tors
The high-impedance CMOS inputs of the MAX951–
MAX954 op amp are ideal for buffering high-imped-
ance sensors, such as smoke detector ionization cham-
bers, piezoelectric transducers, gas detectors, and pH
sensors. 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 continu-
ous monitoring and immediate detection.
Ionization-type smoke detectors use a radioactive source,
such as Americium, to ionize smoke particles. A positive
voltage on a plate attached to the source repels the posi-
tive 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
M
Ultra-Low-Power, S ingle-S upply
Op Amp + Comparator + Referenc e
______________________________________________________________________________________
11
REF
0.1
μ
F
0.1
μ
F
π
f
C
10M
100k
1.2V
30k
V
CC
= 5V
COMP
AMP
C2
15pF, 5%
10kHz,
5Vp-p
C1
150pF,
5%
NEC
PH302B
NEC
SE307-C
51
R1
49.9k
1%
R1
B
49.9k
1%
R2
1.0M,
1%
LAYOUT-SENSITIVE AREA
MAX952
R1 x C1 = R 2
5.1M
V
CC
LAYOUT-SENSITIVE AREA
RADIOACTIVE
IONIZATION
CHAMBER
SMOKE SENSOR
COMP
4.7M
AMP
MAX953
Figure 5. Infrared Receiver Application
Figure 6. Sensor Preamp and Alarm Trigger Application
相關(guān)PDF資料
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