MAX953ESA Maxim Integrated Products, MAX953ESA Datasheet - Page 11

• Manufacturer Part Number: MAX953ESA
• Description: Op Amps Op Amp / Comparator / Reference
• Manufacturer: Maxim Integrated Products

Specifications of MAX953ESA

• Lead Free Status / Rohs Status: No

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
capacitor to ground. Do not bypass the reference output.
The circuit in Figure 4 is useful as a front end for low-
frequency RF alarms. The unshielded inductor (M7334-
ND from Digikey) is used with capacitors C1
C1
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
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.
The circuit in Figure 5 uses the MAX952 as a pin photo-
diode preamplifier and discriminator for an infrared
Figure 5. Infrared Receiver Application
C
SE307-C
NEC
51Ω
in a resonant circuit to provide frequency selectivity.
10kHz
5V
R1 x C1 = R2 x C2 =
P-P
Low-Frequency Radio Receiver for
LAYOUT-SENSITIVE AREA
49.9kΩ, 1%
MAX952
Remote Controls and Data Links
Infrared Receiver Front End for
NEC
PH302B
R1
A
______________________________________________________________________________________
2π f
1
150pF, 5%
R1
49.9kΩ, 1%
C
Applications Circuits
15pF, 5%
B
0.1µF
C1
Power-Supply Bypassing
C2
Alarms and Detectors
R2
1.0MΩ,1%
AMP
100kΩ
Op Amp + Comparator + Reference
30kΩ
0.1µF
1.2V
DD
Ultra-Low-Power, Single-Supply
REF
with a. 0.1µF
V
CC
A
COMP
, C1
= 5V
10MΩ
B
, and
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.
The high-impedance CMOS inputs of the MAX951–
MAX954 op amps 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
Figure 6. Sensor Preamp and Alarm Trigger Application
RADIOACTIVE
IONIZATION
CHAMBER
SMOKE SENSOR
Sensor Preamp and Alarm Trigger for
LAYOUT-SENSITIVE AREA
AMP
Smoke Detectors
4.7MΩ
5.1MΩ
MAX953
COMP
V
CC
11