OP281GSZ Analog Devices Inc, OP281GSZ Datasheet - Page 12

• Manufacturer Part Number: OP281GSZ
• Description: IC OPAMP GP R-R 105KHZ LP 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of OP281GSZ

• Slew Rate: 0.028 V/µs
• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Gain Bandwidth Product: 105kHz
• Current - Input Bias: 3nA
• Voltage - Input Offset: 100µV
• Current - Supply: 3.3µA
• Current - Output / Channel: 12mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: Low Power
• No. Of Amplifiers: 2
• Bandwidth: 105kHz
• Supply Voltage Range: 2.7V To 12V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

OP281/OP481
Low-Side Current Monitor
In the design of power supply control circuits, a great deal of
design effort is focused on ensuring a pass transistor’s long-term
reliability over a wide range of load current conditions. As a
result, monitoring and limiting device power dissipation is of
prime importance in these designs. Figure 7 shows an example
of a 5 V, single-supply current monitor that can be incorporated
into the design of a voltage regulator with fold-back current
limiting or a high current power supply with crowbar protection.
The design capitalizes on the OPx81’s common-mode range
that extends to ground. Current is monitored in the power sup-
ply return path where a 0.1 W shunt resistor, R
very small voltage drop. The voltage at the inverting terminal
becomes equal to the voltage at the noninverting terminal through
the feedback of Q1, which is a 2N2222 or equivalent NPN tran-
sistor. This makes the voltage drop across R1 equal to the voltage
drop across R
directly proportional to the current through R
voltage is given by:
The voltage drop across R2 increases with I
decreases with higher supply current being sensed. For the
element values shown, the V
decreasing from V
Low Voltage Half-Wave and Full-Wave Rectifiers
Because of its quick overdrive recovery time, an OP281 can be
configured as a full-wave rectifier for low frequency (<500 Hz)
applications. Figure 8 shows the schematic.
Figure 8. Single-Supply Full-Wave and Half-Wave
Rectifiers Using an OP281
V
IN
= 2V p-p
Figure 7. Low-Side Load Current Monitor
2k
SENSE
V
R1 = 100k
V
OUT
OUT
A1
3V
EE
. Therefore, the current through Q1 becomes
.
OP281-A
= V
Q1
5V
R
R2
2.49k
R1
100
0.1
EE
SENSE
OUT
-
Ê
Á
Ë
R2
R1
transfer characteristic is –2.5 V/A,
R2 = 100k
5V
¥ R
A2
3V
SENSE
OP281-B
SINGLE
CHANNEL
OPx81
RETURN TO
GROUND
L
SENSE
increasing, so V
¥ I
SENSE
L
, and the output
ˆ
˜
¯
FULL-WAVE
RECTIFIED
OUTPUT
HALF-WAVE
RECTIFIED
OUTPUT
, creates a
OUT
–12–
Amplifier A1 is used as a voltage follower that will track the input
voltage only when it is greater than 0 V. This provides a half-wave
rectification of the input signal to the noninverting terminal of
amplifier A2. When A1’s output is following the input, the invert-
ing terminal of A2 will also follow the input from the virtual
ground between the inverting and noninverting terminals of A2.
With no potential difference across R1, no current flows through
either R1 or R2, therefore the output of A2 will also follow the input.
Now, when the input voltage goes below 0 V, the noninverting
terminal of A2 becomes 0 V. This makes A2 work as an inverting
amplifier with a gain of 1 and provides a full-wave rectified version
of the input signal. A 2 kW resistor in series with A1’s noninverting
input protects the device when the input signal becomes less
than ground.
Battery-Powered Telephone Headset Amplifier
Figure 10 shows how the OP281 can be used as a two-way
amplifier in a telephone headset. One side of the OP281 can be
used as an amplifier for the microphone, while the other side can
be used to drive the speaker. A typical telephone headset uses a
600 W speaker and an electret microphone that requires a supply
voltage and a biasing resistor.
Figure 10. Two-Way Amplifier in a Battery-Powered
Telephone Headset
INPUT
100
2.2k
0%
90
10
3V
1M
3V
Figure 9. Full-Wave Rectified Signal
1 F
1 F
10k
POT.
1 F
ELECTRET
MIC
10k
1 F
1M
0.1 F
1M
1M
11k
50k
3V
3V
OP281-B
300k
3V
20k
20k
OP281-A
SCALE 0.1ms/DIV
SCALE 0.1V/DIV
1 F
3V
Q1
Q2
SPEAKER
MIC OUT
1 F
600
REV. B