OP484FS-REEL7 Analog Devices Inc, OP484FS-REEL7 Datasheet - Page 16

• Manufacturer Part Number: OP484FS-REEL7
• Description: IC,Operational Amplifier,QUAD,BIPOLAR,SOP,14PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of OP484FS-REEL7

• Rohs Status: RoHS non-compliant
• Amplifier Type: General Purpose
• Number Of Circuits: 4
• Output Type: Rail-to-Rail
• Slew Rate: 4 V/µs
• Gain Bandwidth Product: 4.25MHz
• Current - Input Bias: 80nA
• Voltage - Input Offset: 250µV
• Current - Supply: 2.25mA
• Current - Output / Channel: 10mA
• Voltage - Supply, Single/dual (±): 3 V ~ 36 V, ±1.5 V ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• -3db Bandwidth: -
• Other names: OP484FS-REEL7; OP484FS-REEL7TR

OP184/OP284/OP484
As a design aid, Figure 49 shows the total equivalent input noise
of the OP284 and the total thermal noise of a resistor for com-
parison. Note that for source resistance less than 1 kΩ, the
equivalent input noise voltage of the OP284 is dominant.
Because circuit SNR is the critical parameter in the final analysis,
the noise behavior of a circuit is often expressed in terms of its
noise figure, NF. The noise figure is defined as the ratio of a
circuit’s output signal-to-noise to its input signal-to-noise.
An expression of a circuit NF in dB, and in terms of the
operational amplifier voltage and current noise parameters
defined previously, is given by
where:
NF (dB) is the noise figure of the circuit, expressed in decibels.
(e
(i
(e
(4kTR
R
the amplifier.
Calculation of the circuit noise figure is straightforward because
the signal level in the application is not required to determine it.
However, many designers using NF calculations as the basis for
achieving optimum SNR believe that a low noise figure is equal to
low total noise. In fact, the opposite is true, as shown in Figure 50.
The noise figure of the OP284 is expressed as a function of the
source resistance level. Note that the lowest noise figure for the
OP284 occurs at a source resistance level of 10 kΩ. However,
Figure 49 shows that this source resistance level and the OP284
generate approximately 14 nV/√Hz of total equivalent circuit
noise. Signal levels in the application invariably increase to
maximize circuit SNR, which is not an option in low voltage,
single-supply applications.
nOA
S
nOA
nRS
Figure 49. OP284 Equivalent Thermal Noise vs. Total Source Resistance
is the effective, or equivalent, source resistance presented to
)
)
)
2
2
2
NF
is the OP284 noise current spectral power (1 Hz bandwidth).
is the OP284 noise voltage spectral power (1 Hz bandwidth).
is the source resistance thermal noise voltage power =
S
).
100
10
( )
1
100
dB
FREQUENCY = 1kHz
T
A
=
= 25°C
10
log
TOTAL SOURCE RESISTANCE, R
⎡
⎢
⎢
⎣
1
EQUIVALENT NOISE
+
⎛
⎜
⎜
⎝
1k
(
e
OP284 TOTAL
nOA
RESISTOR THERMAL
NOISE ONLY
)
2
(
+
e
nRS
(
i
nOA
)
2
×
10k
R
S
S
)
2
(Ω)
⎞
⎟
⎟
⎠
⎤
⎥
⎥
⎦
100k
Rev. I | Page 16 of 24
Therefore, to achieve optimum circuit SNR in single-supply
applications, it is recommended that an operational amplifier
with the lowest equivalent input noise voltage be chosen, along
with source resistance levels that are consistent with maintaining
low total circuit noise.
OVERDRIVE RECOVERY
The overdrive recovery time of an operational amplifier is the
time required for the output voltage to recover to its linear region
from a saturated condition. The recovery time is important in
applications where the amplifier must recover quickly after a
large transient event. The circuit shown in Figure 51 was used
to evaluate the OP284 overload recovery time. The OP284
takes approximately 2 μs to recover from positive saturation
and approximately 1 μs to recover from negative saturation.
SINGLE-SUPPLY, 3 V INSTRUMENTATION
AMPLIFIER
The low noise, wide bandwidth, and rail-to-rail input/output
operation of the OP284 make it ideal for low supply voltage
applications such as in the two op amp instrumentation amplifier
shown in Figure 52. The circuit uses the classic two op amp
instrumentation amplifier topology with four resistors to set the
gain. The transfer equation of the circuit is identical to that of a
noninverting amplifier. Resistor R2 and Resistor R3 should be
closely matched to each other, as well as to Resistors (R1 + P1)
and Resistor R4 to ensure good common-mode rejection
performance.
10
9
8
7
6
5
4
3
2
1
0
100
Figure 50. OP284 Noise Figure vs. Source Resistance
10V STEP
Figure 51. Output Overload Recovery Test Circuit
V
IN
TOTAL SOURCE RESISTANCE, R
10kΩ
9kΩ
R1
R3
1k
2
3
1/2
OP284
10kΩ
+5V
–5V
R2
4
8
1
10k
FREQUENCY = 1kHz
T
A
= 25°C
S
(Ω)
V
OUT
100k