AD620BRZ-RL Analog Devices Inc, AD620BRZ-RL Datasheet - Page 16

• Manufacturer Part Number: AD620BRZ-RL
• Description: IC,Instrumentation Amplifier,SINGLE,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD620BRZ-RL

• Design Resources: Low Cost Programmable Gain Instrumentation Amplifier Circuit Using ADG1611 and AD620 (CN0146)
• Amplifier Type: Instrumentation
• Number Of Circuits: 1
• Slew Rate: 1.2 V/µs
• -3db Bandwidth: 1MHz
• Current - Input Bias: 500pA
• Voltage - Input Offset: 15µV
• Current - Supply: 900µA
• Current - Output / Channel: 18mA
• Voltage - Supply, Single/dual (±): 4.6 V ~ 36 V, ±2.3 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD620
Precision V-I Converter
The AD620, along with another op amp and two resistors,
makes a precision current source (Figure 42). The op amp
buffers the reference terminal to maintain good CMR. The
output voltage, V
converts it to a current. This current, less only the input bias
current of the op amp, then flows out to the load.
GAIN SELECTION
The AD620’s gain is resistor-programmed by R
precisely, by whatever impedance appears between Pins 1 and 8.
The AD620 is designed to offer accurate gains using 0.1% to 1%
resistors. Table 4 shows required values of R
Note that for G = 1, the R
any arbitrary gain, R
To minimize gain error, avoid high parasitic resistance in series
with R
than 10 ppm/°C—for the best performance.
Table 4. Required Values of Gain Resistors
1% Std Table
Value of R
49.9 k
12.4 k
5.49 k
2.61 k
1.00 k
499
249
100
49.9
Figure 42. Precision Voltage-to-Current Converter (Operates on 1.8 mA, ±3 V)
V
V
IN+
IN–
R
G
G
; to minimize gain drift, R
=
R
G
49
G
(Ω)
G
4 .
−
k
1
I =
Ω
L
X
, of the AD620 appears across R1, which
3
8
1
2
V
Calculated
Gain
1.990
4.984
9.998
19.93
50.40
100.0
199.4
495.0
991.0
R1
x
G
=
can be calculated by using the formula:
AD620
[(V
+V
–V
IN+
G
7
4
S
S
pins are unconnected (R
) – (V
R1
5
IN–
)] G
G
0.1% Std Table
Value of R
49.3 k
12.4 k
5.49 k
2.61 k
1.01 k
499
249
98.8
49.3
should have a low TC—less
6
AD705
G
+ V –
G
(Ω )
R1
for various gains.
X
G
, or more
G
LOAD
Calculated
Gain
2.002
4.984
9.998
19.93
49.91
100.0
199.4
501.0
1,003.0
= ∞). For
I
L
Rev. G | Page 16 of 20
INPUT AND OUTPUT OFFSET VOLTAGE
The low errors of the AD620 are attributed to two sources,
input and output errors. The output error is divided by G when
referred to the input. In practice, the input errors dominate at
high gains, and the output errors dominate at low gains. The
total V
REFERENCE TERMINAL
The reference terminal potential defines the zero output voltage
and is especially useful when the load does not share a precise
ground with the rest of the system. It provides a direct means of
injecting a precise offset to the output, with an allowable range
of 2 V within the supply voltages. Parasitic resistance should be
kept to a minimum for optimum CMR.
INPUT PROTECTION
The AD620 features 400 Ω of series thin film resistance at its
inputs and will safely withstand input overloads of up to ±15 V
or ±60 mA for several hours. This is true for all gains and power
on and off, which is particularly important since the signal
source and amplifier may be powered separately. For longer
time periods, the current should not exceed 6 mA
(I
clamping the inputs to the supplies (using a low leakage diode
such as an FD333) will reduce the required resistance, yielding
lower noise.
RF INTERFERENCE
All instrumentation amplifiers rectify small out of band signals.
The disturbance may appear as a small dc voltage offset. High
frequency signals can be filtered with a low pass R-C network
placed at the input of the instrumentation amplifier. Figure 43
demonstrates such a configuration. The filter limits the input
signal according to the following relationship:
where C
C
signal. Any mismatch in R × C
CMRR. To avoid inadvertently reducing CMRR-bandwidth
performance, make sure that C
smaller than C
larger C
D
IN
affects the difference signal. C
≤ V
Total Error RTI = input error + (output error/G)
Total Error RTO = (input error × G) + output error
FilterFreq
FilterFreq
OS
IN
D
D
for a given gain is calculated as
/400 Ω). For input overloads beyond the supplies,
:C
≥10C
C
ratio.
D
CM
DIFF
C.
. The effect of mismatched C
=
=
2
2
π
π
RC
1
R
2 (
C
C
1
D
C
C
+
will degrade the AD620’s
is at least one magnitude
C
C
affects the common-mode
C
)
C
s is reduced with a