AD8512 Analog Devices, AD8512 Datasheet - Page 13

• Manufacturer Part Number: AD8512
• Description: Low Noise, Low Input Bias Current, Wide Bandwidth Precision JFET Dual Op Amp
• Manufacturer: Analog Devices

Specifications of AD8512

• -3db Bandwidth: 8MHz
• Slew Rate: 20V/µs
• Vos: 80µV
• Ib: 21pA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 7.6nV/rtHz
• Vcc-vee: 9V to 36V
• Isy Per Amplifier: 2.5mA
• Packages: SOIC,SOP

GENERAL APPLICATION INFORMATION
INPUT OVERVOLTAGE PROTECTION
The AD8510/AD8512/AD8513 have internal protective
circuitry that allows voltages as high as 0.7 V beyond the
supplies to be applied at the input of either terminal without
causing damage. For higher input voltages, a series resistor is
necessary to limit the input current. The resistor value can be
determined from the formula
With a very low offset current of <0.5 nA up to 125°C, higher
resistor values can be used in series with the inputs. A 5 kΩ
resistor protects the inputs from voltages as high as 25 V
beyond the supplies and adds less than 10 μV to the offset.
OUTPUT PHASE REVERSAL
Phase reversal is a change of polarity in the transfer function of
the amplifier. This can occur when the voltage applied at the
input of an amplifier exceeds the maximum common-mode
voltage.
Phase reversal can cause permanent damage to the device and
can result in system lockups. The AD8510/AD8512/AD8513 do
not exhibit phase reversal when input voltages are beyond the
supplies.
TOTAL HARMONIC DISTORTION (THD) + NOISE
The AD8510/AD8512/AD8513 have low THD and excellent gain
linearity, making these amplifiers great choices for precision
circuits with high closed-loop gain and for audio application
circuits. Figure 42 shows that the AD8510/AD8512/AD8513 have
approximately 0.0005% of total distortion when configured in
positive unity gain (the worst case) and driving a 100 kΩ load.
V
IN
R
−
S
V
S
≤
5
mA
Figure 41. No Phase Reversal
TIME (20µs/DIV)
V
IN
V
OUT
V
A
R
SY
V
L
= 10kΩ
= 1
= ±5V
Rev. I | Page 13 of 20
TOTAL NOISE INCLUDING SOURCE RESISTORS
The low input current noise and input bias current of the
AD8510/AD8512/AD8513 make them the ideal amplifiers for
circuits with substantial input source resistance. Input offset
voltage increases by less than 15 nV per 500 Ω of source
resistance at room temperature. The total noise density of the
circuit is
where:
e
i
R
k is Boltzmann’s constant (1.38 × 10
T is the ambient temperature in Kelvin (T = 273 + °C).
For R
of the AD8510/AD8512/AD8513 is so low that its total density
does not become a significant term unless R
165 MΩ, an impractical value for most applications.
The total equivalent rms noise over a specific bandwidth is
expressed as
where BW is the bandwidth in hertz.
Note that the previous analysis is valid for frequencies larger
than 150 Hz and assumes flat noise above 10 kHz. For lower
frequencies, flicker noise (1/f) must be considered.
n
n
S
is the input current noise density of the parts.
is the input voltage noise density of the parts.
is the source resistance at the noninverting terminal.
e
e
0.0001
S
nTOTAL
0.001
nTOTAL
< 3.9 kΩ, e
0.01
20
=
V
R
BW = 22kHz
=
SY
L
= 100kΩ
e
= ±5V
e
nTOTAL
n
n
Figure 42. THD + N vs. Frequency
2
dominates and e
+
100
(
i
n
R
AD8510/AD8512/AD8513
BW
S
)
FREQUENCY (Hz)
2
+
4
kTR
nTOTAL
–23
1k
S
J/K).
≈ e
S
n
. The current noise
is greater than
10k
20k