AD8512 Analog Devices, AD8512 Datasheet - Page 15

• 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

Figure 46 shows a scope plot of the output of the AD8510/AD8512/
AD8513 in response to a 400 mV pulse. The circuit is configured in
positive unity gain (worst case) with a load experience of 500 pF.
When the snubber circuit is used, the overshoot is reduced from
55% to less than 3% with the same load capacitance. Ringing is
virtually eliminated, as shown in Figure 47.
Optimum values for R
and input stray capacitance and are determined empirically.
Table 5 shows a few values that can be used as starting points.
Table 5. Optimum Values for Capacitive Loads
C
500 pF
2 nF
5 nF
LOAD
Figure 46. Capacitive Load Drive Without Snubber
Figure 47. Capacitive Load with Snubber Network
V
R
C
R
C
V
C
R
SY
L
L
S
S
SY
L
L
= 10kΩ
= 500pF
= 100Ω
= 1nF
= 500pF
=10kΩ
= ±15V
= ±15V
S
and C
R
100
70
60
S
TIME (1µs/DIV)
TIME (1µs/DIV)
(Ω)
S
depend on the load capacitance
C
1 nF
100 pF
300 pF
S
Rev. I | Page 15 of 20
OPEN-LOOP GAIN AND PHASE RESPONSE
In addition to their impressive low noise, low offset voltage, and
offset current, the AD8510/AD8512/AD8513 have excellent
loop gain and phase response even when driving large resistive
and capacitive loads.
Compared with Competitor A (see Figure 49) under the same
conditions, with a 2.5 kΩ load at the output, the AD8510/AD8512/
AD8513 have more than 8 MHz of bandwidth and a phase margin
of more than 52°.
Competitor A, on the other hand, has only 4.5 MHz of band-
width and 28° of phase margin under the same test conditions.
Even with a 1 nF capacitive load in parallel with the 2 kΩ load
at the output, the AD8510/AD8512/AD8513 show much better
response than Competitor A, whose phase margin is degraded
to less than 0, indicating oscillation.
–30
–10
–20
–30
–10
–20
50
50
10
70
60
40
30
20
10
70
60
40
30
20
Figure 48. Frequency Response of the AD8510/AD8512/AD8513
0
0
10k
10k
Figure 49. Frequency Response of Competitor A
100k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
AD8510/AD8512/AD8513
1M
1M
10M
V
R
C
10M
V
R
C
SY
L
L
SY
L
L
= 2.5kΩ
= 0pF
= 2.5kΩ
= 0pF
= ±15V
= ±15V
50M
50M
45
315
180
135
90
45
315
270
225
180
135
90
270
225
0
–45
–90
0
–45
–90
–135
–135