OP162 Datasheet, PDF (11/16 Pages) Analog Devices – 15 MHz Rail-to-Rail Operational Amplifiers

OP162/OP262/OP462
2V
100
90
500ns
10
0%
50mV
V_S = 5V
A_V = 1
R_L = 10k⍀
Figure 32. Oscilloscope Photo of V_S and V_OUT
+1
0 TO +5V ⁺
SQUARE –
OP462
V_OUT
10k⍀
Figure 33. Test Circuit for Power On Settling Time
Capacitive Load Drive
The OP162/OP262/OP462 is a high speed, extremely accurate
device and can tolerate some capacitive loading at its output.
As load capacitance increases, however, the unity-gain band-
width of the device will decrease. There will also be an increase
in overshoot and settling time for the output. Figure 35 shows
an example of this with the device configured for unity gain and
driving a 10 kW resistor and 300 pF capacitor placed in parallel.
By connecting a series R-C network, commonly called a “snub-
ber” network, from the output of the device to ground, this
ringing can be eliminated and overshoot can be significantly
reduced. Figure 34 shows how to set up the snubber network,
and Figure 36 shows the improvement in output response with
the network added.
+5V
OPx62
V_OUT
V_IN
R_X
C_L
C_X
Figure 34. Snubber Network Compensation for Capacitive
Loads
V_S = 5V
100
A_V = 1
90
C_L = 300pF
R_L = 10k⍀
10
0%
50mV
1␮s
Figure 35. A Photo of a Ringing Square Wave
V_S = 5V
100
A_V = 1
90
C_L = 300pF
R_L = 10k⍀
10
0%
50mV
WITH SNUBBER:
R_X = 140⍀
C_X = 10nF
1␮s
Figure 36. A Photo of a Nice Square Wave at the Output
The network operates in parallel with the load capacitor, C_L,
and provides compensation for the added phase lag. The actual
values of the network resistor and capacitor are determined
empirically to minimize overshoot while maximizing unity-gain
bandwidth. Table I shows a few sample snubber networks for
large load capacitors:
Table I. Snubber Networks for Large Capacitive Loads
C_LOAD
<300 pF
500 pF
1 nF
10 nF
R_X
140 W
100 W
80 W
10 W
C_X
10 nF
10 nF
10 nF
47 nF
Obviously, higher load capacitance will also reduce the unity-
gain bandwidth of the device. Figure 37 shows a plot of unity-
gain bandwidth versus capacitive load. The snubber network
will not provide any increase in bandwidth, but it will substan-
tially reduce ringing and overshoot, as shown in the difference
between Figures 35 and 36.
10
9
8
7
6
5
4
3
2
1
0
10pF
100pF
1nF
10nF
C_LOAD
Figure 37. Unity Gain Bandwidth vs. C_LOAD
Total Harmonic Distortion and Crosstalk
The OPx62 device family offers low total harmonic distortion.
This makes it an excellent device choice for audio applications.
Figure 38 shows a graph of THD plus noise figures at 0.001%
for the OP462.
Figure 39 shows a graph of the worst case crosstalk between two
amplifiers in the OP462 device. A 1 V rms signal is applied to
one amplifier while measuring the output of an adjacent ampli-
fier. Both amplifiers are configured for unity gain and supplied
with ± 2.5 V.
REV. D
–11–