OP285 Datasheet, PDF (8/16 Pages) Analog Devices – Dual 9 MHz Precision Operational Amplifier

OP285
+15V
0.1␮F
3₊ ⁸
1/2
1
OP285
2_–
4
0.1␮F
*
–15V
+ 7A13 PLUG-IN
– 7A13 PLUG-IN
TTL
INPUT
300pF
15V
1.5k⍀
1k⍀
2N3904
⌬I_OUT
|V_REF|
1k⍀
1N4148
1.8k⍀
15V
2N2907
1k⍀
220⍀
10␮F
+
0.1␮F
*NOTE
DECOUPLE CLOSE
TOGETHER ON GROUND PLAN
WITH SHORT LEAD LENGTHS.
0.01␮F
0.47␮F
V_REF
(–1V)
Figure 5. Transient Output Load Current Test Fixture
A1
100
TTL CTRL ⁹⁰
(5V/ DIV)
1,2 V
10V
V_{OUT 10}
(2MV/ DIV) 0%
5V
2MV
T
138.9^NS
50NS
Measuring Settling Time
The design of OP285 combines high slew rate and wide gain-
bandwidth product to produce a fast-settling (ts < l µs) amplifier
for 8- and 12-bit applications. The test circuit designed to measure
the settling time of the OP285 is shown in Figure 7. This test
method has advantages over false-sum node techniques in that
the actual output of the amplifier is measured, instead of an
error voltage at the sum node. Common-mode settling effects
are exercised in this circuit in addition to the slew rate and
bandwidth effects measured by the false-sum-node method. Of
course, a reasonably flat-top pulse is required as the stimulus.
The output waveform of the OP285 under test is clamped by
Schottky diodes and buffered by the JFET source follower.
The signal is amplified by a factor of ten by the OP260 and
then Schottky-clamped at the output to prevent overloading
the oscilloscope’s input amplifier. The OP41 is configured as
a fast integrator which provides overall dc offset nulling.
High Speed Operation
As with most high speed amplifiers, care should be taken with
supply decoupling, lead dress, and component placement. Rec-
ommended circuit configurations for inverting and noninverting
applications are shown in Figures 8 and Figure 9.
+15V
10␮F
+
0.1␮F
2– 8
1/2
1
V_OUT
V_IN
3
OP285
+
4
R_L
15k⍀
0.1␮F
Figure 6. OP285’s Output Load Current Recovery Time
10␮F
16–20V
–+
0.1␮F
V+
DUT
V–
0.1␮F
+–
16–20V
؎5V
R_L
1k⍀
D1
–15V
Figure 8. Unity Gain Follower
+15V
1k⍀
D3
2N4416 _{1/2 OP260AJ}
D2
R_F
2k⍀
R_G
222⍀
10k⍀
10k⍀
OUTPUT
(TO SCOPE)
D4
1␮F
IC2
1N4148
2N2222A
15k⍀
–15V
750⍀
SCHOTTKY DIODES D1–D4 ARE
HEWLETT-PACKARD HP5082-2835
IC1 IS 1/2 OP260AJ
IC2 IS PMI OP41EJ
Figure 7. OP285’s Settling Time Test Fixture
–8–
REV. A