OP249_07 Datasheet, PDF (17/20 Pages) Analog Devices – Dual, Precision JFET High Speed Operational Amplifier

As seen in Figure 51, the OP249 has an extremely fast recovery
of 247 ns (to 0.01%) for a 1 mA load transient. The performance
makes it an ideal amplifier for data acquisition systems.
The combination of high speed and excellent dc performance of
the OP249 makes it an ideal amplifier for 12-bit data acquisition
systems. Examining the circuit in Figure 53, one amplifier in the
OP249 provides a stable −5 V reference voltage for the VREF input of
the ADC912. The other amplifier in the OP249 performs high
speed buffering of the input of the ADC.
By examining the worst-case transient voltage error at the AIN
node of the ADC, it is shown that the OP249 recovers in less
than 100 ns (see Figure 52). The fast recovery is due to both the
wide bandwidth and low dc output impedance of the OP249.
247.4ns
100
90
5mV
100
90
OP249
10
0%
100ns
Figure 52. Worst-Case Transient Voltage at Analog In Occurs at
the Half-Scale Point of the ADC; the OP249 Buffers the
ADC Input from Figure 53 and Recovers in <100 ns
10
0%
2mV
2V
100ns
Figure 51. Transient Recovery Time of the OP249 from
a 1 mA Load Transient to 0.01%
ANALOG
INPUT
+15V
0.1µF
2
V_IN
REF02
V_OUT 6
GND
4
+15V
0.1µF
3
8
1/2
OP249
2
4
1
0.1µF
–15V
0.1µF
+5V
–15V
10µF||0.1µF
10µF||0.1µF
24
23
1 A_IN
RD 20
ADC912A
CLK IN 17
2 V_REFIN
BUSY 22
AGND DGND HBEN CS
3
12
19
21
5
1/2
10Ω
OP249 ¹
6
–5V
10µF||0.1µF
Figure 53. OP249 Dual Amplifiers Provide Both Stable −5 V Reference Input and Buffers Input to ADC912A
Rev. F | Page 17 of 20