AD712
1mV
100
90
PD711 BUFF
DRIVING A LARGE CAPACITIVE LOAD
The circuit in Figure 46 uses a 100 Ω isolation resistor that
enables the amplifier to drive capacitive loads exceeding
1500 pF; the resistor effectively isolates the high frequency
feedback from the load and stabilizes the circuit. Low frequency
feedback is returned to the amplifier summing junction via the
low-pass filter formed by the 100 Ω series resistor and the Load
Capacitance C
L
this connection.
00823-044
10
0%
500mV
–10V ADC IN
200ns
4.99kΩ
30pF
+V
IN
0.1µF
+ –
Figure 44. ADC Input Unity Gain Buffer Recovery Times, −10 V ADC IN
4.99kΩ
INPUT
100
90
R
1
2kΩ
10kΩ
20Ω
10
0%
00823-045
C
1
UP TO
00823-046
1500pF
1500pF
1000pF
Figure 46. Circuit for Driving a Large Capacitive Load
500mV
–5V ADC IN
200ns
5V
100
90
Figure 45. ADC Input Unity Gain Buffer Recovery Times, −5 V ADC IN
10
0%
00823-047
Figure 47. Transient Response R
L
= 2 kΩ, C
L
= 500 pF
Rev. G | Page 16 of 20
+
TYPICAL CAPACITANCE
LIMIT FOR VARIOUS
LOAD RESISTORS
–
1mV
PD711 BUFF
AD712
0.1µF
– +
–V
IN
1/2
100Ω
C1
R1
OUTPUT
1µs
AD [ ANALOG DEVICES ]
