AD8609 Analog Devices, AD8609 Datasheet - Page 12

• Manufacturer Part Number: AD8609
• Description: Precision Quad MicroPower Rail-to-Rail Input/Output Amplifier
• Manufacturer: Analog Devices

Specifications of AD8609

• -3db Bandwidth: 400kHz
• Slew Rate: 0.1V/µs
• Vos: 12µV
• Ib: 0.2pA
• # Opamps Per Pkg: 4
• Input Noise (nv/rthz): 22nV/rtHz
• Vcc-vee: 1.8V to 5V
• Isy Per Amplifier: 50µA
• Packages: SOIC,SOP

AD8603/AD8607/AD8609
APPLICATIONS
NO PHASE REVERSAL
The AD8603/AD8607/AD8609 do not exhibit phase inversion
even when the input voltage exceeds the maximum input
common-mode voltage. Phase reversal can cause permanent
damage to the amplifier, resulting in system lockups. The
AD8603/AD8607/AD8609 can handle voltages of up to 1 V
over the supply.
INPUT OVERVOLTAGE PROTECTION
If a voltage 1 V higher than the supplies is applied at either
input, the use of a limiting series resistor is recommended. If
both inputs are used, each one should be protected with a
series resistor.
To ensure good protection, the current should be limited to a
maximum of 5 mA. The value of the limiting resistor can be
determined from the following equation:
DRIVING CAPACITIVE LOADS
The AD8603/AD8607/AD8609 are capable of driving large
capacitive loads without oscillating. Figure 42 shows the output
of the AD8603/AD8607/AD8609 in response to a 100 mV input
signal, with a 2 nF capacitive load.
Although it is configured in positive unity gain (the worst case),
the AD8603 shows less than 20% overshoot. Simple additional
circuitry can eliminate ringing and overshoot.
One technique is the snubber network, which consists of a
series RC and a resistive load (see Figure 43). With the snubber
in place, the AD8603/AD8607/AD8609 are capable of driving
capacitive loads of 2 nF with no ringing and less than 3%
overshoot.
(V
IN
− V
S
)/(R
S
+ 200 Ω) ≤ 5 mA
Figure 41. No Phase Response
V
IN
TIME (4µs/DIV)
V
OUT
V
V
A
R
S
IN
V
L
= ±2.5V
= 1
= 10kΩ
= 6V p-p
Rev. C | Page 12 of 16
The use of the snubber circuit is usually recommended for unity
gain configurations. Higher gain configurations help improve
the stability of the circuit. Figure 44 shows the same output
response with the snubber in place.
Optimum values for R
Table 5 lists a few starting values.
Table 5. Optimum Values for the Snubber Network
C
100 to ~500
1500
1600 to ~2000
L
Figure 42. Output Response to a 2 nF Capacitive Load, Without Snubber
(pF)
Figure 44. Output Response to a 2 nF Capacitive Load with Snubber
200mV
Figure 43. Snubber Network
S
R
500
100
400
+
–
and C
S
(Ω)
V
V
V–
V+
EE
CC
S
are determined empirically;
47pF
150Ω
C
R
S
S
C
V
V
C
R
V
V
C
R
R
C
C
330
L
680
100
S
IN
L
L
SY
IN
L
L
S
S
S
= ±0.9V
= 2nF
= 10kΩ
= 100mV
= 2nF
= 10kΩ
= 150Ω
= 470pF
= 100mV
= ±0.9V
(pF)