ADA4091-2 Analog Devices, ADA4091-2 Datasheet - Page 15

• Manufacturer Part Number: ADA4091-2
• Description: Dual, Precision, Micropower, OVP, Rail-to-Rail Input/Output Operational Amplifier
• Manufacturer: Analog Devices

Specifications of ADA4091-2

• -3db Bandwidth: 1.27MHz
• Slew Rate: 0.46V/µs
• Vos: 35µV
• Ib: 50nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 25nV/rtHz
• Vcc-vee: 3V to 30V
• Isy Per Amplifier: 200µA
• Packages: CSP,SOIC

INPUT OVERVOLTAGE PROTECTION
The ADA4091-x has two different ESD circuits for enhanced
protection, as shown in Figure 48.
One circuit is a series resistor of 5 kΩ to the internal inputs and
diodes (D1 and D2 or D5 and D6) from the internal inputs to
the supply rails. The other protection circuit is a circuit with
two DIACs (D3 and D4 or D7 and D8) to the supply rails. A
DIAC can be considered a bidirectional Zener diode with a
transfer characteristic, as shown in Figure 49.
–1
–2
–3
5
4
3
2
1
0
–50
–40
Figure 48. Complete Input Protection Network
D7 R2
Figure 49. DIAC Transfer Characteristic
–30
D8
D6
–20
D5
D3
–10
VOLTAGE (V)
R1
D4
D2
0
D1
10
+V
–V
20
30
40
50
Rev. F | Page 15 of 20
For a worst-case design analysis, consider two cases. The
ADA4091-x has a normal ESD structure from the internal op
amp inputs to the supply rails. In addition, it has 42 V DIACs
from the external inputs to the rails, as shown in Figure 47.
Therefore, two conditions need to be considered to determine
which case is the limiting factor.
•
•
Additional resistance can be added externally in series with
each input to protect against higher peak voltages; however, the
additional thermal noise of the resistors must be considered.
The flatband voltage noise of the ADA4091-x is approximately
24 nV/√Hz, and a 5 kΩ resistor has a noise of 9 nV/√Hz. Adding
an additional 5 kΩ resistor increases the total noise by less than
15% root sum square (rss). Therefore, maintain resistor values
below this value (5 kΩ) when overall noise performance is critical.
Note that this represents input protection under abnormal con-
ditions only. The correct amplifier operation input voltage range
(IVR) is specified in Table 2, Table 3, and Table 4.
Condition 1. Consider, for example, that when operating
on ±15 V, the inputs can go +42 V above the negative
supply rail. With the −V pin equal to −15 V, +42 V above
this supply (the negative supply) is +27 V.
Condition 2. There is a restriction on the input current of
5 mA through a 5 kΩ resistor to the ESD structure to the
positive rail. In Condition 1, +27 V through the 5 kΩ
resistor to +15 V gives a current of 2.4 mA. Thus, the
DIAC is the limiting factor. If the ADA4091-x supply
voltages are changed to ±5 V, then −5 V + 42 V = +37 V.
However, +5 V + (5 kΩ × 5 mA) = 30 V. Thus, the normal
resistor diode structure is the limitation when running on
lower supply voltages.
ADA4091-2/ADA4091-4