Datasheet

ADA4096-2/ADA4096-4 Data Sheet
Rev. D | Page 20 of 24
INPUT OVERVOLTAGE PROTECTION
The ADA409x family inputs are protected from input voltage
excursions up to 32 V outside each rail. This feature is of par-
ticular importance in applications with power supply sequencing
issues that could cause the signal source to be active before the
supplies to the amplifier.
Figure 55 shows the input current limiting capability of the
ADA4096-2 (green curves) compared to using a 5 kΩ series
resistor (red curves).
Figure 55. Input Current Limiting Capability
Figure 55 was generated with the ADA4096-2 in a buffer configu-
ration with the supplies connected to GND (or ±15 V) and the
positive input swept until it exceeds the supplies by 32 V. In general,
input current is limited to 1 mA during positive overvoltage con-
ditions and 200 μA during negative undervoltage conditions. For
example, at an overvoltage of 20 V, t h e ADA4096-2 input current is
limited to 1 mA, providing a current-limit equivalent to a series
20 kΩ resistor. Figure 55 also shows that the current limiting
circuitry is active whether the amplifier is powered or not.
Note that Figure 55 represents input protection under abnormal
conditions only. The correct amplifier operation input voltage
range (IVR) is specified in Table 2 to Table 4.
COMPARATOR OPERATION
Although op amps are quite different from comparators,
occasionally an unused section of a dual or a quad op amp
may be pressed into service as a comparator; however, this is
not recommended for any rail-to-rail output op amps. For rail-
to-rail output op amps, the output stage is generally a ratioed
current mirror with bipolar or MOSFET transistors. With the part
operating open loop, the second stage increases the current drive
to the ratioed mirror to close the loop, but it cannot, which results
in an increase in supply current. With the op amp configured as
a comparator, the supply current can be significantly higher (see
Figure 56).
Figure 56. Comparator Supply Current
7
–48 –40 –32 –24 –16 –8 0 8 16 24 32 40 48
–7
–6
–5
–4
–3
–2
–1
0
1
2
3
4
5
6
INPUT BIAS CURRENT (mA)
V
IN
(V)
V
EE
= –15V
V
EE
= 0V
V
CC
= +15V
LOW RDS
ON
SERIES FET
5kΩ SERIES RESISTOR
09241-047
500
400
300
200
100
0 3632282420
1612
84
0
SUPPLY CURRENT PER AMPLIFIER (µA)
SUPPLY VOLTAGE (V)
V
OUT
= HIGH
V
OUT
= LOW
BUFFER
09241-048