Datasheet

Data Sheet ADA4610-2
Rev. B | Page 15 of 20
APPLICATIONS INFORMATION
COMPARATOR OPERATION
Although op amps are quite different from comparators,
occasionally an unused section of a dual or a quad op amp may
be used as a comparator; however, this is not recommended for
any rail-to-rail output op amp. 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. However, the second stage cannot close the loop,
which results in an increase in supply current. With the op amp
configured as a comparator, the supply current can be signifi-
cantly higher (see Figure 45). Configuring an unused section as
a voltage follower with the noninverting input connected to a
voltage within the input voltage range is recommended. The
ADA4610-2 has a unique output stage design that reduces the
excess supply current, but does not entirely eliminate this effect
when the op amp is operating open loop.
8
7
6
5
4
3
2
1
0
0 4 8 12 16 20 24 28 32
SUPPLY VOLTAGE (V)
I
SY
FOR BOTH AMPLIFIERS (mA)
09646-053
COMPARATOR, V
OUT
= LOW
FOLLOWER
COMPARATOR, V
OUT
= HIGH
Figure 45. Supply Current vs. Supply Voltage
1++ –
D31
Q28
Q27
V
OUT
09646-054
V
EE
Q15Q14
Q13 Q17Q16Q23
Q29Q30
J1 J2
Q9
Q5
Q4
Q8
Q1
Q6
Q7
Q25
Q24
Q18
Q12
I
2
I
3
I
4
C2
C1
C3
DE1
V
IN+
V
IN–
C4
A2A1
R16
R7R6
R3
R5
R2
R10 R11
RC4
D26
R16
V
CC
DE5
DE6
DE3
DE2
DE4
Figure 46. Simplified Schematic