June 2005 7 MIC7122
MIC7122 Micrel
capacitance C
IN
. The value of C
FB
is determined by first
estimating C
IN
and then applying the following formula:
R
IN
× C
IN
≤ R
FB
× C
FB
V
IN
C
FB
R
FB
V
OUT
C
IN
R
IN
Figure 2. Cancelling Feedback Phase Lag
Since a significant percentage of C
IN
may be caused by board
layout, it is important to note that the correct value of C
FB
may
change when changing from a breadboard to the final circuit
layout.
Typical Circuits
Some single-supply, rail-to-rail applications for which the
MIC7122 is well suited are shown in the circuit diagrams of
Figures 3 through 7.
R2
910k
R1
100k
V
OUT
0V to V+
V+
V
IN
1
⁄2 MIC7122
0V to
V+
A
V
Figure 3a. Noninverting Amplifier
0
100
0 100
V
OUT
(V)
V
IN
(V)
V+
A1
R2
R1
V
=+ ≈10
Figure 3b. Noninverting Amplifier Behavior
V
OUT
0V to V+
V+
V
IN
0V to V+
1
⁄
2
MIC7122
V
OUT
= V
IN
Figure 4. Voltage Follower/Buffer
V
OUT
0V to V+
V+
V
IN
0V to 2V
1
⁄
2
MIC7122
R
S
10Ω
1
⁄
2
W
Load
V
S
0.5V to Q1 V
CEO(sus)
I
OUT
Q1
2N3904
V
CEO
= 40V
I
C(max)
= 200mA
{
Change Q1 and R
S
for higher current
and/or different gain.
I
V
R
100mA/V as shown
OUT
IN
S
==
Figure 5. Voltage-Controlled Current Sink
V+
0V
4
100k
R4
100k
R3
100k
V
OUT
V+
1
⁄
2
MIC7122
C1
0.001µF
R2
100k
V+
Figure 6. Square Wave Oscillator
R3
330k
R1
33k
0V
R2
330k
R4
330k
C1
1µF
V
OUT
V+
1
⁄2 MIC7122
IN
V+
C
OUT
R
L
A
R2
R1
330k
33k
10
V
=− = =−
Figure 7. AC-Coupled Inverting Amplifier
