June 2005
7
MIC7122
Micrel
capacitance C
IN. The value of CFB is determined by first
estimating C
IN and then applying the following formula:
R
IN × CIN ≤ RFB × CFB
VIN
CFB
RFB
VOUT
CIN
RIN
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
VOUT
0V to V+
V+
VIN
12 MIC7122
0V to
V+
AV
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
VOUT
0V to V+
V+
VIN
0V to V+
12 MIC7122
VOUT = VIN
Figure 4. Voltage Follower/Buffer
VOUT
0V to V+
V+
VIN
0V to 2V
12 MIC7122
RS
10
12W
Load
VS
0.5V to Q1 VCEO(sus)
IOUT
Q1
2N3904
VCEO = 40V
IC(max) = 200mA
{
Change Q1 and RS
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
R4
100k
R4
100k
R3
100k
VOUT
V+
12 MIC7122
C1
0.001F
R2
100k
V+
Figure 6. Square Wave Oscillator
R3
330k
R1
33k
0V
R2
330k
R4
330k
C1
1F
VOUT
V+
12 MIC7122
CIN
V+
COUT
RL
A
R2
R1
330k
33k
10
V =
=
=
Figure 7. AC-Coupled Inverting Amplifier