Datasheet
MCP660/1/2/3/4/5/9
DS22194D-page 26 2009-2012 Microchip Technology Inc.
4.8 Typical Applications
4.8.1 50 LINE DRIVER
Figure 4-10 shows the MCP661 driving a 50 line. The
large output current (e.g., see Figure 2-18) makes it
possible to drive a back-matched line (R
M2
, the 50
line and the 50 load at the far end) to more than ±2V
(the load at the far end sees ±1V). It is worth mention-
ing that the 50 line and the 50 load at the far end
together can be modeled as a simple 50 resistor to
ground.
FIGURE 4-10: 50
Line Driver.
The output headroom limits would be V
OL
= -2.3V and
V
OH
= +2.3V (see Figure 2-16), leaving some design
room for the ±2V signal. The open-loop gain (A
OL
)
typically does not decrease significantly with a 100
load (see Figure 2-11). The maximum power dissipated
is about 48 mW (see Section 4.2.3 “Power
Dissipation”), so the temperature rise (for the
MCP661 in the SOIC-8 package) is under 8°C.
4.8.2 OPTICAL DETECTOR AMPLIFIER
Figure 4-11 shows a transimpedance amplifier, using
the MCP661 op amp, in a photo detector circuit. The
photo detector is a capacitive current source. R
F
pro-
vides enough gain to produce 10 mV at V
OUT
. C
F
stabi-
lizes the gain and limits the transimpedance bandwidth
to about 1.1 MHz. The parasitic capacitance of R
F
(e.g.,
0.2 pF for a 0805 SMD) acts in parallel with C
F
.
FIGURE 4-11: Transimpedance Amplifier
for an Optical Detector.
4.8.3 H-BRIDGE DRIVER
Figure 4-12 shows the MCP662 dual op amp used as
an H-bridge driver. The load could be a speaker or a
DC motor.
FIGURE 4-12: H-Bridge Driver.
This circuit automatically makes the noise gains (G
N
)
equal, when the gains are set properly, so that the fre-
quency responses match well (in magnitude and in
phase). Equation 4-7 shows how to calculate R
GT
and
R
GB
so that both op amps have the same DC gains;
G
DM
needs to be selected first.
EQUATION 4-7:
Equation 4-8 gives the resulting Common mode and
Differential mode output voltages.
EQUATION 4-8:
R
F
301
R
G
301
R
M1
49.9
50
R
M2
49.9
50
Line
+2.5V
-2.5V
MCP66X
Photo
Detector
C
D
C
F
R
F
V
DD
/2
30pF
100 k
1.5 pF
I
D
100 nA
V
OUT
MCP661
R
F
R
F
V
IN
V
OT
R
F
R
GB
V
OB
V
DD
/2
R
GT
R
L
½ MCP662
½ MCP662
G
DM
V
OT
V
OB
–
V
IN
V
DD
2
–
--------------------------------- 1 V/V
R
GT
R
F
G
DM
2
1–
---------------------------------=
R
GB
R
F
G
DM
2
-------------------=
V
OT
V+
OB
2
---------------------------
V
DD
2
-----------=
V
OT
V–
OB
G
DM
V
IN
V
DD
2
-----------–
=