MCP631_14 Datasheet, PDF (24/60 Pages) Microchip Technology – Unity-Gain Stable

MCP631/2/3/4/5/9
4.6 High-Speed PCB Layout
These op amps are fast enough that a little extra care
in the printed circuit board (PCB) layout can make a
significant difference in performance. Good PCB layout
techniques will help achieve the performance shown in
the specifications and typical performance curves; it
will also help minimize electromagnetic compatibility
(EMC) issues.
Use a solid ground plane. Connect the bypass local
capacitor(s) to this plane with minimal length traces.
This cuts down inductive and capacitive crosstalk.
Separate digital from analog, low-speed from
high-speed, and low-power from high-power. This will
reduce interference.
Keep sensitive traces short and straight. Separate
them from interfering components and traces. This is
especially important for high-frequency (low rise time)
signals.
Sometimes, it helps to place guard traces next to victim
traces. They should be on both sides of the victim trace
and as close as possible. Connect guard traces to
ground plane at both ends and in the middle for long
traces.
Use coax cables, or low-inductance wiring, to route
signal and power to and from the PCB. Mutual and
self-inductance of power wires is often a cause of
crosstalk and unusual behavior.
4.7 Typical Applications
4.7.1 POWER DRIVER WITH HIGH GAIN
Figure 4-10 shows a power driver with high gain
(1 + R₂/R₁). The short-circuit current of the
MCP631/2/3/4/5/9 op amps makes it possible to drive
significant loads. The calibrated input offset voltage
supports accurate response at high gains. R₃ should
be small and equal to R₁||R₂ in order to minimize the
bias current induced offset.
R₁
V_DD/2
R₃
V_IN
FIGURE 4-10:
R₂
-
+ MCP63X
Power Driver.
V_OUT
R_L
4.7.2 OPTICAL DETECTOR AMPLIFIER
Figure 4-11 shows a transimpedance amplifier, using
the MCP63X op amp, in a photo detector circuit. The
photo detector is a capacitive current source. R_F
provides enough gain to produce 10 mV at V_OUT. C_F
stabilizes 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.
C_F
1.5 pF
Photo
Detector
I_D
100 nA
C_D
30 pF
R_F
100 k
-
V_OUT
+ _MCP632
V_DD/2
FIGURE 4-11:
Transimpedance Amplifier
for an Optical Detector.
4.7.3 H-BRIDGE DRIVER
Figure 4-12 shows the MCP632 dual op amp used as
a H-bridge driver. The load could be a speaker or a DC
motor.
V_IN
½ MCP633
+
-
R_F
R_F
V_OT
R_GT
R_GB
R_F
-
R_L
V_OB
V_DD/2
+ _{½ MCP633}
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
frequency 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.
DS20002197C-page 24
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