MCP6022-I/SL Microchip Technology, MCP6022-I/SL Datasheet - Page 14

• Manufacturer Part Number: MCP6022-I/SL
• Description: Rail-to-Rail Input/Output, 10 MHz Op Amps
• Manufacturer: Microchip Technology

MCP6021/2/3/4
1.
2.
3.8
Due to their speed capabilities, a little extra care in the
PCB (Printed Circuit Board) layout can make a
significant difference in the performance of these op
amps. Good PC board layout techniques will help you
achieve the performance shown in the Electrical
Characteristics and Typical Performance Curves, while
also helping you minimize EMC (Electro-Magnetic
Compatibility) issues.
Use a solid ground plane and 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. Separating
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 the guard
trace 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.
DS21685B-page 14
Inverting (Figure 3-7) and Transimpedance
Gain Amplifiers (convert current to voltage, such
as photo detectors).
a.
b.
Non-inverting Gain and Unity-Gain Buffer
a.
b.
Connect the guard ring to the non-inverting
input pin (V
to the same reference voltage as the op
amp’s input (e.g., V
Connect the inverting pin (V
with a wire that does not touch the PCB
surface.
Connect the guard ring to the inverting input
pin (V
common mode input voltage.
Connect the non-inverting pin (V
input with a wire that does not touch the
PCB surface.
High-Speed PCB Layout
IN
–); this biases the guard ring to the
IN
+). This biases the guard ring
DD
/2 or ground).
IN
–) to the input
IN
+) to the
3.9
3.9.1
Figure 3-8 shows a third-order Butterworth filter that
can be used as an A/D converter driver. It has a band-
width of 20 kHz and a reasonable step response. It will
work well for conversion rates of 80 ksps and greater (it
has 29 dB attenuation at 60 kHz).
FIGURE 3-8:
anti-aliasing filter with a 20 kHz cutoff frequency.
This filter can easily be adjusted to another bandwidth
by multiplying all capacitors by the same factor.
Alternatively, the resistors can all be scaled by another
common factor to adjust the bandwidth.
3.9.2
Figure 3-9 shows the MCP6021 op amp used as a
transimpedance amplifier in a photo detector circuit.
The photo detector looks like a capacitive current
source, so the 100 k resistor gains the input signal to
a reasonable level. The 5.6 pF capacitor stabilizes this
circuit and produces a flat frequency response with a
bandwidth of 370 kHz.
FIGURE 3-9:
for an optical detector.
8.45 k
1.2 nF
Typical Applications
A/D CONVERTER DRIVER AND
ANTI-ALIASING FILTER
OPTICAL DETECTOR AMPLIFIER
Detector
Photo
14.7 k
100 pF
A/D converter driver and
Transimpedance amplifier
33.2 k
100 pF
2003 Microchip Technology Inc.
1.0 nF
V
DD
/2
100 k
5.6 pF
MCP6021
MCP602X