User manual
Active Filter Demo Board Kit User’s Guide
DS51614A-page 10 © 2006 Microchip Technology Inc.
The user provides the supply voltages, which need to be in the allowed range for the
installed op amps. Any of Microchip’s op amps that operate below 5.5V can be used;
higher voltage parts can be accommodated (see Section 4.2 “Power Supplies”). Five
MCP6271 op amps are included in the accessory bag for convenience.
The power lines are bypassed by 1.0 µF capacitors at each board input. The op amps
also have 0.1 µF local bypass capacitors.
2.4 V
DD
/2 FILTER SECTION SET-UP
Figure 2-2 gives the circuit diagram for the V
DD
/2 Filter Section. It allows the mid-supply
voltage (V
DD
/2) to be set by an external power supply (JP
1
at EXT), or internally (JP
1
at INT) by the on-board op amp (U
1
). The headers and test points allow the user
flexibility in setting up a filter circuit.
FIGURE 2-2: V
DD
/2 Filter Section Circuit.
The V
DD
/2 Filter Section PCB is shown in Figure 2-3. The single op amp U1 can have
either a PDIP-8 or SOIC-8 package:
• PDIP-8 packages are inserted into the DIP-8 socket above the U1 label
• SOIC-8 packages can be accommodated; see Section 4.6 “Using 8-Pin SOIC
Op Amps”
• Only one op amp can be connected at a time
Select the mid-supply power source by setting jumper JP1 to (see Figure 2-3):
• Internal V
DD
/2 (INT on bottom)
- Op amp U1 drives the V
DD
/2 line on all of the PCBs
-The V
DD
/2 line must be disconnected from any power supply (at P1 or TP4)
• External V
DD
/2 (EXT on top, as shown)
- Op amp U1 has no load
-The V
DD
/2 line must be connected to an external supply voltage (at P1 or
TP4)
The headers P1 and J1 on the left of the board are unpopulated (see Figure 2-3):
• The test points TP1 through TP5 provide connections for the same voltages
• P1 and J1 can be populated by the user, if desired, to connect to another (user
provided) board on the left
GND
V
IN
GND
P
1
GND
V
DD
/2
V
DD
C
1
1.0 µF
J
1
V
DD
V
DD
/2
GND
P
2
GND
V
OUT
GND
J
2
C
2
1.0 µF
TP
3
JP
1
EXT
INT
C
4
0.1 µF
V
DD
R
2
R
1
TP
1
TP
2
GND
V
IN
TP
4
V
DD
/2
TP
5
GND
MCP6271
U
1
C
3
20 kΩ
20 kΩ
0.1 µF
TP
5