MCP3202-CI/P Microchip Technology Inc., MCP3202-CI/P Datasheet - Page 16

• Manufacturer Part Number: MCP3202-CI/P
• Description: A/D Converter, 2.7V, 12-Bit, SPI I'face, 2-Ch., DIP-8
• Manufacturer: Microchip Technology Inc.

Specifications of MCP3202-CI/P

• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

MCP3202
6.2
When the MCP3202 initiates the sample period, charge
is stored on the sample capacitor. When the sample
period is complete, the device converts one bit for each
clock that is received. It is important for the user to note
that a slow clock rate will allow charge to bleed off the
sample cap while the conversion is taking place. At
85°C (worst case condition), the part will maintain
proper charge on the sample capacitor for at least
1.2 ms after the sample period has ended. This means
that the time between the end of the sample period and
the time that all 12 data bits have been clocked out
must not exceed 1.2 ms (effective clock frequency of
10 kHz). Failure to meet this criteria may induce linear-
ity errors into the conversion outside the rated specifi-
cations. It should be noted that during the entire
conversion cycle, the A/D Converter does not require a
constant clock speed or duty cycle, as long as all timing
specifications are met.
6.3
If the signal source for the A/D Converter is not a low
impedance source, it will have to be buffered or inaccu-
rate conversion results may occur. It is also recom-
mended that a filter be used to eliminate any signals
that may be aliased back into the conversion results.
This is illustrated in Figure 6-3 below where an op amp
is used to drive the analog input of the MCP3202. This
amplifier provides a low impedance output for the con-
verter input and a low pass filter, which eliminates
unwanted high frequency noise.
Low pass (anti-aliasing) filters can be designed using
Microchip’s interactive FilterLab
will calculate capacitor and resistor values, as well as,
determine the number of poles that are required for the
application. For more information on filtering signals,
see the application note AN699 “Anti-Aliasing Analog
Filters for Data Acquisition Systems.
”
FIGURE 6-3:
used to implement a 2nd order anti-aliasing filter for
the signal being converted by the MCP3202.
DS21034D-page 16
V
IN
R
1
Maintaining Minimum Clock Speed
Buffering/Filtering the Analog Inputs
C
C
R
2
1
2
The MCP601 Operational Amplifier is
R
MCP601
3
+
-
R
4
IN-
™
IN+
software. FilterLab
MCP3202
V
DD
0.1 F
10 F
6.4
When laying out a printed circuit board for use with
analog components, care should be taken to reduce
noise wherever possible. A bypass capacitor should
always be used with this device and should be placed
as close as possible to the device pin. A bypass capac-
itor value of 0.1 µF is recommended.
Digital and analog traces should be separated as much
as possible on the board and no traces should run
underneath the device or the bypass capacitor. Extra
precautions should be taken to keep traces with high
frequency signals (such as clock lines) as far as possi-
ble from analog traces.
Use of an analog ground plane is recommended in
order to keep the ground potential the same for all
devices on the board. Providing V
devices in a “star” configuration can also reduce noise
by eliminating current return paths and associated
errors. See Figure 6-4. For more information on layout
tips when using A/D Converters, refer to AN688 “Lay-
out Tips for 12-Bit A/D Converter Applications”
(DS00688).
FIGURE 6-4:
configuration in order to reduce errors caused by
current return paths.
Layout Considerations
Device 1
V
DD
Device 2
Connection
traces arranged in a ‘Star’
© 2006 Microchip Technology Inc.
V
DD
Device 3
DD
Device 4
connections to