MCP3021 Microchip Technology, Inc., MCP3021 Datasheet - Page 19

• Manufacturer Part Number: MCP3021
• Description: The Microchip Technology Inc
• Manufacturer: Microchip Technology, Inc.

6.3
In some instances, it may be necessary to test for
MCP3021 presence on the I
a conversion, described in Figure 6-4. Here we are set-
ting the R/W bit in the address byte to a zero. The
MCP3021 will then acknowledge by pulling SDA low
during the ACK clock and then release the bus back to
the I
issued from the master and I
continue.
FIGURE 6-4:
6.4
6.4.1
V
erence voltage. A bypass capacitor value of 0.1 µF is
recommended. Adding a 10 µF capacitor in parallel is
recommended to attenuate higher frequency noise
present in some systems.
FIGURE 6-5:
6.4.2
When laying out a printed circuit board for use with
analog components, care should be taken to reduce
noise wherever possible. A bypass capacitor from
to ground should always be used with this device and
should be placed as close as possible to the device pin.
A bypass capacitor value of 0.1 µF is recommended.
Digital and analog traces should be separated as much
as possible on the board, with no traces running
underneath the device or the bypass capacitor. Extra
10 µF
DD
2003 Microchip Technology Inc.
SDA
SCL
2
supplies the power to the device as well as the ref-
C master. A stop or repeated start bit can then be
Device Polling
Device Power and Layout
Considerations
Start
A
Bit
0.1 µF
IN
POWERING THE MCP3021
LAYOUT CONSIDERATIONS
1
1
Device bits
MCP3021
2
0
V
DD
3
0
Device Polling.
Powering the
V
Address Byte
DD
4
1 A2 A1 A0 0
Address bits
5
2
SDA
SCL
C bus without performing
2
6
C communication can
R
7
MCP3021 response
PU
R/W
8
V
MCP3021
CC
To
Microcontroller
9
R
PU
Start
Bit
.
V
DD
precautions should be taken to keep traces with high
frequency signals (such as clock lines) as far as
possible from analog traces.
The MCP3021 should be connected entirely to the ana-
log ground place, as well as the analog power trace.
The pull-up resistors can be placed close to the
microcontroller and tied to the digital power or V
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 (Figure 6-6). For more information on layout tips
when using the MCP3021 or other ADC devices, refer
to AN688, “Layout Tips for 12-Bit A/D Converter
Applications”.
FIGURE 6-6:
‘Star’ configuration in order to reduce errors
caused by current return paths.
6.4.3
The MCP3021 uses V
ence. In some applications, it may be necessary to use
a stable reference to achieve the required accuracy.
Figure 6-7 shows an example using the MCP1541 as a
4.096V 2% reference.
FIGURE 6-7:
Reference Configuration.
0.1 µF
Device 1
Reference
MCP1541
USING A REFERENCE FOR
SUPPLY
4.096V
V
DD
Device 2
C
Connection
DD
V
Stable Power and
L
1 µF
A
DD
IN
as power and also as a refer-
V
DD
traces arranged in a
MCP3021
MCP3021
Device 3
V
DD
SDA
SCL
DS21805A-page 19
DD
Device 4
connections to
R
PU
V
CC
CC
.