MCP3302-I/ST Microchip Technology, MCP3302-I/ST Datasheet - Page 16

• Manufacturer Part Number: MCP3302-I/ST
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: Microchip Technology

MCP3302/04
FIGURE 6-3:
Resistance (R
6.2.1
When the MCP3302/04 initiates, charge is stored on
the sample capacitor. When the sample period is com-
plete, 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 sam-
ple period has ended. This means that the time
between the end of the sample period and the time that
all 13 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 linearity errors into the
conversion outside the rated specifications. It should
be noted that during the entire conversion cycle, the
A/D converter does not have requirements for clock
speed or duty cycle, as long as all timing specifications
are met.
6.3
For pseudo-differential bipolar operation, the biasing
circuit shown in Figure 6-4 shows a single ended input
AC coupled to the converter. This configuration will give
a digital output range of -4096 to +4095. With the 2.5V
reference the LSB size is equal to 610 µV.
DS21697A-page 16
2.5
2.0
1.5
1.0
0.5
0.0
100
MAINTAINING MINIMUM CLOCK SPEED
Biasing Solutions
S
) to maintain ±1 LSB INL.
Maximum Clock Frequency vs. Source
Source Resistance (ohms)
1000
10000
100000
FIGURE 6-4:
bipolar operation.
Although the ADC is not production tested with a 2.5V
reference as shown, linearity will not change more than
0.1 LSB. See Figure 2-2 and 2-9 for DNL and INL
errors versus V
between the high pass corner and the acquisition time.
The value of C will need to be quite large in order to
bring down the high pass corner. The value of R will
need to be 1 k , or less, since higher input impedances
require additional acquisition time. Using the RC values
in Figure 6-4, we have a 100 Hz corner frequency. See
Figure 2-12 for relation between input impedance and
acquisition time.
Using an external operation amplifier on the input
allows for gain and also buffers the input signal from the
input to the ADC allowing for a higher source imped-
ance. This circuit is shown in Figure 6-5.
FIGURE 6-5:
also buffers the input from any high impedance
sources.
1 k
V
IN
V
IN
1 µF
10 µF
C
1 k
1 µF
10 k
MCP6021
Pseudo-differential biasing circuit for
Adding an amplifier allows for gain and
REF
1 M
-
+
1 µF
R
at V
V
OUT
IN+
IN-
MCP1525
DD
2001 Microchip Technology Inc.
V
IN+
IN-
MCP1525
OUT
= 5V. A trade-off exists
MCP330X
V
IN
0.1 µF
V
MCP330X
REF
V
0.1 µF
V
IN
V
DD
0.1 µF
REF
= 5V
V
DD
0.1 µF
= 5V