MCP3302-XI/SL Microchip Technology, MCP3302-XI/SL Datasheet - Page 18

• Manufacturer Part Number: MCP3302-XI/SL
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface, -40C to +85C, 14-SOIC 150mil, TUBE
• Manufacturer: Microchip Technology

MCP3302/04
FIGURE 6-3:
6.2.1
When the MCP3302/04 initiates, 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. For
the MCP330X devices, the recommended minimum
clock speed during the conversion cycle (T
105 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
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 equal to 610 µV.
Although the ADC is not production tested with a 2.5V
reference as shown, linearity will not change more than
0.1 LSB. See
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
DS21697D-page 18
Legend
I
VA
C
LEAKAGE
SAMPLE
Biasing Solutions
R
C
R
CHx
SS
PIN
SS
R
VA
V
MAINTAINING MINIMUM CLOCK
SPEED
SS
S
T
Figure 2-2
CHx
=
=
=
=
=
=
=
=
=
signal source
source impedance
input channel pad
input pin capacitance
threshold voltage
leakage current at the pin
due to various junctions
sampling switch
sampling switch resistor
sample/hold capacitance
REF
Analog Input Model.
at V
A/D converter does not have
and
DD
7 pF
C
Figure 2-9
PIN
= 5V. A trade-off exists
V
DD
for DNL and
V
V
T
T
= 0.6V
CONV
= 0.6V
) is
I
±1 nA
LEAKAGE
bring down the high pass corner. The value of R will
need to be 1 kΩ, or less, since higher input impedances
require additional acquisition time. Using the RC values
in
Figure 2-12
acquisition time.
FIGURE 6-4:
circuit for bipolar operation.
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
impedance. This circuit is shown in
Figure
V
IN
6-4, we have a 100 Hz corner frequency. See
for relation between input impedance and
10 µF
SS
Sampling
Switch
C
1 kΩ
1 µF
R
R
S
= 1 kΩ
Pseudo-differential biasing
V
© 2007 Microchip Technology Inc.
IN+
IN-
OUT
MCP1525
V
MCP330X
V
SS
C
= DAC capacitance
= 25 pF
IN
0.1 µF
V
SAMPLE
REF
Figure
V
DD
0.1 µF
= 5V
6-5.