參數資料
型號: MCP3221
廠商: Microchip Technology Inc.
英文描述: 560KBITS BRAM 400000 SYSTEM GATES 404 I/ - NOT RECOMMENDED for NEW DESIGN
中文描述: 低功耗12位A / D轉換器具有I2C⑩接口
文件頁數: 18/27頁
文件大?。?/td> 520K
代理商: MCP3221
MCP3221
DS21732B-page 18
2003 Microchip Technology Inc.
6.0
APPLICATIONS INFORMATION
6.1
Driving the Analog Input
The MCP3221 has a single-ended analog input (AIN).
For proper conversion results, the voltage at the AIN
pin must be kept between
V
SS
and
V
DD
. If the converter
has no offset error, gain error, INL or DNL errors, and
the voltage level of AIN is equal to or less than
V
SS
+ 1/2 LSB, the resultant code will be
000h
. Addi-
tionally, if the voltage at AIN is equal to or greater than
V
DD
- 1.5 LSB, the output code will be
FFFh
.
The analog input model is shown in Figure 6-1. In this
diagram, the source impedance (R
SS
) adds to the inter-
nal sampling switch (R
S
) impedance, directly affecting
the time required to charge the capacitor (C
SAMPLE
).
Consequently, a larger source impedance increases
the offset error, gain error and integral linearity errors of
the conversion. Ideally, the impedance of the signal
source should be near zero. This is achievable with an
operational amplifier, such as the MCP6022, which has
a closed-loop output impedance of tens of ohms.
FIGURE 6-1:
Analog Input Model, AIN.
6.2
Connecting to the I
2
C Bus
The I
2
C bus is an open-collector bus, requiring pull-up
resistors connected to the SDA and SCL lines. This
configuration is shown in Figure 6-2.
FIGURE 6-2:
Bus.
Pull-up Resistors on I
2
C
The number of devices connected to the bus is limited
only by the maximum bus capacitance of 400 pF. A
possible configuration using multiple devices is shown
in Figure 6-3.
FIGURE 6-3:
Bus.
Multiple Devices on I
2
C
C
PIN
7 pF
V
A
R
SS
AIN
V
T
= 0.6V
V
T
= 0.6V
I
LEAKAGE
±1 nA
Sampling
Switch
SS
R
S
= 1 k
C
SAMPLE
= DAC capacitance
= 20 pF
V
SS
V
DD
Legend
VA
R
SS
AIN
C
PIN
V
T
=
=
=
=
=
=
signal source
source impedance
analog input pad
analog input pin capacitance
threshold voltage
leakage current at the pin
due to various junctions
sampling switch
sampling switch resistor
sample/hold capacitance
I
LEAKAGE
SS
R
S
=
=
=
C
SAMPLE
P
SDA
SCL
V
DD
R
PU
R
PU
R
PU
is typically: 10 k
for f
SCL
= 100 kHz
2 k
for f
SCL
= 400 kHz
MCP3221
Analog
Input
Signal
M
AIN
SDA SCL
PIC16F876
Microcontroller
MCP3221
12-bit ADC
TC74
Temperature
Sensor
24LC01
EEPROM
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