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参数资料
| 型号： | KIT33972AEWEVBE |
| 厂商： | Freescale Semiconductor |
| 文件页数： | 15/32页 |
| 文件大小： | 0K |
| 描述： | KIT EVALUATION FOR MC33972 |
| 标准包装： | 1 |
| 主要目的： | 接口，开关探测 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | MC33972 |
| 主要属性： | 8 可编程输入（电池开关或接地开关） |
| 次要属性： | 14 开关至接地输入 |
| 已供物品： | 板，CD |
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Analog Integrated Circuit Device Data
22
Freescale Semiconductor
33972
TYPICAL APPLICATIONS
INTRODUCTION
Figure 14. Analog Ratiometric Conversion
To read a potentiometer sensor, the wiper should be
grounded and brought back to the module ground, as
illustrated in Figure 14. With the wiper changing the
impedance of the sensor, the analog voltage on the input will
represent the position of the sensor.
Using the Analog feature to provide 2.0 mA of pull-up
current to an analog sensor may induce error due to the
accuracy of the current source. For this reason, a ratiometric
conversion must be considered. Using two current sources
(one for the sensor and one to set the reference voltage to the
A/D converter) will yield a maximum error (owing to the
33972) of 4%.
Higher accuracy may be achieved through module level
calibration. In this example, we use the resistor values from
Figure 14 and assume the current sources are 4% from each
other. The user may use the module end-of-line tester to
calculate the error in the A/D conversion. By placing a
2.0 k
Ω, 0.1% resistor in the end-of-line test equipment and
assuming a perfect 2.0 mA current source from the 33972, a
calculated A/D conversion may be obtained. Using the
equation yields the following:
The ADC value of 213 counts is the value with 0% error
(neglecting the resistor tolerance and AMUX input offset
voltage). Now we can calculate the count value induced by
the mismatch in current sources. From a sample device the
maximum current source was measured at 2.05 mA and
minimum current source was measured at 1.99 mA. This
yields 3% error in A/D conversion. The A/D measurement
will be as follows:
This A/D conversion is 3% low in value. The error
correction factor of 1.03 may be used to correct the value:
An error correction factor may then be stored in E2
memory and used in the A/D calculation for the specific input.
Each input used as analog measurement will have a
dedicated calibrated error correction factor.
POWER MOSFET/LED DRIVER AND MONITOR
Because of the flexible programming of the 33972 device,
it may be used to drive small loads like LEDs or MOSFET
gates. It was specifically designed to power up in the Normal
mode with the inputs tri-state. This was done to ensure the
LEDs or MOSFETs connected to the 33972 power up in the
off-state. The switch programmable inputs (SP0–SP7) have
a source-and-sink capability, providing effective MOSFET
gate control. To complete the circuit, a pull-down resistor
should be used to keep the gate from floating during the
where the SG0 input is used to monitor the drain-to-source
voltage of the external MOSFET. The 1.5 k
Ω resistor is used
to set the drain-to-source trip voltage. With the 2.0 mA
current source enabled, an interrupt will be generated when
the drain-to-source voltage is approximately 1.0 V.
VDD
VPWR
VDD
SI
SO
SCLK
INT
CS
AMUX
MOSI
MISO
AN0
VBAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
WAKE
VBAT
SCLK
CS
INT
16
2.0
VPWR
2.0mA
2.39k
Ω
0.1%
4.54V to 5.02V
Analog
Ports
VREF(H)
VREF(L)
Analog Sensor
or Analog Switch
R2
I2
I1
R1
VPWR
mA
2.0
VPWR
mA
16
mA
33972
MCU
ADC =
I1 x R1
I2 x R2
x 255
ADC =
2.0mA x 2.0k
Ω
x 255
2.0mA x 2.39k
Ω
ADC = 213 counts
ADC =
1.99mA x 2.0k
Ω
x255
2.05mA x 2.39k
Ω
ADC = 207 counts
ADC = 207 counts x 1.03
ADC = 213 counts
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