MC33972EW/R2 FREESCALE [Freescale Semiconductor, Inc], MC33972EW/R2 Datasheet - Page 22

• Manufacturer Part Number: MC33972EW/R2
• Description: Multiple Switch Detection Interface with Suppressed Wake-up
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

grounded and brought back to the module ground, as
illustrated in
impedance of the sensor, the analog voltage on the input will
represent the position of the sensor.
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%.
calibration. In this example, we use the resistor values from
Figure 14
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 kΩ, 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:
22
33972
TYPICAL APPLICATIONS
INTRODUCTION
To read a potentiometer sensor, the wiper should be
Using the Analog feature to provide 2.0 mA of pull-up
Higher accuracy may be achieved through module level
V
Analog Sensor
or Analog Switch
V
BAT
BAT
R
2.0mA
1
I
1
Figure 14. Analog Ratiometric Conversion
and assume the current sources are 4% from each
SG13
SG12
Figure
SP0
SG0
SG1
SP1
SP7
2.0mA
I
2
16
mA
16
mA
2.39kΩ
0.1%
V
V
14. With the wiper changing the
PWR
PWR
33972
V
4.54V to 5.02V
V
PWR
PWR
2.0
mA
2.0
mA
R
2
WAKE
AMUX
VPWR
SCLK
VDD
INT
CS
SO
SI
V
DD
MOSI
SCLK
CS
MISO
INT
V
V
AN0
Analog
REF(H)
REF(L)
MCU
Ports
(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:
correction factor of 1.03 may be used to correct the value:
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
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
Sleep modes.
where the SG0 input is used to monitor the drain-to-source
voltage of the external MOSFET. The 1.5 kΩ 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.
The ADC value of 213 counts is the value with 0% error
This A / D conversion is 3% low in value. The error
An error correction factor may then be stored in E
Because of the flexible programming of the 33972 device,
ADC =
Figure
ADC =
ADC = 207 counts x 1.03
ADC =
2.05mA x 2.39kΩ
ADC = 213 counts
ADC = 213 counts
15, page 23, shows an application
1.99mA x 2.0kΩ
ADC = 207 counts
2.0mA x 2.39kΩ
Analog Integrated Circuit Device Data
2.0mA x 2.0kΩ
I1 x R1
I2 x R2
Freescale Semiconductor
x 255
x 255
x 255
2