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| 型号： | KIT33975AEWEVBE |
| 厂商： | Freescale Semiconductor |
| 文件页数： | 16/32页 |
| 文件大小： | 0K |
| 描述： | KIT EVALUATION FOR MC33975 |
| 标准包装： | 1 |
| 主要目的： | 接口，开关探测 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | MC33975 |
| 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
Freescale Semiconductor
23
33975
TYPICAL APPLICATIONS
OPERATIONAL MODES
TYPICAL APPLICATIONS
The 33975’s primary function is the detection of open or
closed switch contacts. However, there are many features
that allow the device to be used in a variety of applications.
The following is a list of applications to consider for the IC:
Sensor power supply
Switch monitor for metallic or elastomeric switches
Analog sensor inputs (Ratiometric)
Power MOSFET/LED driver and monitor
Multiple 33975 devices in a module system
The following paragraphs describe the applications in detail.
SENSOR POWER SUPPLY
Each input may be used to supply current to sensors external
to a module. Many sensors such as Hall effect, pressure
sensors, and temperature sensors require a supply voltage to
power the sensor, and provide an open collector or analog
output. Figure 13 shows how the 33975 may be used to
supply power and interface to these types of sensors. In an
application where the input makes continuous transitions,
consider using the wake-up/interrupt command to disable
the interrupt for the particular input.
Figure 13. Sensor Power Supply
METALLIC/ELASTOMERIC SWITCH
Metallic switch contacts often develop higher contact
resistance over time owing to contact corrosion. The
corrosion is induced by humidity, salt, and other elements
that exist in the environment. For this reason the 33975
provides two settings for contacts. When programmed for
metallic switches, the device provides higher wetting current
to keep switch contacts free of oxides. The higher current
occurs for the first 20 ms of switch closure. Where longer
duration of wetting current is desired, the user may send the
wetting current timer command and disable the timer. Wetting
current will be continuous to the closed switch. After the time
period set by the MCU, the wetting current timer command
may be sent again to enable the timer. The user must
consider power dissipation on the device when disabling the
timer. (Refer to the paragraph entitled Temperature Monitor,
page 22.)
To increase the amount of wetting current for a switch
contact, the user has two options. Higher wetting current to a
switch may be achieved by paralleling SGn or SPn inputs.
This will increase wetting current by 32 mA for each input
added to the switch-to-ground contact and 16 mA for switch-
to-battery contacts. The second option is to simply add an
external resistor pull-up to the VPWR supply for switch-to-
ground inputs or a resistor to ground for a switch-to-battery
input. Adding an external resistor has no effect on the
operation of the device.
Elastomeric switch contacts are made of carbon and have a
high contact resistance. Resistance of 1.0 k
is common. In
applications with elastomeric switches, the pull-up and pull-
down currents must be reduced to prevent excessive power
dissipation at the contact. Programming for a lower current
settings is provided in the Functional Device Operation
Command.
ANALOG SENSOR INPUTS (RATIOMETRIC)
The 33975 features a 22-to-1 analog multiplexer. Setting the
binary code for a specific input in the analog command allows
the microcontroller to perform analog to digital conversion on
any of the 22 inputs. On rising edge of the CS, the multiplexer
connects a requested input to the AMUX pin. The AMUX pin
is clamped to max of VDD volts regardless of the higher
voltages present on the input pin. After an input has been
selected as the analog, the corresponding bit in the next SO
data stream will be logic [0].
The input pin, when selected as analog, may be configured
as analog with high-impedance, analog with 4.0 mA pull-up,
the 33975 may be used to provide a ratiometric reading of
variable resistive input.
VDD
VPWR
VDD
SI
SO
SCLK
INT
CS
MOSI
MISO
VBAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
WAKE
33975
SCLK
CS
INT
MCU
32
4.0
VPWR VPWR
32 mA
IOC[7:0]
X
Reg
Input Capture
Timer Port
Hall-Effect
Sensor
mA
32
4.0
VPWR VPWR
mA
VBAT
mA
AMUX
0V
VPWR
SG13
0V
VDD
AMUX
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