MC33993DWB View Datasheet(PDF) - Motorola => Freescale
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MC33993DWB Datasheet PDF : 28 Pages
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APPLICATIONS
Introduction
The 33993’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 33993 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 10 shows how the 33993 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.
VBAT
VBAT
16 mA
33993
SP0
SP1
VPWR
VDD
VDD
SP7
WAKE
SG0
SG1
VPWR VPWR
SI
SCLK
CS
16
mA
SG12
2.0 SO
mA INT
VPWR VPWR
Hall-Effect
Sensor
16
mA
2.0
mA
Reg
SG13
X
2.5 kΩ
2.5 kΩ
MCU
MOSI
SCLK
CS
MISO
INT
IOC[7:0]
Input Capture
Timer Port
Figure 10. 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 33993 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 19.)
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 16 mA for each input added to
the switch contact. 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 kΩ 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 Device Operation Section beginning
on page 12 under Table 3, Metallic Command.
Analog Sensor Inputs (Ratiometric)
The 33993 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 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 2.0 mA pull-up, or
analog with 16 mA pull-up. Figure 11, page 21, shows how the
33993 may be used to provide a ratiometric reading of variable
resistive input.
33993/D
20
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
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