MC33972A FREESCALE [Freescale Semiconductor, Inc], MC33972A Datasheet - Page 15

• Manufacturer Part Number: MC33972A
• Description: Multiple Switch Detection Interface with Suppressed Wake-Up
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Table 7. Wake-up / Interrupt Command
WETTING CURRENT REGISTER
and 2.0mA (see
set the switch contact current level
the metallic bit to logic [0] will set the switch wetting current to
2.0mA. Programming the metallic bit to logic [1] will set the
switch contact wetting current to 16mA. The MCU may
change or update the wetting current register via software at
any time in Normal Mode.
current during switch closure. The higher level of current is
designed to keep switch contacts from building up oxides that
form on the switch contact surface.
Table 8. Metallic Command
WETTING CURRENT TIMER REGISTER
starts when the specific switch input crosses the comparator
threshold (4.0V). When the 20ms timer expires, the contact
current is reduced from 16mA to 2.0mA. The wetting current
timer may be disabled for a specific input. When the timer is
disabled, 16mA of current will continue to flow through the
Table 9. Wetting Current Timer Enable Command
Analog Integrated Circuit Device Data
Freescale Semiconductor
23
23
23
0
0
0
0
0
0
The 33972 has two levels of switch contact current, 16mA
Wetting current is designed to provide higher levels of
Each switch input has a designated 20ms timer. The timer
Wetting Current Timer Commands
Wake-up /Interrupt Command
22
22
22
0
0
0
0
0
0
Metallic Command
21
21
21
0
0
0
0
0
0
Figure
20
20
20
0
0
0
0
0
0
19
19
19
0
0
0
0
0
1
11). The metallic command is used to
18
18
18
1
1
0
0
1
0
17
17
17
1
1
0
0
1
0
(Table
16
16
16
0
1
0
1
1
0
15
15
X
X
X
X
15
8). Programming
X
X
14
14
X
X
14
X
X
X
X
sg13 sg12 sg11 sg10 sg9
sg13 sg12 sg11 sg10 sg9
sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
13
13
X
X
13
X
12
12
X
X
12
X
11
11
X
X
11
X
closed switch contact. With multiple wetting current timers
disabled, power dissipation for the IC must be considered.
register via software at any time in Normal Mode. This allows
the MCU to control the amount of time wetting current is
applied to the switch contact. Programming the wetting
current timer bit to logic [0] will disable the wetting current
timer. Programming the wetting current timer bit to logic [1]
will enable the wetting current timer
10
10
X
The MCU may change or update the wetting current timer
X
10
X
Figure 11. Contact Wetting and Sustain Current
X
9
X
9
X
9
Command Bits
Command Bits
Command Bits
Switch Contact Voltage
sg8
sg8
X
8
8
X
8
X
20 ms Wetting Current Timer
sp7
sg7
sp7
sg7
sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
7
7
7
16 mA Switch Wetting Current
sp6
sg6
sp6
sg6
2.0 mA Switch Sustain Current
6
6
6
FUNCTIONAL DEVICE OPERATION
sp5
sg5
sp5
sg5
5
5
5
sp4
sg4
sp4
sg4
4
4
4
(Table
OPERATIONAL MODES
sp3
sg3
sp3
sg3
3
3
3
9).
sp2
sg2
sp2
sg2
2
2
2
sp1
sg1
sp1
sg1
1
1
1
33972
sp0
sg0
sp0
sg0
0
0
0
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