MC33972A FREESCALE [Freescale Semiconductor, Inc], MC33972A Datasheet - Page 20

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

Table 19. Interrupt Timer
switch reads in Sleep Mode. The period is set in the sleep
command and may be set to 000 (no period) to 111 (64ms).
In Sleep Mode when the scan timer expires, inputs will
behave as programmed prior to sleep command. The 33972
will wake up for approximately 125μs and read the switch
inputs. At the end of the 125μs, the input switch states are
compared with the switch state prior to sleep command.
When switch state changes are detected, an interrupt is
generated (when enabled; refer to wake-up / interrupt
command description on page 15), and the device enters
Normal Mode. Without switch state changes, the 33972 will
reset the scan timer, inputs become tri-state, and the Sleep
Mode continues until the scan timer expires again.
timer.
Table 20. Scan Timer
Normal Mode.
20
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The scan timer sets the polling period between input
Table 20
Note The interrupt and scan timers are disabled in the
Bits 543
Bits 210
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
shows the programmable settings of the Scan
No interrupt wake-up
Interrupt Period
Scan Period
No Scan
128ms
256ms
512ms
1.024s
2.048s
1.0ms
2.0ms
4.0ms
8.0ms
32ms
64ms
16ms
32ms
64ms
33972 device exits Sleep Mode and enters Normal Mode.
Notice that the device will exit Sleep Mode when the interrupt
timer expires or when a switch change of state occurs. The
falling edge of INT triggers the MCU to wake from Sleep
state.
Sleep Mode. During the 125μs, the device is fully active and
switch states are read. The quiescent current is calculated by
integrating the normal running current over scan period plus
approximately 60μA.
TEMPERATURE MONITOR
programmed with the wetting current timers disabled,
considerable power will be dissipated by the IC. For this
reason, temperature monitoring has been implemented. The
temperature monitor is active in the Normal Mode only. When
the IC temperature is above the thermal limit, the temperature
monitor will do all of the following:
edge of
the thermal limit. When die temperature has cooled below
thermal limit, the device will resume previously programmed
settings.
Figure
With multiple switch inputs closed and the device
• Generate an interrupt.
• Force all 16mA pull-up and pull-down current sources to
• Maintain the 2.0mA current source and all other
• Set the thermal flag bit in the SPI output register.
The thermal flag bit in the SPI word will be cleared on rising
revert to 2.0mA current sources.
functionality.
Figure 12
CS
Inputs active for 125 us
Inputs active for 125 us
Inputs active for 125 us
out of 32 ms
out of 32 ms
out of 32 ms
5, page 9, is a graphical description of how the
Inputs active for
125μs out of 32ms
Figure 12. Sleep Current Waveform
provided the die temperature has cooled below
illustrates the current consumed during
I = V/R or 0.270V/100Ω = 2.7mA
I=V/R or 0.270V/100ohm = 2.7mA
I=V/R or 0.270V/100ohm = 2.7mA
I=V/R or 0.270V/100ohm = 2.7mA
Analog Integrated Circuit Device Data
6.0mV/100Ω = 60μA
I = V/R or
I=V/R or 6mV/100ohm = 60 uA
I=V/R or 6mV/100ohm = 60 uA
I=V/R or 6mV/100ohm = 60 uA
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