33993 Datasheet, PDF (18/28 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface

FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
Table 17. Sleep Command
Sleep Command
Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 1 1 0 0XXXXXXXXXX
Table 18. Interrupt Timer
Bits 543
Interrupt Period
000
32 ms
001
64 ms
010
128 ms
011
256 ms
100
512 ms
101
1.024 s
110
2.048 s
111
4.096 s
The scan timer sets the polling period between input
switch reads in Sleep mode. The period is set in the sleep
command and may be set to 000 (no period) to 111 (64 ms).
In Sleep mode when the scan timer expires, inputs will
behave as programmed prior to sleep command. The 33993
will wake up for approximately 125 µs and read the switch
inputs. At the end of the 125 µs, the input switch states are
compared with the switch state prior to sleep command.
When switch state changes are detected, an interrupt (when
enabled; refer to wake-up / interrupt command description on
page 13) is generated and the device enters Normal mode.
Without switch state changes, the 33993 will reset the scan
timer, inputs become tri-state, and the Sleep mode continues
until the scan timer expires again.
Table 19 shows the programmable settings of the Scan
timer.
Table 19. Scan Timer
Bits 210
Scan Period
000
No Scan
001
1.0 ms
010
2.0 ms
011
4.0 ms
100
8.0 ms
101
16 ms
Table 19. Scan Timer
Bits 210
Scan Period
110
32 ms
111
64 ms
Note The interrupt and scan timers are disabled in the
Normal mode.
Figure 5, page 8, is a graphical description of how the
33993 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. Figure 11 illustrates the current consumed during
Sleep mode. During the 125 µs, 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 60 µA.
I^I==^VV^//^RR^oo^r r^0.0²⁷.2⁰7^V0^/1V⁰⁰/^o1^h0^m0⁼Ω²=^.72^m.7^A mA
Ion^I_u1npt₂u^p_o5tf^us _µ3a^t₂^sc_stmi^aov^c_seutf_tio^vor^ef12^f3o5_2ru_ms _s
II=V/RRoorr6mV/100ohm = 60 uA
6.0 mV/100 Ω=60 µA
Figure 11. Sleep Current Waveform
TEMPERATURE MONITOR
With multiple switch inputs closed and the device
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:
33993
18
Analog Integrated Circuit Device Data
Freescale Semiconductor