33975 Datasheet, PDF (21/32 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface with Suppressed Wake-Up and 32mA Wetting Current

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Figure 5, page 10, is a graphical description of how the
33975 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
In^Inpu^pt^us a^tscti^av^ce^tfⁱo^vr^e12^fo5 ^rus
ou¹t²o⁵f ^µ32^sm^os^{ut of 32 ms}
II=V/RRoorr6mV/100ohm = 60 uA
6.0 mV/100 Ω=60 µA
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:
• Generate an interrupt.
• Force all wetting current sources to revert to 2.0 mA/
4.0 mA sustain currents
• Maintain the 2.0 mA/4.0 mA sustain currents and all
other functionality.
• Set the thermal flag bit in the SPI output register.
The thermal flag bit in the SPI word will be cleared on rising
edge of CS provided the die temperature has cooled below
the thermal limit. When die temperature has cooled below
thermal limit, the device will resume previously programmed
settings.
Figure 11. Sleep Current Waveform
Analog Integrated Circuit Device Data
Freescale Semiconductor
33975
21