33975 datasheet(23/34 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33975

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Figure 5, page 11, 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 12 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.

Figure 12. 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:

• Generate an interrupt.

• Force all wetting current sources to revert to 2.0mA/

4.0mA sustain currents

• Maintain the 2.0mA/4.0mA 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 the

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.

Inputs active for 125 us

out of 32 ms

I=V/R or 0.270V/100ohm = 2.7mA

I=V/R or 6mV/100ohm = 60 uA

Inputs active for 125 us

out of 32 ms

I=V/R or 0.270V/100ohm = 2.7mA

I=V/R or 6mV/100ohm = 60 uA

Inputs active for 125 us

out of 32 ms

I=V/R or 0.270V/100ohm = 2.7mA

I=V/R or 6mV/100ohm = 60 uA

I=V/R or 0.270V/100

Ω=2.7mA

Inputs active for

125

μs out of 32ms

I=V/R or

6.0mV/100

Ω=60μA

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