MC33993DWB View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

MC33993DWB

MULTIPLE SWITCH DETECTION INTERFACE

Motorola => Freescale 

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 15 shows the programmable settings of the Scan

timer.

Table 15. 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

110

32 ms

111

64 ms

Note The interrupt and scan timers are disabled in the

Normal mode.

Figure 3, 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 9 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.

II==VV//RRoor r0.027.207V0/1V00/o1h0m0=Ω2=.72m.7A mA

InInpuptus atsctiavcetfiovre12fo5 rus

ou1t2o5f µ32smosut of 32 ms

II=V/RRoorr6mV/100ohm = 60 uA

6.0 mV/100 Ω=60 µA

Figure 9. 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 16 mA pull-up and pull-down current sources to

revert to 2.0 mA current sources.

• Maintain the 2.0 mA current source 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.

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

33993/D

19

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