MC33975A 데이터 시트보기 (PDF) - Freescale Semiconductor

부품명

상세내역

제조사

MC33975A

Multiple Switch Detection Interface with Suppressed Wake-up and 32 mA Wetting Current

Freescale Semiconductor 

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

WAKE-UP/INTERRUPT REGISTER

The Wake-up/Interrupt Register defines the inputs that are

allowed to wake the 33975 from Sleep mode or set the INT

pin low in Normal mode. Programming the wake-up/interrupt

bit to logic [0] will disable the specific input from generating

an interrupt and will disable the specific input from waking the

IC in Sleep mode (refer to Table 7). Programming the wake-

up/interrupt bit to logic [1] will enable the specific input to

generate an interrupt with switch change of state and will

enable the specific input as wake-up. The MCU may change

or update the Wake-up/Interrupt Register via software at any

time in Normal mode.

Table 7. Wake-Up /Interrupt Command

Wake-up/Interrupt 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 0 0 1 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0

0 0 0 0 0 0 1 1 X X sg1 sg1 sg1 sg1 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0

3210

WETTING CURRENT REGISTER

The 33975 has two levels of switch-to-ground contact

current, 32 and 4.0 mA, and two levels of switch-to-battery

contact current, 16 and 2.0 mA (see Figure 11). The metallic

command is used to set the switch contact current level (refer

to Table 8). Programming the metallic bit to logic [0] will set

the switch wetting current to 2.0 mA/4.0 mA. Programming

the metallic bit to logic [1] will set the switch contact wetting

current to 16 mA/32 mA. The MCU may change or update the

Wetting Current Register via software at any time in Normal

Mode.

Wetting current is designed to provide higher levels of current

during switch closure. The higher level of current is designed

to keep switch contacts from building up oxides that form on

the switch contact surface.

Switch Contact Voltage

32 mA Switch Wetting Current

4.0 mA Switch Sustain Current

20 ms Wetting Current Timer

Figure 11. Contact Wetting and Sustain Current

for Switch-to-Ground Input

Table 8. Metallic Command

Metallic 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 0 1 0 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0

0 0 0 0 0 1 0 1 X X sg1 sg1 sg1 sg1 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0

3210

WETTING CURRENT TIMER REGISTER

Each switch input has a designated 20 ms timer. The timer

starts when the specific switch input crosses the comparator

threshold (4.0 V). When the 20 ms timer expires, the contact

current is reduced from 16 to 2.0 mA for switch-to-battery

inputs and 32 to 4.0 mA for switch-to-ground inputs. The

wetting current timer may be disabled for a specific input.

When the timer is disabled, wetting current will continue to

flow through the closed switch contact. With multiple wetting

current timers disabled, power dissipation for the IC must be

considered.

The MCU may change or update the Wetting Current Timer

Register via software at any time in Normal mode. This allows

the MCU to control the amount of time wetting current is

applied to the switch contact. Programming the wetting

current timer bit to logic [0] will disable the wetting current

timer. Programming the wetting current timer bit to logic [1]

will enable the wetting current timer (refer to Table 9).

Analog Integrated Circuit Device Data

Freescale Semiconductor

33975

17

Share Link: