33972 datasheet(13/28 Pages) FREESCALE

13 / 28 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33972

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

POWER SUPPLY

The 33972 is designed to operate from 5.5 V to 40 V on

the VPWR pin. Characteristics are provided from 8.0 V to

16 V for the device. Switch contact currents and the internal

logic supply are generated from the VPWR pin. The VDD

supply pin is used to set the SPI communication voltage

levels, current source for the SO driver, and pullup current on

INT

and CS.

VDD supply may be removed from the device to reduce

quiescent current. If VDD is removed while the device is in

Normal mode, the device will remain in Normal mode. If VDD

is removed in Sleep mode, the device will remain in Sleep

mode until wake-up input is received (WAKE HIGH to LOW,

switch input or interrupt timer expires).

Removing VDD from the device disables SPI

communication and will not allow the device to wake up from

INT

and CS pins.

POWER-ON RESET (POR)

Applying VPWR to the device will cause a Power-ON Reset

and place the device in Normal mode.

Default settings from Power-ON Reset via VPWR or Reset

Command are as follows:

• Programmable Switch – Set to Switch to Battery

• All Inputs Set as Wake-Up

• Wetting Current On (16 mA)

• Wetting Current Timer On (20 ms)

• All Inputs Tri-State

• Analog Select 00000 (No Input Channel Selected)

NORMAL AND SLEEP MODES

The 33972 has two operating modes, Normal mode and

Sleep mode. A discussion on Normal mode begins below.

A discussion on Sleep mode begins on page 18.

Normal Mode

Normal mode may be entered by the following events:

• Application of VPWR to the IC

• Change-of-Switch State (when enabled)

• Falling Edge of WAKE

• Falling Edge of INT (with VDD = 5.0 V and WAKE at

Logic [1])

• Falling Edge of CS (with VDD = 5.0 V)

• Interrupt Timer Expires

Only in Normal mode with VDD applied can the registers of

the 33972 be programmed through the SPI.

The registers that may be programmed in Normal mode

are listed below. Further explanation of each register is

provided in subsequent paragraphs.

•Programmable Switch Register (Settings Command)

•Wake-Up/Interrupt Register (Wake-Up/Interrupt

Command)

•Wetting Current Register (Metallic Command)

•Wetting Current Timer Register (Wetting Current Timer

Enable Command)

•Tri-State Register (Tri-State Command)

•Analog Select Register (Analog Command)

•Calibration of Timers (Calibration Command)

•Reset (Reset Command)

Figure 6, page 9, is a graphical description of the device

operation in Normal mode. Switch states are latched into the

input register on the falling edge of CS. The INT to the MCU

is cleared on the rising edge of CS. However, INT will not

clear on rising edge of CS if a switch has closed during SPI

communication (CS LOW). This prevents switch states from

being missed by the MCU.

PROGRAMMABLE SWITCH REGISTER

Inputs SP0 to SP7 may be programmable for switch-to-

battery or switch-to-ground. These inputs types are defined

using the settings command (Table 6). To set an SPn input

for switch-to-battery, a logic [1] for the appropriate bit must be

set. To set an SPn input for switch-to-ground, a logic [0] for

the appropriate bit must be set. The MCU may change or

update the Programmable Switch Register via software at

any time in Normal mode. Regardless of the setting, when the

SPn input switch is closed a logic [1] will be placed in the

Serial Output Response Register (Table 17, page 18).

WAKE-UP/INTERRUPT REGISTER

The Wake-Up/Interrupt Register defines the inputs that

are allowed to wake the 33972 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 (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 6. Settings Command

Settings Command

Not used

Battery/Ground Select

sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0

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