33884 Datasheet, PDF (11/21 Pages) Freescale Semiconductor, Inc – Switch Monitor Interface

FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
SYNCHRONIZATION (SYNC)
The Synchronization (SYNC) input is used by the slave IC
during the Polling mode. The SYNC allows multiple 33884
ICs to poll the multiple inputs concurrently. The master
controls the polling period. The slave is allowed to shut down
it’s oscillator, thereby conserving current. When the slave
receives the SYNC signal from the master, the slave starts
the internal oscillator and reads the switch inputs.
INTERRUPT (INT)
The Interrupt (INT) pin is an interrupt output from the
33884. The INT pin is an open drain output with an internal
pull-up. In the Normal mode, a switch state change triggers
the INT pin. The INT pin and INT bit (flag) are latched on the
falling edge of CS. This procedure determines the interrupt
origin. The flag INT bit in the SPI word is the inverse of the
INT pin. The INT pin is cleared on the rising edge of CS. The
INT pin is active only during the ON time (when sink and
source currents are active) in the Polling mode.
RESET (RST)
The Reset (RST) pin is active low reset input to the 33884.
When asserted, the 33884 will reset all internal registers,
timers, and enters a Sleep mode (with all switch inputs in a
Tri-State condition). Only an MCU SPI command word will
wake the 33884 from a Sleep state. The RST pin may be
controlled directly from a general purpose input/output
(GPIO) pin or from a system/MCU reset.
BANDGAP VOLTAGE (VBG)
The Bandgap Voltage (VBG) pin requires a 130 kΩ to
ground for standard wetting and sustain currents. The device
is tested with a 0.1 percent value, but a standard 1.0 percent
could be used to function properly.
VOLTAGE POWER (VPWR)
The Voltage Power (VPWR) pin is battery/supply source
pin for the 33884. The VPWR pin requires external reverse
battery/supply and transient protection. Maximum input
voltage on VPWR is 40 V. All wetting currents and sustain
currents are derived from VPWR.
SWITCH PINS (SP1 : SP4)
The 33884 has four programmable switch sense inputs
(SP1- P4) to read switch-to-ground or switch-to-battery/
supply contacts. Transient battery/supply voltages greater
than 40 V must be clamped by an external device. Surface
mount 0805 MOVs and transient voltage suppressors (TVS)
are available in SOT-23 packages. The sensed input is
compared with an internal 4.0 V reference. When
programmed to sense switch-to-battery, sensed voltages
greater than 4.0 V are interpreted as a CLOSED switch, while
sensed voltages less than 4.0 V are interpreted as an OPEN
switch. The opposite holds true when inputs are programmed
to sense switch-to-ground. Further programming can set the
wetting currents or make the inputs Tri-State. Programming
methods are provided in the following section.
SWITCH-TO-BATTERY (SB1 AND SB2)
The two Switch-to-Battery (SB) pins sense inputs only.
Transient battery/supply voltages greater than 40 V must be
clamped by an external device. Surface mount 0805 MOVs
and transient voltage suppressors (TVS) are available in
SOT-23 packages.
The sensed input is compared with an internal 4.0 V
reference. Voltages greater than 4.0 V are interpreted as a
CLOSED switch, while sensed voltages less than 4.0 V are
interpreted as an OPEN switch. Programming can set wetting
currents or Tri-State the input. Programming methods are
provided in the following section.
SWITCH-TO-GROUND (SG1 : SG6)
The six Switch-to-Ground (SG) pins are inputs only. The
input is compared with the internal 4.0 V reference. Voltages
greater than 4.0 volts are interpreted as an OPEN switch.
Voltages less than 4.0 V are interpreted as a CLOSED
switch. Programming can set the wetting currents or Tri-State
the input. Programming methods are provided in the
following section.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33884
11