33879 Datasheet, PDF (15/24 Pages) Freescale Semiconductor, Inc – Configurable Octal Serial Switch with Open Load Detect Current Disable

FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
CS PIN
The system MCU selects the 33879 with which to
communicate through the use of the chip select CS pin. Logic
low on CS enables the data output (DO) driver and allows
data to be transferred from the MCU to the 33879 and vice
versa. Data clocked into the 33879 is acted upon on the rising
edge of CS.
To avoid any spurious data, it is essential the high-to-low
transition of the CS signal occur only when SPI clock (SCLK)
is in a logic low state.
SCLK PIN
The SCLK pin clocks the internal shift registers of the
33879. The serial data input (DI) pin is latched into the input
shift register on the falling edge of the SCLK. The serial data
output (DO) pin shifts data out of the shift register on the
rising edge of the SCLK signal. False clocking of the shift
register must be avoided to ensure validity of data. It is
essential that the SCLK pin be in a logic low state when the
CS pin makes any transition. For this reason, it is
recommended the SCLK pin is commanded to a logic low
state when the device is not accessed (CS in logic high state).
With CS in a logic high state, signals present on SCLK and DI
are ignored and the DO output is tri-state.
DI PIN
The DI pin is used for serial instruction data input. DI
information is latched into the input register on the falling
edge of SCLK. A logic high state present on DI will program
a specific output on. The specific output will turn on with the
rising edge of the CS signal. Conversely, a logic low state
present on the DI pin will program the output off. The specific
output will turn off with the rising edge of the CS signal. To
program the eight outputs and Open Load Detection Current
on or off, send the DI data beginning with the Open Load
Detection Current bits, followed by output eight, output
seven, and so on to output one. For each falling edge of the
SCLK while CS is logic low, a data bit instruction (on or off) is
loaded into the shift register per the data bit DI state. Sixteen
bits of entered information is required to fill the input shift
register.
DO PIN
The DO pin is the output from the shift register. The DO pin
remains tri-state until the CS pin is in a logic low state. All
faults on the 33879 device are reported as logic [1] through
the DO data pin. Regardless of the configuration of the driver,
open loads and shorted loads are reported as logic [1].
Conversely, normal operating outputs with non-faulted loads
are reported as logic [0]. Outputs programmed with Open
Load Detection Current disabled will report logic [0] in the off
state. The first eight positive transitions of SCLK will report
logic [0] followed by the status of the eight output drivers. The
DI / DO shifting of data follows a first-in, first-out protocol with
both input and output words transferring the most significant
bit (MSB) first.
EN PIN
The EN pin on the 33879 enables the device. With the EN
pin high, output drivers may be activated and open / short fault
detection performed and reported. With the EN pin low, all
outputs become inactive, Open Load Detection Current is
disabled, and the device enters Sleep mode. The 33879 will
perform Power-ON Reset on rising edge of the enable signal.
IN5 AND IN6 PINS
The IN5 and IN6 command inputs allow outputs five and
six to be used in PWM applications. The IN5 and IN6 pins are
OR-ed with the Serial Peripheral Interface (SPI) command
input bits. For SPI control of outputs five and six, the IN5 and
IN6 pins should be grounded or held low by the
microprocessor. When using IN5 or IN6 to PWM the output,
the control SPI bit must be logic [0]. Maximum PWM
frequency for each output is 2.0 kHz.
V_DD PIN
The V_DD input pin is used to determine logic levels on the
microprocessor interface (SPI) pins. Current from V_DD is
used to drive DO output and the pullup current for CS. V_DD
must be applied for normal mode operation. The 33879
device will perform Power-ON Reset with the application of
V_DD.
V_PWR PIN
The V_PWR pin is battery input and Power-ON Reset to the
33879 IC. The V_PWR pin has internal reverse battery
protection. All internal logic current is provided from the V_PWR
pin. The 33879 will perform Power-ON Reset with the
application of V_PWR.
D1– D8 PINS
The D1 to D8 pins are the open-drain outputs of the 33879.
For high-side drive configurations, the drain pins are
connected to battery supply. In low-side drive configurations,
the drain pins are connected to the low side of the load. All
outputs may be configured individually as desired. When
configured as low-side drive, the 33879 limits the positive
inductive transient to 45 V.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33879
15