MC33291DW Freescale Semiconductor, MC33291DW Datasheet - Page 15

• Manufacturer Part Number: MC33291DW
• Description: IC SWITCH 8X L-SIDE W/SPI 24SOIC
• Manufacturer: Freescale Semiconductor
• Type: Low Sider

Specifications of MC33291DW

• Input Type: SPI
• Number Of Outputs: 8
• On-state Resistance: 600 mOhm
• Current - Output / Channel: 500mA
• Current - Peak Output: 3A
• Voltage - Supply: 9 V ~ 26.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• For Use With: KIT33291DWEVB - KIT EVAL FOR MC33291 SMART SW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

CHIP SELECT (CS)
CS
transferred from the MCU to the 33291 by way of the SI pin
and from the 33291 to the MCU through the SO pin. Clocked-
in data from the MCU is transferred from the 33291 Shift
register and latched into the power outputs on the rising edge
of the
status information is transferred from the power outputs then
loaded into the Shift register of the device. The
controls the output driver of the serial output (SO) pin.
Whenever the
output driver is enabled allowing information to be transferred
from the 33291 to the MCU. To avoid data corruption or the
generation of spurious data, it is essential the high-to-low
transition of the
low state.
SYSTEM CLOCK (SCLK)
registers of the 33291. The serial input (SI) pin accepts data
into the Input Shift register on the falling edge of the SCLK
signal while the serial output (SO) pin shifts data information
out of the SO line driver on the rising edge of the SCLK signal.
False clocking of the Shift register must be avoided to
guarantee validity of data. It is essential the SCLK pin be in a
logic low state whenever the chip select bar (
any transition. For this reason, it is recommended, though not
absolutely necessary, the SCLK pin be kept in a low logic
state as long as the device is not accessed (
state). When
and SI pins are ignored and SO is tri-stated (high
impedance). See the Data Transfer Timing diagram in
Figure
SERIAL INSTRUCTION (SI)
read on the falling edge of SCLK. A logic high state present
on this pin when the SCLK signal rises will program a specific
output OFF. In turn,
the rising edge of the
present on the SI pin will program the output ON, In turn, the
pin turns ON the specific output on the rising edge of the
signal.
8-bit serial stream of data is required to be synchronously
entered into the SI pin starting with Output 7, followed by
Output 6, Output 5, and so on, to Output 0. Referring to
Figure
corresponding to Output 7. For each rise of the SCLK signal,
with
OFF) is synchronously loaded into the Shift register per the
Analog Integrated Circuit Device Data
Freescale Semiconductor
The 33291 receives its MCU communication through the
The system clock (SCLK) pin clocks the internal shift
This pin is for the input of serial instruction (SI) data. SI is
To program the eight outputs of the 33291 ON or OFF, an
pin. Whenever this pin is in a logic low state, data can be
CS
CS
18, page 17.
18, the DO bit is the most significant bit (MSB)
held in a logic low state, a data-bit instruction (ON or
signal. On the falling edge of the
CS
CS
CS
is in a logic high state, signals at the SCLK
pin goes to a logic low state, the SO pin
signal occur only when SCLK is in a logic
CS
CS
pin turns OFF the specific output on
signal. Conversely, a logic low state
CS
FUNCTIONAL PIN DESCRIPTION
CS
CS
signal, drain
CS
in logic high
) pin makes
pin also
CS
data-bit SI state. The Shift register is full after eight bits of
information have been entered. To preserve data integrity,
care should be taken to not transition SI as SCLK transitions
from a low-to-high logic state.
SERIAL OUTPUT (SO)
the Shift register. The SO pin remains in a high impedance
state until the
reports the drain status, either high or low relative to the
previous command word. The SO pin changes state on the
rising edge of SCLK and reads out on the falling edge of
SCLK. When an output is OFF and not faulted, the
corresponding SO data-bit is a high state. When an output is
ON, and there is no fault, the corresponding data-bit on the
SO pin will be a low logic state. The SI/SO shifting of data
follows a first-in-first-out (FIFO) protocol with both input and
output words transferring the MSB first. Referring to
Figure
relative to the previous command word. The SO pin is not
affected by the status of the
RESET (RST)
the SPI Shift register. In doing so, all output switches are set
at OFF. With the device in a system with an MCU, upon initial
system power-up, the MCU holds the
in a logic low state, ensuring all outputs to be OFF until both
the V
operation. After the 33291 is reset, the MCU is ready to
assert system control with all output switches initially OFF.
following normal operation, the MCU should pull the
low to shut down the outputs and clear the input data register.
The
incorporated to ensure operational predictability should the
external pull-down of the MCU open circuit. The internal pull-
down is only 25 A, affording safe and easy interfacing to the
MCU. The
low state for a duration of at least 250 ns to ensure reliable a
reset.
programmed through the use of an RC network comprised of
a shunt capacitor from the
to V
ensuring proper discharge of the capacitor. Careful attention
eliminates adverse delay of the
if it pulls the Reset line low, thereby accomplishing
initialization for turn ON delay. It may be easier to incorporate
delay into the software program and use a parallel port pin of
the MCU to control the 33291
The serial output (SO) pin is the tri-stateable output from
The 33291 Reset (
If the V
A simple power ON reset delay of the system can be
DD
RST
DD
, illustrated in
18, the DO bit is the MSB corresponding to Output 7
and V
pin is active low and has an internal pull-down
PWR
RST
CS
PWR
pin of the 33291 experiences a low voltage,
pin of the 33291 should be pulled to a logic
pin goes to a logic low state. The SO data
pin voltages are adequate for predictable
Figure
RST
) pin is active low. It is used to clear
RST
17. Care should be exercised
RST
FUNCTIONAL PIN DESCRIPTION
RST
RST
pin to Ground and a resistor
FUNCTIONAL DESCRIPTION
pin.
pin.
and damage of the MCU
RST
pin of the device
RST
33291
pin
15