33880 Datasheet, PDF (13/25 Pages) Freescale Semiconductor, Inc – Configurable Octal Serial Switch with Serial Peripheral Interface I/O

FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 33880 is an eight-output hardware configurable power
switch with 8-bit serial control. The 33880 incorporates
SMARTMOS™ 5 technology with CMOS logic, bipolar/MOS
analog circuitry, and independent double diffused DMOS
power output transistors. Many benefits are realized as a
direct result of using this mixed technology. A simplified
internal block diagram of the 33880 is shown in Figure 2,
page 2.
The 33880 device uses high-efficiency updrain power
DMOS output transistors exhibiting low drain-to-source ON
resistance values (R_DS(ON) ≤ 0.55 Ω at 25°C) and dense
CMOS control logic. All outputs have independent voltage
clamps to provide fast inductive turn-off and transient
protection. Operational bias currents of less than 4.0 mA on
V_DD and 12 mA on V_PWR with any combination of outputs ON
are a direct result of using SMARTMOS™ 5 technology.
FUNCTIONAL PIN DESCRIPTION
CHIP SELECT (CS)
The system MCU selects the 33880 to communicate
through the use of the CS pin. Whenever the pin is in a logic
low state, data can be transferred from the MCU to the 33880
device and vice versa. Clocked-in data from the MCU is
transferred from the 33880 shift register and latched into the
power outputs on the rising edge of the CS signal. On the
falling edge of the CS signal, output status information is
transferred from the power outputs status register into the
device's shift register. The falling edge of CS enables the DO
output driver. Whenever the CS pin goes to a logic low state,
the DO pin output is enabled, thereby allowing information to
be transferred from the 33880 to the MCU. To avoid any
spurious data, it is essential the high-to-low transition of the
CS signal occurs only when SCLK is in a logic low state.
SYSTEM CLOCK (SCLK)
The system clock pin (SCLK) clocks the internal shift
registers of the 33880. The serial data input (DI) is latched
into the input shift register on the falling edge of the SCLK.
The serial data output pin (DO) 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 guarantee validity of
data. It is essential the SCLK pin be in a logic low state
whenever chip select pin (CS) 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). When the CS is in a logic high state, any signal at
the SCLK and DI pin is ignored and the DO is tri-stated (high
impedance).
DATA INPUT (DI)
This 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 of the 33880 device on or off, enter
Analog Integrated Circuit Device Data
Freescale Semiconductor
the DI pin beginning with Output 8, followed by Output 7,
Output 6, and so on to Output 1. 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. Eight
bits of entered information fills the shift register. To preserve
data integrity, do not transition DI as SCLK transitions from a
high to low logic state.
DATA OUTPUT (DO)
The serial data output (DO) pin is the output from the shift
register. The DO pin remains tri-state until the CS pin goes to
a logic low state. All faults on the 33880 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]. The first
positive transition of SCLK will make output eight status
available on DO pin. Each successive positive clock will
make the next output status available. 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.
ENABLE (EN)
The EN pin on the 33880 device either enables or disables
the internal charge pump. The EN pin must be high for this
device to enhance the gates of the output drivers, perform
fault detection, and reporting. Active outputs during a low
transition of the EN pin will become active again when the EN
transitions high. If this feature is not required, it is
recommended the EN pin be connected to V_DD.
COMMAND INPUT (IN5 AND IN6)
The IN5 and IN6 pins command inputs allowing outputs
five and six to be used in PWM applications. IN5 and IN6 pins
are ORed with the SPI communication input. For SPI control
of outputs five and six, the IN5 and IN6 pins should be
grounded or held low by the microprocessor. In the same
manner, when using the PWM feature the SPI port must
command the outputs off. Maximum PWM frequency for each
output is 2.0 kHz.
33880
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