SA5778 Datasheet, PDF (5/16 Pages) NXP Semiconductors – Serial triple gauge driver STGD

Philips Semiconductors
Serial triple gauge driver (STGD)
Product specification
SA5778
J1850
PROTOCOL
CONTROLLER
AU5780
J1850 VPW
TRANSCEIVER
J1850 BUS
80C51
MICRO–
CONTROLLER
GOE
SERIAL
SA5778
SERIAL
TRIPLE
GAUGE
DRIVER
ADDITIONAL GAUGE
DRIVERS; SA5775A
OR SA5777A
PROTECTED BY
SA5778
Figure 3. System Connections for the STGD
4
360° MAJOR
GAUGE
2
112° MINOR
GAUGE
2
RUN
IGNITION
V_BATT
SR01118
FUNCTIONAL DESCRIPTION
Figure 1 shows the pin-out of the STGD, which is packaged in an
SO-28 pin package, enhanced for improved thermal management.
Four pins on each side of the package serve as a heat spreader to
remove heat from the die, and also function as the ground
connection. The recommended mounting includes an area of copper
on the PC board to aid in thermal management.
Figure 2 is a block diagram of the STGD. A serial interface connects
the STGD to the microcontroller. A data output pin is provided to
permit the STGD to be wired in series with other Philips air core
gauge drivers such as the Serial Gauge Driver, SA5775, and the
Dual Gauge Driver, SA5777 or additional STGDs. Status information
may be passed back to the microcontroller via a status output, or via
the serial interface.
Figure 3 shows the connection of the STGD in a typical application.
APPLICATION INFORMATION
Figure 4 demonstrates the connections between the STGD, the
microcontroller, and optionally additional gauge drivers such as the
SGD and DGD. With an active high on the chip select input (CS),
data is shifted into the STGD through DATA_IN on the rising edge of
S_CLK. Several gauge drivers may be wired in series using a
common chip select and clock line, when more than three gauges
are needed. The DATA_OUT pins are cascaded to the DATA_IN pins of
the following gauge drivers. Status information can be returned to
the microcontroller via the ST pins of each gauge driver. These are
open-drain, active low outputs, which may be wire OR’ed together to
signal that a fault, such as a thermal shut down, has occurred within
one of the gauge drivers. This pin may be connected to a
microcontroller port pin for polling in software, or may be connected
to an external interrupt input to cause entry into an interrupt service
routine. The STGD, may also pass status information back to the
microcontroller serially. The rising edge of chip select loads status
information into the shift register for the first four bits that will be
shifted out of the STGD by the shift clock. Figure 11 shows the data
bits within the shift register. A low on the ST pin signals that one or
more status bits have been set in the status register. A high
indicates all status bits are reset. The status output bits include
minor gauge over current, major gauge over current, thermal
shutdown and RUN. Gauge data is captured in latches by the falling
edge of the chip select.
MICRO-
CONTROLLER
DATA_OUT
S_CLK
PORT N
DATA_IN
INT
DATA_IN
S_CLK
CS
DATA_OUT
ST
SA5778 SERIAL
TRIPLE
GAUGE DRIVER
ADDITIONAL
5V
DATA_IN
GAUGE DRIVER(S),
SA5775A,
S_CLK
CS
SA5777A OR
SA5778
DATA_OUT
ST
SR01119
Figure 4. Serial Communications Between STGD,
Microcontroller and Other Gauge Drivers
Figure 5 shows the gauge connections to the STGD. The major
gauge, G1, supports full 360° operation with two coils driven. The
seven least significant bits of the gauge information are converted to
an analog level by digital-to-analog converter. The display range is
divided into eight sections, two sections per quadrant. The coils are
driven with a Sine/Cosine approximation. The three most significant
bits of gauge display information control the multiplexer to select
which coil is fed by the DAC and which coil receives a fixed bias.
The multiplexer also determines the polarity of the voltages supplied
to the coils.
The minor gauges, G2 and G3, each have one coil driven by a DAC.
The other coils of each gauge are wired in series with the switched
battery supply to supply the bias. The switched battery supply is
turned off during over voltage conditions. Only 9-bits of information
are required for the minor gauges, however, 10-bits are shifted
through the part to maintain compatibility with the SGD and DGD.
Hence, all gauges, both major and minor, are supplied with 10-bit
data for consistency.
1998 Apr 03
5