PHILIPS SA5778D

INTEGRATED CIRCUITS
SA5778
Serial triple gauge driver (STGD)
Product specification
Supersedes data of 1997 May 27
IC18 Data Handbook
1998 Apr 03
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
DESCRIPTION
FEATURES
The Serial Triple Gauge Driver (STGD), is a single chip air core
driver providing drive to one major gauge, and two minor gauges, for
automotive applications such as Speedometer, Fuel, Temperature,
Tachometer, Volts, and Oil pressure information display. The STGD
operates in conjunction with a microcontroller receiving serial data
inputs, and can provide status back to the microcontroller either
serially or via a status line. The protocol is compatible with the
Philips Single Gauge Driver (SGD) and Dual Gauge Driver (DGD).
The STGD also includes a protected battery supply for external
single Serial Gauge Drivers or Dual Gauge Drivers.
• Major Gauge 10-bit resolution Drive provides 0.35° resolution
PIN CONFIGURATION
• Serial Data Output
SIN+
1
28
– Sine/Cosine outputs for 360° operation
– 0.2° accuracy typical throughout entire range
• Minor gauge drivers provide 0.35° resolution
– 112° operation
– 0.5° accuracy typical throughout entire range
• Serial Data Input
– Supports interface from microcontrollers
– Compatible with Philips SGD SA5775A and DGD SA5777A
– Permits the STGD to be wired in series using a common chip
select to additional STGDs, SGDs, and DGDs
– Permits fault status information to be returned to the
microcontroller
SIN–
RUN
2
27
COS+
GOE
3
26
COS–
SwCONTROL
4
25
ST
SwBATT1
5
24
SCLK
GND
6
23
GND
GND
7
22
GND
GND
8
21
GND
GND
9
20
GND
• Over Voltage Protection, Over Temperature Protection and Low
Standby Current Operation
– Gauge drivers disabled when supply voltage exceeds specified
operating voltage, protection to 40V.
– Gauge drivers disabled when die temperature exceeds
operating range
– External switch may supply overvoltage protected battery
supply to other devices operating off battery
VBATT
10
19
CS
SwBATT2
11
18
DATAIN
DATAOUT
12
17
C1–
COM
13
16
C1+
C2–
14
15
C2+
• Thermally Enhanced SO-28 surface mount package
SR01116
Figure 1. Pin Configuration
BLOCK DIAGRAM
SCLK
MINOR GAUGE 2
DATAIN
MINOR GAUGE 1
MAJOR GAUGE
10-BIT SR
10-BIT SR
9-BIT DATA
LATCH
9-BIT DATA
LATCH
7-BIT
Tan
DAC
7-BIT
Tan
DAC
10-BIT SR
DATAOUT
CS
GOE
RUN
ST
ENABLE
7–BIT, SINE
/COSINE
DAC
SIN+
SIN–
COS+
COS–
MUX
GND
MUX
COM
C2+
C2–
SwBATT2
SwBATT1
SwControl
MUX
C1+
BIAS, TSD
SwBATT,
COMMON
REFERENCE
C1–
VBATT
4-BIT STATUS
LATCH
10-BIT DATA
LATCH
SR01117
Figure 2. STGD Internal Block Diagram
1998 Apr 03
2
853–2055 19199
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
ORDERING INFORMATION
DESCRIPTION
TEMPERATURE RANGE
ORDER CODE
DWG #
–40 to +105°C
SA5778D
SOT136-1
28-Pin Small Outline (SO) thermally enhanced Package
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PIN DESCRIPTION
Mnemonic
Pin No.
Type
GND
6,7,8,9,20,
21,22,&23
I
Circuit Ground Potential. The pins are used for heat dissipation to board. All pins should be soldered
to foil on the board per the thermal management description.
Name and Function
VBATT
10
I
Battery supply voltage
GOE
3
I
Gauge Output Enable: A high on this input enables normal operation of the gauge coil drivers.
See Table 1.
RUN
2
I
RUN (Ignition): Input to sense the state of the Ignition switch. See Table 1.
SwCONTROL
4
O
Switched Battery Control: Control output to switch on a protected VBATT supply via an external PNP
transistor. This output is controlled by the RUN input, GOE input and the on chip protection circuits.
SwBATT1
SwBATT2
5,
11
I
I
Switched Battery Supplies: Used as the reference level for the DACs, bias voltage for the second coils
of the minor gauges, and the supply for the output buffers for the major and minor gauges. One supplies
the major gauge drivers and related circuits, while the other supplies the minor gauge circuits. Both
SwBATT inputs must be connected to the control transistor as the two inputs are not connected internally.
SCLK
24
I
Serial Clock: Used to clock data into and out of the STGD. Data is shifted MSB first.
DATAIN
18
I
Data In: Data is loaded on the rising edge of SCLK and is shifted in MSB first.
DATAOUT
12
O
Data Out: Is provided to permit the STGD to pass status information back to the controlling
microcontroller, and to allow multiple devices to be connected in series.
ST
25
O
Status Output: This is an open drain output. Status outputs from several devices may be wire OR’ed
together. This output is low when the outputs are disabled due to a fault condition. The outputs may be
disabled due to shorted outputs, over temperature, power up reset, or the GOE control pin and this
condition is reflected on the ST pin. The outputs will also be disabled due to an over voltage condition,
however this is not reported on the ST pin as over voltage should be a transient condition.
CS
19
I
Chip Select: Active high chip select input. When CS is high, the part is enabled to receive data on the
DATAin pin and output data on the DATAout pin. A low to high transition of CS captures device status in
the shift register for output. A high to low transition of CS loads gauge data from the shift register into
the data latches.
SIN+
1
O
Sine Positive: Driver output to sine coil of major gauge, positive side.
SIN–
28
O
Sine Negative: Driver output to sine coil of major gauge, negative side.
COS+
27
O
Cosine Positive: Driver output to cosine coil of major gauge, positive side.
COS–
26
O
Cosine Negative: Driver output to cosine coil of major gauge, negative side.
C1+
16
O
Coil 1 Positive: Driver output to driven coil of minor gauge 1, positive side.
C1–
17
O
Coil 1 Negative: Driver output to driven coil of minor gauge 1, negative side.
C2+
15
O
Coil 2 Positive: Driver output to driven coil of minor gauge 2, positive side.
C2–
14
O
Coil 2 Negative: Driver output to driven coil of minor gauge 2, negative side.
COM
13
O
Common: Driver output for junction of bias coils for minor gauges. This output is regulated to half of
SwBATT.
ABSOLUTE MAXIMUM RATINGS
SYMBOL
VBATT
PARAMETER
RATING
UNIT
40
V
VIN1
Input voltage; Data In, CS, SCLK, GOE
–1 to +7
V
VIN2
Input voltage; SwBATT
–1 to +24
V
VIN3
Input voltage; RUN, with recommended RC Circuit
–1 to +40
V
PD
Power Dissipation (Tamb = 105°C) SO-28 Package
Battery supply voltage, with recommended 1K series resistor
1400
mw
Ambient operating temperature
–40 to +105
°C
TJ
Junction temperature1
+150/+160
°C
θJA
Thermal Impedance
See Thermal Management Section
°C/W
Tamb
NOTE:
1. 160°C junction temperature is permitted during high battery (>16V) fault operation
1998 Apr 03
3
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
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DC ELECTRICAL CHARACTERISTICS
VBATT = 8.0 to 16V; Tamb = –40 to +105°C
SYMBOL
LIMITS
PARAMETER
TEST CONDITION
Battery supply voltage
Normal operating range
8
Switched battery supply voltage
Normal operating range
7.5
16
V
Battery supply current, operating
VBATT = VBATTMAX
RL = RLMIN
0.5
ma
ISWBATT
Switched battery supply current, operating
Normal operating range
400
ma
IBATTSB
Battery supply current, standby
VBATT = 12 V
60
µA
VOH1
Output high voltage
DATAOUT, IOH = 300µA
4.0
V
VOH2
Output high voltage
SwCONTROL, IOH = 10µA
40
V
Off state output current
ST, VOH = 5 V
25
µA
Output low voltage
ST, DATAOUT, IOL = 1.5 mA
0.4
V
IOL = 50 mA @ VBATTMAX
1.5
V
IOL = 20 mA @ VBATTMIN
1.2
V
VBATT
VSWBATT
IBATT
IOH
VOL1
MIN
TYP
MAX
16
UNITS
V
SwCONTROL,
VOL2
Output low voltage
VIH
Input high voltage
CS, SCLK, DATAIN, GOE, RUN
VIL
Input low voltage
CS, SCLK, DATAIN, GOE, RUN
Battery overvoltage shutdown voltage
VBATT
IIH
Input high current
CS, SCLK, DATAIN, RUN GOE;
VIH = 3.5
IIL
Input low current
CS, SCLK, DATAIN, RUN GOE;
VIL=1.5
VOVSD
3.5
V
18
1.5
V
23
V
10
µA
10
µA
ACC1
Output function accuracy, major gauge
RL = RLMIN; major gauge, G1
–0.5
+0.5
Deg
ACC2,3
Output function accuracy, minor gauges
RL = RLMIN; minor gauges, G2 & G3
–1.0
+1.0
Deg
VDRIVE1
Coil drive voltage, major gauge
68
71
78
%
SwBATT
VDRIVE2,3
Coil drive voltage, minor gauges
70
74
80
%
SwBATT
RLMIN
Minimum coil load resistance
Tamb = 105°C
Tamb = 25°C
Tamb = –40°C
VCOM
Minor gauge bias voltage
IOB (Source or Sink)
RL = RLMIN
Ω
Ω
Ω
226
171
127
0.475 ×
SwBATT
0.525 ×
SwBATT
V
AC ELECTRICAL CHARACTERISTICS
VBATT = 7.5 to 16V; Tamb = –40 to +105°C
SYMBOL
PARAMETER
TEST CONDITION
LIMITS
MIN
TYP
MAX
625
UNITS
tCYC
Clock cycle time
FSCLK
Clock frequency
tSCLKL
SCLK LOW time
175
ns
tSCLKH
TCYC
ns
1.60
MHz
SCLK HIGH time
175
ns
tCSH
CS high to SCLK high time
75
ns
tCSL
SCLK low to CS low time
75
ns
tSU
DATAIN setup to SCLK high time
75
ns
tHD
SCLK high to DATAIN hold time
75
ns
tDR
DATAOUT rise time
0.8 to 3.6V; CL = 90pF
75
ns
tDF
DATAOUT fall time
3.6 to 0.8V; CL = 90pF
75
ns
1998 Apr 03
4
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
J1850
PROTOCOL
CONTROLLER
SA5778
4
80C51
MICRO–
CONTROLLER
SERIAL
SA5778
SERIAL
TRIPLE
GAUGE
DRIVER
AU5780
J1850 VPW
TRANSCEIVER
J1850 BUS
360° MAJOR
GAUGE
GOE
2
112° MINOR
GAUGE
2
RUN
IGNITION
ADDITIONAL GAUGE
DRIVERS; SA5775A
OR SA5777A
PROTECTED BY
SA5778
VBATT
SR01118
Figure 3. System Connections for the STGD
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.
DATAOUT
SCLK
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.
DATAIN
SCLK
PORT N
CS
DATAIN
DATAOUT
INT
5V
ST
DATAIN
SCLK
CS
ADDITIONAL
GAUGE DRIVER(S),
SA5775A,
SA5777A OR
SA5778
DATAOUT
Figure 3 shows the connection of the STGD in a typical application.
ST
SR01119
APPLICATION INFORMATION
Figure 4. Serial Communications Between STGD,
Microcontroller and Other Gauge Drivers
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 DATAIN on the rising edge of
SCLK. Several gauge drivers may be wired in series using a
common chip select and clock line, when more than three gauges
are needed. The DATAOUT pins are cascaded to the DATAIN 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.
1998 Apr 03
SA5778 SERIAL
TRIPLE
GAUGE DRIVER
MICROCONTROLLER
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.
5
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
DATAIN
SA5778
placed in a standby mode with a low on both the GOE and RUN
input pin. In this mode, battery current drain is minimized.
DATA / STATUS SHIFT REGISTERS
DATA
OUT
SCLK
STATUS
LATCH
ST
The SwBATT1 and SwBATT2 inputs are the supply for the DACs,
and the output buffers driving the coils including the COM output
which stabilizes the voltages applied to the bias coils of the minor
gauges. Both SwBATT1 and SwBATT2 should be connected to the
collector of the control transistor as these inputs are not connected
internally and supply different portions of the circuit. This switched
battery supply is protected from voltages exceeding the specified
operating range and is controlled by the SwCONTROL output. This
supply may optionally be used to supply additional circuits which
operate from unregulated battery supplies but which need protection
from over voltage transients. Typical devices which may benefit from
this protection include the Serial Gauge Driver, SA5775A and Dual
Gauge Driver, SA5777A, which are often used in conjunction with
the STGD in 4 and 5 gauge applications.
DATA
LATCHES
CS
GOE
112° MINOR GAUGES
SIN+
SIN–
COS+
COS–
GND
C1–
C1+
COM
C2–
SwBATT TRANSISTOR
C2+
SwBATT2
SwBATT1
VBATT
SwControl
DIGITAL-to-ANALOG
CONVERTERS and OUTPUT
MULTIPLEXERS
ENABLE
THERMAL
PROTECTION
SwBATT, BIAS
RUN
This switched battery supply is turned off when the STGD enters the
standby mode in response to the RUN and GOE inputs both being
low, or a VBATT supply exceeding the specified operating range. The
switched battery supply depends on the RUN signal to prevent
undesired needle movement on the minor gauges when going from
standby to active mode. This movement would otherwise occur if
the voltage to the fixed bias coils of the minor gauges was switched
on before the coil voltages provided by the DACs within the STGD
were defined. The start up jump is prevented as follows. In the sleep
mode the switched battery supply is off, and the gauge drive outputs
of the STGD are in a high impedance state. The gauges are in their
zero position from the previous power-down sequence. When the
RUN input goes high, but the GOE is kept low, the STGD enters the
start up mode in which the minor gauges are driven to zero, the
internal 5V regulator for the logic is turned on, and the switched
battery supply is turned on to supply the bias coil and STGD output
buffers. However, the output buffers for the major gauge remain in
the high impedance output state. The microcontroller may load
values into the STGD via the serial interface while GOE is low.
When the microcontroller applies a high to GOE, the major gauge
output buffers are enabled. When the RUN signal is removed the
STGD continues to operate in the normal mode, however, the
controlling microcontroller should also monitor RUN and, when it
goes low, send a series of values to the STGD to move the needles
to their zero positions before taking GOE low to put the part in the
standby mode.
360° MAJOR GAUGE
SR01120
Figure 5. Gauge Connections to the STGD
18-24V
REFERENCE
VBATT
5V
REGULATOR
+
5V
LOGIC
–
OUTPUT
BUFFER SUPPLY
1KΩ
DAC REFERENCES
GOE
SwControl
RUN
SwBATT1/2
10KΩ
RB
VBATT
BIAS COILS
EXTERNAL
GAUGE DRIVERS
SR01121
Figure 6. Gauge Enable/Standby Circuit and Over Voltage
Protection Circuit
Figure 6 shows the protection and gauge enable logic for the STGD.
The battery supply voltage VBATT is monitored, and if the supply
exceeds the specified operating range, the STGD is put in a
shutdown mode in which the output buffers are disabled. The STGD
will also enter the shutdown mode by excessive die temperature,
and will return to normal operation when the die temperature
decreases to within specified limits. Thermal shutdown may occur at
VBATT supply voltages over 16V at high ambient temperatures near
105°C. Internal logic will continue to function and status may be read
out to determine the source of the shutdown. The STGD may be
1998 Apr 03
Table 1 describes the operation and control of the SwBATT supply,
the output buffers, and the operations normally performed by the
microcontroller. Normal operation of a vehicle will follow the
sequence of the truth table from top to bottom. The RUN input is
typically connected to the switched ignition voltage, while GOE is
controlled by the microcontroller.
6
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
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Table 1. Truth Table
RUN
Input
1=High
GOE
Input
1=High
SwControl
1=ON
Swbatt1,2
Voltage
Minor Gauge Driver
Outputs
Major Gauge
Driver Outputs
0
0
0
Off
High Impedance
High
Impedance
Standby mode
1
0
1
VBATT
Enabled
(output forced to zero)
High
Impedance
Start up mode, sets minor gauge driver to
zero position, and disables major gauge
driver. Load values into STGD via the serial
port.
1
1
1
VBATT
Enabled
Enabled
Normal Operating mode. Periodically
update gauge data as required by the
application.
0
1
1
VBATT
Enabled
Enabled
Power down sequence. Load a series of
values into the STGD to return needles to
zero before power is removed.
0
0
0
Off
High Impedance
High
Impedance
Returned to standby mode (same as first
row of table)
The actual value used is dependent on the current needed to
keep the PNP in saturation.
THERMAL MANAGEMENT AND POWER
DISSIPATION
All gauges at 45° to a quadrant axis, as this is the highest
internal power dissipation position.
If only the nominal coil resistance is known at a given nominal
ambient temperature such as 25°C, the coil operating resistance at
a high temperature ambient may be calculated using the following
formula:
The power dissipated by the STGD has three components. The first
term in the equation below represents the power dissipated in the
STGD from current through the coil resistance. This component of
the power dissipation is a function of both the battery voltage and
the coil resistance. Most of the external loads such as the coils are
resistive, so the current drawn by the output buffers is proportional
to the supply voltage, resulting in power dissipation that is
proportional to the square of the supply voltage for these circuits.
RCA = RCN (1+(0.4%/°C)*((TSH+Tamb)–25°C))
Where:
The highest power dissipation for a given coil driver will occur when
the coil voltage is being driven to 50% of VBATT. Thus the power
dissipated by each coil driver is (VBATT/2)* (VBATT/2Rc) or
VBATT(VBATT/4Rc). If the coil resistance of the two minor gauge coils
and the two coils of the major gauge all have the same resistance,
then the maximum total power dissipation of the drivers becomes
4*VBATT(VBATT/4Rc) or simply VBATT(VBATT/Rc). Much of the
internal analog circuits appears to the supply pins as a current sink
and is represented by the second term. The current drawn by these
circuits is relatively constant despite changes in supply voltage,
resulting in power dissipation that is proportional to the supply
voltage. Finally some power is dissipated in driving the external PNP
transistor used to control the switched battery supply. The total
power dissipation is a combination of these components and may be
calculated from the formula:
RCA = Resistance of Coil at Ambient temperature, including self
heating
RCN = Nominal Resistance of Coil at 25°C, without self heating
Tamb = Ambient temperature, °C
TSH = Self heating of coil, °C
0.4%/°C = Resistance increase coefficient for copper
Figure 7 shows power dissipation plotted as a function of coil
resistance and voltage. Since coil resistance is a function of
temperature, the maximum power dissipation plotted will only occur
at the lowest specified operating temperature. The power dissipation
is lowest at the highest ambient temperature because of the
increase in coil resistance with temperature.
This maximum power dissipation will only occur during a fault
condition in which the system voltage rises to 18V, generally
because of a failed voltage regulator controlling the vehicles battery
voltage. Power dissipation will be lower when air core meter
movements with higher nominal coil resistance are used.
PD=VBATT(VBATT/RC)+VBATT(0.012) +
VOL2(VBATT–VOL2–VBE(PNP))/RB
Where:
PD = Power dissipation in watts
VBATT = Battery supply voltage in volts
RC = Coil resistance in ohms at ambient temperature including
any self heating effects
VOL2 = Output low voltage of the SwCONTROL pin as specified
in the DC Characteristics
VBE(PNP)= The VBE drop of the external PNP transistor
RB = Resistor is series with base of external PNP transistor.
The minimum value of RB = VBATTMAXIOL=16/0.050=320 Ω
1998 Apr 03
System Status
7
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
125
3.0
POWER
(W)
POWER DISSIPATION FOR COIL
RESISTANCE IN OHMS AND OPERATING BATTERY VOLTAGE
2.5
150
175
2.0
235
325
1.5
LOAD RESISTANCE
(Ω)
1.0
0.5
18
17.5
17
16.5
16
15.5
15
14.5
14
13.5
13
12.5
12
11.5
11
10.5
10
9.5
9
8.5
8
7.5
0.0
VSWBATT
(V)
SR01430
Figure 7. Power Dissipation of the STGD as a Function of Coil Resistance and Operating Voltage
Figure 8 shows the thermal resistance of the STGD mounted on a
PC board with heat-sinking copper on the component side only.
Figure 9 is a similar plot for a two sided PC board (same size copper
areas on each side). Both plots assume a 60 x 60 x 1.57 mm FR4
board with varying square-shaped sizes of 2 oz. copper. The two
sided board also assumes 8 thermal bias with 0.36 mm2 cross
section.
The STGD is specified to operate up to VBATTmax. The over voltage
shutdown circuit will turn off the output buffers and the switched
battery supply when the battery voltage reaches VOVSD. Over
temperature conditions will also cause the output buffers to be
disabled.
The STGD employs a thermally enhanced SO-28 package. The
center four pins on each side are fused to the die pad to create a
path for removal of heat from the package to the copper foil on the
PC board. An area of copper foil is required on the PC board for
heat dissipation at higher power dissipation levels.
It is important to note that at such a high ambient temperature (worst
case of 105°C assumed), radiation is just as significant as
convection in the dissipation of heat. Good radiation is highly
dependent on the emissivity of the heated surface, so the thermal
radiation properties of the copper foil should be considered. Bare,
clean copper is a good thermal conductor, but it has a low emissivity,
and is therefore a bad radiator. It is recommended that the copper
areas intended for heat dissipation be left covered with solder mask
or otherwise blackened to increase the emissivity, thereby improving
the heat radiating ability of the board.
In order to determine the size of the copper foil required, both
thermal testing and thermal modeling were used. The effective
ΘJA (thermal resistance, junction to ambient) was determined using
both single and double sided PCBs with heat-sinking copper foil
areas. Figures 8 and 9 show the effect of PCB copper foil area on
the effective thermal resistance of the STGD part/PCB system.
1998 Apr 03
8
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
50
ΘJA (°C/W)
45
40
1.4W LIMIT
35
30
25
0
500
1000
1500
2000
2500
3000
3500
PCB COPPER HEAT SINK AREA (SQ mm)
SR01497
Figure 8. θJA for SO28 with 8 Fused Pins
One-sided PCB (2 oz. Copper), e = 0.9, Tamb = 105°C, P = 1.4–1.8W
45
ΘJA (°C/W)
40
1.4W LIMIT
35
30
25
0
500
1000
1500
2000
2500
3000
PCB COPPER HEAT SINK AREA (SQ mm)
SR01498
Figure 9. θJA for SO28 with 8 Fused Pins
Two-sided PCB (2 oz. Copper), e = 0.9, Tamb = 105°C, P = 1.4–1.8W
1998 Apr 03
9
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
From Figure 8, the copper area required, using a single sided board,
to keep the junction temperature within limits is approximately
2200 mm2. Figure 9 shows 1200 mm2 is required on each side of a
double-sided board.
Sample Calculations for Power Dissipation and
Thermal Management
Worst Case Example
The worst case example will occur when the STGD is operating at
VBATTMAX (16V, in the highest specified ambient temperature
(105°C), and with the lowest specified coil resistance (171 ohms at
25°C). Typical coil self heating of 15°C is assumed.
The above example illustrates the worst case situation of the STGD
operating in at a maximum battery voltage, with the lowest nominal
coil resistance (171Ω at room temperature), and at the highest
ambient temperature. This will produce the highest junction
temperature. At lower ambient temperatures the power dissipation
may be higher because the coil resistance is decreased, however
the junction temperature will be lower.
Calculation of Coil resistance operating at 105°C ambient.
R
CA=
RCN (1+(0.4%W/°C)*((TSH+Tamb)–25°C))
= 171 x(1+(0.4%((15+105)–25)))
Serial Interface
= 236 Ohms at Tamb=105°C, with 15°C of self heating.
Figure 10 demonstrates the serial interface timing referenced in the
AC specifications. Figure 11 shows the order of information transfer
through the serial interface. On a low to high transition of the CS pin,
status information replaces the four most significant bits of data in
the shift register and are the first bits shifted out. Output data is
changed on the falling edge of SCLK, while input data is captured on
the rising edge of SCLK. Major gauge data is loaded first, starting
with the most significant bit, followed by minor gauge 1 data then
minor gauge 2 data.
Calculation of STGD power dissipation at 16 volt operation.
PD = VBATT (VBATT/RC) + VBATT (0.012)
+VOL2 (VBATT – VOL2 – VBE(PNP)) / RL
= 16(16/236)+16(0.012)+1.5(16–1.5–0.5)/320
= 1.085+0.192+0.066 Watts
= 1.34 Watts
Required board area and Junction Temperature calculation
The maximum junction temperature desired is 150°C. The
permissible temperature rise and required ΘJA may be calculated
as:
∆T = Tj–Tamb
ΘJA = ∆T/PD
Where; ∆T = Temperature rise in °C
PD = Power dissipation
Tj = Junction Temperature
Tamb = Ambient Temperature
∆T = TJ–Tamb = 150 – 105 = 45°C
ΘJA = ∆T/PD=55°C/1.34 watts = 33°C/W.
tCYC
tCF
tCR
tCSL
tCSH
1
SCLK
29
tSCLKL
CS
tSCLKH
30 CLOCK CYCLES
DATAIN
D29
D1
tSU
D0*
tHD
tDF
tDR
DATAOUT
30
S4
D1*
D0*
SR01499
Figure 10. Serial Interface Timing
1998 Apr 03
10
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
MINOR GAUGE 2
DATA IN
SA5778
MINOR GAUGE 1
MAJOR GAUGE/STATUS
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18 D19 D20 D21 D22 D23 D24 D25 D26 D27 D28 D29
LSB
MSB LSB
MSB LSB
DATA OUT
MSB
During Read out:
D26: RUN Input State;
1 = RUN input high
0 = RUN input low
D27: Thermal Shutdown;
1 = Shutdown
0 = Normal operation
D28: Minor Gauge Over Current;
1 = Over Current Shutdown
0 = Normal operation
D29: Major Gauge Over Current;
1 = Over Current Shutdown
0 = Normal operation
SR01123
Figure 11. Internal Shift Register
15
COS
DIFFERENTIAL OUTPUT VOLTAGE
10
SIN
5
0
0
127
255
383
511
639
767
895
1023
–5
–10
–15
INPUT CODE
SR01500
Figure 12. Major Gauge Output Voltages (VSWBATT = 14V)
1998 Apr 03
11
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
14.00
12.00
10.00
8.00
C+ – C– (VOLTS)
6.00
4.00
2.00
0.00
31
–2.00
63
95
127
159
191
223
255
287
319
INPUT CODE
–4.00
–6.00
–8.00
–10.00
–12.00
–14.00
SL00462
Figure 13. Typical Minor Gauge Output Voltage vs. Input Code (VSWBATT = 14V)
ASSUMING CODE 0 IS 0°:
0.5 x VSWBATT
CODE
–56°
+56°
0.744 x VSWBATT
–0.744 x VSWBATT
TOTAL SPAN = 112.15°
STEP SIZE = 0.35°
POSITION
0
–56.097
31
–45.194
63
–33.940
95
–22.685
127
–11.430
159
–0.176
191
11.079
223
22.333
255
33.588
287
44.843
319
56.097
IDEAL ANGLE(DEGREE)=CODE/319*2* ArcTan (0.744/0.5)–ArcTan(0.744/0.5)
SR01501
Figure 14. Minor Gauge Total Span
1998 Apr 03
12
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
120
100
ANGLE (DEGREES)
80
60
40
20
0
0
15
31
41
63
79
95
111
127
159
175
143
INPUT CODE
191
207
223
239
255
271
287
303
319
SL00464
Figure 15. Meter Position (degrees) vs. Input Code for Minor Gauges
1998 Apr 03
13
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
SO28: plastic small outline package; 28 leads; body width 7.5mm
1998 Apr 03
14
SOT136-1
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
NOTES
1998 Apr 03
15
Philips Semiconductors
Product specification
Serial triple gauge driver (STGD)
SA5778
Data sheet status
Data sheet
status
Product
status
Definition [1]
Objective
specification
Development
This data sheet contains the design target or goal specifications for product development.
Specification may change in any manner without notice.
Preliminary
specification
Qualification
This data sheet contains preliminary data, and supplementary data will be published at a later date.
Philips Semiconductors reserves the right to make chages at any time without notice in order to
improve design and supply the best possible product.
Product
specification
Production
This data sheet contains final specifications. Philips Semiconductors reserves the right to make
changes at any time without notice in order to improve design and supply the best possible product.
[1] Please consult the most recently issued datasheet before initiating or completing a design.
Definitions
Short-form specification — The data in a short-form specification is extracted from a full data sheet with the same type number and title. For
detailed information see the relevant data sheet or data handbook.
Limiting values definition — Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one
or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or
at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended
periods may affect device reliability.
Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips
Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or
modification.
Disclaimers
Life support — These products are not designed for use in life support appliances, devices or systems where malfunction of these products can
reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications
do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application.
Right to make changes — Philips Semiconductors reserves the right to make changes, without notice, in the products, including circuits, standard
cells, and/or software, described or contained herein in order to improve design and/or performance. Philips Semiconductors assumes no
responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright, or mask work right to these
products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless
otherwise specified.
 Copyright Philips Electronics North America Corporation 1998
All rights reserved. Printed in U.S.A.
Philips Semiconductors
811 East Arques Avenue
P.O. Box 3409
Sunnyvale, California 94088–3409
Telephone 800-234-7381
Date of release: 04–98
Document order number:
1998 Apr 03
16
9397 750 03715