Datasheet SA5778 Datasheet (Philips)

INTEGRATED CIRCUITS

SA5778

Serial triple gauge driver (STGD)

Product specification
Supersedes data of 1997 May 27
IC18 Data Handbook

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

1998 Apr 03

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

DESCRIPTION

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.

PIN CONFIGURATION

SIN+

1

RUN

2

GOE

3

SwCONTROL

SwBATT1

SwBATT2

DATA

4
5

GND GND

6

GND

7

GND GND

821

GND GND

9

V

10

BATT

11
12

OUT

COM

13

C2–

14

SIN–

28

COS+

27
26

COS–
ST

25
24

S

CLK

23

GND

22

20

CS

19

DATA

18

IN

C1–

17

C1+

16

C2+

15

FEATURES

•Major Gauge 10-bit resolution Drive provides 0.35° resolution

– 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

•Serial Data Output

– 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

•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

•Thermally Enhanced SO-28 surface mount package

Figure 1. Pin Configuration

BLOCK DIAGRAM

S

CLK

DATA

IN

CS

GOE

RUN

V

BATT

BIAS, TSD

SwBATT,

COMMON

REFERENCE

SwBATT1

SwControl

SR01116

MINOR GAUGE 2

10-BIT SR 10-BIT SR 10-BIT SR

9-BIT DATA

ENABLE

SwBATT2

MINOR GAUGE 1 MAJOR GAUGE

LATCH

7-BIT

MUX

C2–

Tan

DAC

C2+

9-BIT DATA

LATCH

7-BIT

Tan

DAC

MUX MUX

C1–

COM

C1+

GND

10-BIT DATA

LATCH

COS–

Figure 2. STGD Internal Block Diagram

7–BIT, SINE

/COSINE

DAC

SIN–

COS+

4-BIT STATUS

LATCH

SIN+

DATA

ST

OUT

SR01117

1998 Apr 03 853–2055 19199

2

Philips Semiconductors Product specification

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SA5778Serial triple gauge driver (STGD)

ORDERING INFORMATION

DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG #

28-Pin Small Outline (SO) thermally enhanced Package –40 to +105°C SA5778D SOT136-1

PIN DESCRIPTION

Mnemonic

GND

V

BATT

GOE

ÁÁÁ

RUN

SwCONTROL

ÁÁÁ

SwBATT1
SwBATT2

ÁÁÁ

ÁÁÁ

S

CLK

DATA

IN

DATA

OUT

ÁÁÁ

ST

ÁÁÁ

ÁÁÁ

CS

ÁÁÁ

ÁÁÁ

SIN+

SIN–
COS+
COS–

C1+
C1–
C2+
C2–

COM

ÁÁÁ

Pin No.

6,7,8,9,20,

21,22,&23

10

3

ÁÁ

2
4

ÁÁ

5,

11

ÁÁ

ÁÁ

24
18
12

ÁÁ

25

ÁÁ

ÁÁ

19

ÁÁ

ÁÁ

1
28
27
26
16
17
15
14
13

ÁÁ

Type

I

Circuit Ground Potential. The pins are used for heat dissipation to board. All pins should be soldered

Name and Function

to foil on the board per the thermal management description.

I

Battery supply voltage

I

Gauge Output Enable: A high on this input enables normal operation of the gauge coil drivers.
See Table 1.

ББББББББББББББББББББББББ

I

RUN (Ignition): Input to sense the state of the Ignition switch. See Table 1.

O

Switched Battery Control: Control output to switch on a protected V

ББББББББББББББББББББББББ

transistor. This output is controlled by the RUN input, GOE input and the on chip protection circuits.

I

Switched Battery Supplies: Used as the reference level for the DACs, bias voltage for the second coils

I

of the minor gauges, and the supply for the output buffers for the major and minor gauges. One supplies

ББББББББББББББББББББББББ

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.

ББББББББББББББББББББББББ

I

Serial Clock: Used to clock data into and out of the STGD. Data is shifted MSB first.

I

Data In: Data is loaded on the rising edge of S

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.

ББББББББББББББББББББББББ

O

Status Output: This is an open drain output. Status outputs from several devices may be wire OR’ed

and is shifted in MSB first.

CLK

supply via an external PNP

BATT

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

ББББББББББББББББББББББББ

condition is reflected on the ST pin. The outputs will also be disabled due to an over voltage condition,

ББББББББББББББББББББББББ

however this is not reported on the ST pin as over voltage should be a transient condition.

I

Chip Select: Active high chip select input. When CS is high, the part is enabled to receive data on the

pin and output data on the DATA

DATA

in

ББББББББББББББББББББББББ

the shift register for output. A high to low transition of CS loads gauge data from the shift register into
the data latches.

ББББББББББББББББББББББББ

O

Sine Positive: Driver output to sine coil of major gauge, positive side.

O

Sine Negative: Driver output to sine coil of major gauge, negative side.

O

Cosine Positive: Driver output to cosine coil of major gauge, positive side.

O

Cosine Negative: Driver output to cosine coil of major gauge, negative side.

O

Coil 1 Positive: Driver output to driven coil of minor gauge 1, positive side.

O

Coil 1 Negative: Driver output to driven coil of minor gauge 1, negative side.

O

Coil 2 Positive: Driver output to driven coil of minor gauge 2, positive side.

O

Coil 2 Negative: Driver output to driven coil of minor gauge 2, negative side.

O

Common: Driver output for junction of bias coils for minor gauges. This output is regulated to half of

ББББББББББББББББББББББББ

SwBATT.

pin. A low to high transition of CS captures device status in

out

ABSOLUTE MAXIMUM RATINGS

SYMBOL

V

VIN1
VIN2
VIN3

T

BATT

P

amb

T

θ

Battery supply voltage, with recommended 1K series resistor
Input voltage; Data In, CS, SCLK, GOE
Input voltage; Sw

BATT

Input voltage; RUN, with recommended RC Circuit
Power Dissipation (T

D

Ambient operating temperature
Junction temperature

J

Thermal Impedance

JA

NOTE:

1. 160°C junction temperature is permitted during high battery (>16V) fault operation

1998 Apr 03

PARAMETER

= 105°C) SO-28 Package

amb

1

3

RATING

40

–1 to +7
–1 to +24
–1 to +40

1400

–40 to +105

+150/+160

See Thermal Management Section

UNIT

V
V
V
V

mw

°C
°C

°C/W

Philips Semiconductors Product specification

SYMBOL

PARAMETER

TEST CONDITION

UNITS

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SYMBOL

PARAMETER

TEST CONDITION

UNITS

SA5778Serial triple gauge driver (STGD)

DC ELECTRICAL CHARACTERISTICS

V

= 8.0 to 16V; T

BATT

V

BATT

V

SWBATT

I

BATT

I

SWBATT

I

BATTSB

V

OH1

V

OH2

I

OH

V

OL1

V

OL2

V

IH

V

IL

V

OVSD

I

ÁÁ

IH

I

IL

ÁÁ

ACC1

ACC2,3
V

DRIVE1

ÁÁ

V

DRIVE2,3

R

LMIN

V

COM

Battery supply voltage
Switched battery supply voltage

Battery supply current, operating
Switched battery supply current, operating

Battery supply current, standby
Output high voltage
Output high voltage
Off state output current
Output low voltage

Output low voltage

Input high voltage
Input low voltage
Battery overvoltage shutdown voltage

Input high current

БББББББББ

Input low current

БББББББББ

Output function accuracy, major gauge
Output function accuracy, minor gauges

Coil drive voltage, major gauge

БББББББББ

Coil drive voltage, minor gauges

Minimum coil load resistance

Minor gauge bias voltage

= –40 to +105°C

amb

MIN

Normal operating range
Normal operating range
V

= V

BATT

RL = R

BATTMAX

LMIN

8

7.5

Normal operating range
V

= 12 V

BATT

DATA
SwCONTROL, IOH = 10µA

, IOH = 300µA

OUT

4.0
40

ST, VOH = 5 V
ST, DATA

, IOL = 1.5 mA

OUT

SwCONTROL,

IOL = 50 mA @ V
IOL = 20 mA @ V

CS, SCLK, DATAIN, GOE, RUN

BATTMAX
BATTMIN

3.5

CS, SCLK, DATAIN, GOE, RUN
V

BATT

CS, SCLK, DATAIN, RUN GOE;

ББББББББ

V

= 3.5

IH

18

ÁÁÁÁÁÁÁ

CS, SCLK, DATAIN, RUN GOE;

=1.5

V

IL

ББББББББ

RL = R
RL = R

ББББББББÁÁÁ

; major gauge, G1

LMIN

; minor gauges, G2 & G3

LMIN

ÁÁÁÁÁÁÁ

–0.5
–1.0

68

70

T

= 105°C

amb

T

= 25°C

amb

T

= –40°C

amb

IOB (Source or Sink)
R

= R

L

LMIN

226
171
127

0.475 ×
Sw

BATT

LIMITS

TYP

71

ÁÁ

74

MAX

16
16

0.5

400

60

25

0.4

1.5

1.2

1.5
23

10

10

+0.5
+1.0

78

Á

80

0.525 ×
Sw

BATT

V
V

ma

ma
µA

V
V

µA

V

V
V

V
V
V

µA

ÁÁ

µA

ÁÁ

Deg
Deg

%

ÁÁ

Sw

BATT

%

Sw

BATT

Ω
Ω
Ω

V

AC ELECTRICAL CHARACTERISTICS

V

BATT

F
t

SCLKL

t

SCLKH

1998 Apr 03

= 7.5 to 16V; T

t

CYC
SCLK

Clock cycle time
Clock frequency
SCLK LOW time
SCLK HIGH time

t

CSH

t

CSL

t
t
t
t

CS high to SCLK high time
SCLK low to CS low time
DATAIN setup to SCLK high time

SU

SCLK high to DATAIN hold time

HD

DATAOUT rise time

DR

DATAOUT fall time

DF

= –40 to +105°C

amb

T

CYC

0.8 to 3.6V; CL = 90pF

3.6 to 0.8V; CL = 90pF

4

MIN

625

175
175

75
75
75
75

LIMITS

TYP

MAX

1.60

75
75

ns

MHz

ns
ns
ns
ns
ns
ns
ns
ns

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

J1850

PROTOCOL

CONTROLLER

AU5780

J1850 VPW

TRANSCEIVER

J1850 BUS

80C51

MICRO–

CONTROLLER

ADDITIONAL GAUGE

DRIVERS; SA5775A

OR SA5777A

PROTECTED BY

SA5778

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.

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.

GOE

SERIAL

SA5778
SERIAL
TRIPLE
GAUGE

DRIVER

MICRO­CONTROLLER

DATA

PORT N

DATA

5V

S

OUT

CLK

INT

4

2

2

V

IN

RUN

IGNITION

BATT

360° MAJOR

GAUGE

112° MINOR

GAUGE

SR01118

DATA

IN

S

CLK

CS
DATA

OUT

ST

DATA

IN

S

CLK

CS
DATA

OUT

ST

SA5778 SERIAL

TRIPLE

GAUGE DRIVER

ADDITIONAL

GAUGE DRIVER(S),

SA5775A,

SA5777A OR

SA5778

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

. Several gauge drivers may be wired in series using a

S

CLK

common chip select and clock line, when more than three gauges
are needed. The DATA

pins are cascaded to the DATAIN pins of

OUT

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.

on the rising edge of

IN

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

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

placed in a standby mode with a low on both the GOE and RUN

DATA

IN

S

CLK

ST

CS

GOE

PROTECTION
SwBATT, BIAS

SwControl

SwBATT TRANSISTOR

V

BATT

RUN

THERMAL

DATA / STATUS SHIFT REGISTERS

STATUS

LATCH

DIGITAL-to-ANALOG

CONVERTERS and OUTPUT

MULTIPLEXERS

ENABLE

C2–

C2+

COM

SwBATT2

SwBATT1

C1–

LATCHES

C1+

DATA

GND

COS–

360° MAJOR GAUGE112° MINOR GAUGES

COS+

SIN–

DATA

OUT

SIN+

SR01120

Figure 5. Gauge Connections to the STGD

18-24V

REFERENCE

V

BATT

1KΩ

GOE

RUN

10KΩ

+
–

R

B

V

BATT

5V

REGULATOR

OUTPUT
BUFFER SUPPLY

DAC REFERENCES

SwBATT1/2SwControl

BIAS COILS

EXTERNAL
GAUGE DRIVERS

5V

LOGIC

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 V

is monitored, and if the supply

BATT

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
V

supply voltages over 16V at high ambient temperatures near

BATT

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

input pin. In this mode, battery current drain is minimized.
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.

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 V

supply exceeding the specified operating range. The

BATT

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 buf fers 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.

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.

1998 Apr 03

6

Philips Semiconductors Product specification

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SA5778Serial triple gauge driver (STGD)

Table 1. Truth Table

RUN

ÁÁ

Input

1=High

ÁÁ

0

ÁÁ

1

ÁÁ

1

ÁÁ

0

ÁÁ

0

ÁÁ

GOE

Á

Input

1=High

Á

0

Á

0

Á

1

Á

1

Á

0

Á

SwControl

ÁÁÁ

1=ON

ÁÁÁ

0

ÁÁÁ

1

ÁÁÁ

1

ÁÁÁ

1

ÁÁÁ

0

ÁÁÁ

Swbatt1,2

ÁÁ

Voltage

ÁÁ

Off

ÁÁ

V

BATT

ÁÁ

V

BATT

ÁÁ

V

BATT

ÁÁ

Off

ÁÁ

Minor Gauge Driver

БББББ

Outputs

БББББ

High Impedance

Enabled

БББББ

(output forced to zero)

БББББ

Enabled

БББББ

Enabled

БББББ

High Impedance

БББББ

Major Gauge

ÁÁÁ

Driver Outputs

ÁÁÁ

High

Impedance

High

ÁÁÁ

Impedance

ÁÁÁ

Enabled

ÁÁÁ

Enabled

ÁÁÁ

High

Impedance

ÁÁÁ

ББББББББББ

ББББББББББ

System Status

Standby mode
Start up mode, sets minor gauge driver to

zero position, and disables major gauge

ББББББББББ

driver. Load values into STGD via the serial

ББББББББББ

port.
Normal Operating mode. Periodically

update gauge data as required by the

ББББББББББ

application.
Power down sequence. Load a series of

values into the STGD to return needles to

ББББББББББ

zero before power is removed.
Returned to standby mode (same as first

row of table)

ББББББББББ

THERMAL MANAGEMENT AND POWER
DISSIPATION

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.

The highest power dissipation for a given coil driver will occur when
the coil voltage is being driven to 50% of V
dissipated by each coil driver is (V
V

BATT(VBATT

/4Rc). If the coil resistance of the two minor gauge coils

BATT

and the two coils of the major gauge all have the same resistance,
then the maximum total power dissipation of the drivers becomes
4*V

BATT(VBATT

/4Rc) or simply V

BATT(VBATT

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:

P

D=VBATT(VBATT/RC

V

OL2(VBATT–VOL2–VBE(PNP)

)+V

BATT

(0.012) +

)/R

B

Where:

= Power dissipation in watts

P

D

= Battery supply voltage in volts

V

BATT

RC = Coil resistance in ohms at ambient temperature including

any self heating effects

V

= Output low voltage of the SwCONTROL pin as specified

OL2

in the DC Characteristics

V

= The VBE drop of the external PNP transistor

BE(PNP)

RB = Resistor is series with base of external PNP transistor.
The minimum value of R

B

= V

BATTMAXIOL

. Thus the power

BATT

/2)* (V

BATT

/Rc). Much of the

=16/0.050=320 Ω

/2Rc) or

The actual value used is dependent on the current needed to

keep the PNP in saturation.

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:

R

CA

= R

(1+(0.4%/°C)*((TSH+T

CN

amb

)–25°C))

Where:

RCA = Resistance of Coil at Ambient temperature, including self
heating

= Nominal Resistance of Coil at 25°C, without self heating

R

CN

T

= Ambient temperature, °C

amb

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.

1998 Apr 03

7

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

POWER

(W)

3.0

POWER DISSIPATION FOR COIL

2.5

2.0

1.5

1.0

0.5

0.0

7.5

8

RESISTANCE IN OHMS AND OP-

ERATING BATTERY VOLTAGE

8.5

9

9.5

10

10.5

11

11.5

12

12.5

13

13.5

14

14.5

15

15.5

16

V

SWBATT

(V)

Figure 7. Power Dissipation of the STGD as a Function of Coil Resistance and Operating Voltage

16.5

125

150

175

235

325

LOAD RESISTANCE

(Ω)

17

17.5

18

SR01430

The STGD is specified to operate up to V

max. The over voltage

BATT

shutdown circuit will turn off the output buffers and the switched
battery supply when the battery voltage reaches V

OVSD.

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.

In order to determine the size of the copper foil required, both
thermal testing and thermal modeling were used. The effective

Θ

(thermal resistance, junction to ambient) was determined using

JA

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.

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 mm

2

cross

section.
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.

1998 Apr 03

8

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

50

ΘJA (°C/W)

45

ΘJA (°C/W)

40

35

30

25

0 500 1000 1500 2000 2500 3000 3500

1.4W LIMIT

PCB COPPER HEAT SINK AREA (SQ mm)

Figure 8. θJA for SO28 with 8 Fused Pins

One-sided PCB (2 oz. Copper), e = 0.9, T

45

40

1.4W LIMIT

= 105°C, P = 1.4–1.8W

amb

SR01497

1998 Apr 03

35

30

25

0 500 1000 1500 2000 2500 3000

PCB COPPER HEAT SINK AREA (SQ mm)

Two-sided PCB (2 oz. Copper), e = 0.9, T

Figure 9. θ

for SO28 with 8 Fused Pins

JA

= 105°C, P = 1.4–1.8W

amb

9

SR01498

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

Sample Calculations for Power Dissipation and
Thermal Management

Worst Case Example

The worst case example will occur when the STGD is operating at
V

BATTMAX

(105°C), and with the lowest specified coil resistance (171 ohms at
25°C). Typical coil self heating of 15°C is assumed.

Calculation of Coil resistance operating at 105°C ambient.

Calculation of STGD power dissipation at 16 volt operation.

Required board area and Junction Temperature calculation

The maximum junction temperature desired is 150°C. The
permissible temperature rise and required Θ
as:

Where; ∆T = Temperature rise in °C

(16V , in the highest specified ambient temperature

R

= RCN (1+(0.4%W/°C)*((TSH+T

CA

amb

)–25°C))
= 171 x(1+(0.4%((15+105)–25)))
= 236 Ohms at T

PD= V

BATT

(V

+V

OL2

(V

BATT

BATT/RC

=105°C, with 15°C of self heating.

amb

– V

)+ V

OL2

– V

(0.012)

BATT

BE(PNP)

) / R

L

= 16(16/236)+16(0.012)+1.5(16–1.5–0.5)/320
= 1.085+0.192+0.066 Watts
= 1.34 Watts

JA

∆T = T

j–Tamb

ΘJA = ∆T/P

D

PD = Power dissipation
Tj = Junction Temperature

= Ambient Temperature

T

amb

∆T = TJ–T

= 150 – 105 = 45°C

amb

ΘJA = ∆T/PD=55°C/1.34 watts = 33°C/W.

may be calculated

From Figure 8, the copper area required, using a single sided board,
to keep the junction temperature within limits is approximately
2200 mm

2

. Figure 9 shows 1200 mm2 is required on each side of a

double-sided board.
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.

Serial Interface

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 S
the rising edge of S

. Major gauge data is loaded first, starting

CLK

with the most significant bit, followed by minor gauge 1 data then
minor gauge 2 data.

, while input data is captured on

CLK

1998 Apr 03

DATA

DATA

t

CYC

t

CF

t

S

CLK

CS

IN

OUT

CSH

t

SU

12930

D29 D1 D0*

t

DR

S4 D1* D0*

t

CR

30 CLOCK CYCLES

t

HD

t

CSL

t

SCLKL

t

DF

t

SCLKH

SR01499

Figure 10. Serial Interface Timing

10

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

MINOR GAUGE 2 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

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

Figure 11. Internal Shift Register

15

DATA OUTDATA IN

MSBMSBMSB LSBLSBLSB

SR01123

COS

10

5

0

0 127 255 383 511 639 767 895 1023

–5

DIFFERENTIAL OUTPUT VOLTAGE

–10

–15

Figure 12. Major Gauge Output Voltages (V

SIN

INPUT CODE

SWBATT

= 14V)

SR01500

1998 Apr 03

11

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

14.00

12.00

10.00

8.00

6.00

4.00

2.00

0.00

–2.00

C+ – C– (VOLTS)

–4.00

–6.00

–8.00

–10.00

–12.00

–14.00

Figure 13. Typical Minor Gauge Output Voltage vs. Input Code (V

31 63 95 127 159 191 223 255 287 319

INPUT CODE

SL00462

= 14V)

SWBATT

–0.744 x V

0.5 x V

SWBATT

+56°–56°

SWBATT

TOTAL SPAN = 112.15° STEP SIZE = 0.35°

0.744 x V

SWBATT

IDEAL ANGLE(DEGREE)=CODE/319*2* ArcTan (0.744/0.5)–ArcTan(0.744/0.5)

Figure 14. Minor Gauge Total Span

ASSUMING CODE 0 IS 0°:

CODE

31
63

95
127
159
191
223
255
287
319

POSITION

0

–56.097
–45.194
–33.940
–22.685
–11.430

–0.176

11.079

22.333

33.588

44.843

56.097

SR01501

1998 Apr 03

12

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

120

100

80

60

ANGLE (DEGREES)

40

20

0

01531 637995111127143

Figure 15. Meter Position (degrees) vs. Input Code for Minor Gauges

159 175 191 207 223 239 255 271 287 30341

INPUT CODE

319

SL00464

1998 Apr 03

13

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

SO28: plastic small outline package; 28 leads; body width 7.5mm SOT136-1

1998 Apr 03

14

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

NOTES

1998 Apr 03

15

Philips Semiconductors Product specification

SA5778Serial triple gauge driver (STGD)

Data sheet status

Data sheet
status

Objective
specification

Preliminary
specification

Product
specification

Product
status

Development

Qualification

Production

Definition

This data sheet contains the design target or goal specifications for product development.
Specification may change in any manner without notice.

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.

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]

[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.

Philips Semiconductors
811 East Arques Avenue
P.O. Box 3409
Sunnyvale, California 94088–3409
Telephone [phone]

 Copyright Philips Electronics North America Corporation 1998

All rights reserved. Printed in U.S.A.

Date of release: 04–98

Document order number: 9397 750 03715

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1998 Apr 03

16