SA5778D NXP Semiconductors, SA5778D Datasheet - Page 7

• Manufacturer Part Number: SA5778D
• Manufacturer: NXP Semiconductors

Specifications of SA5778D

• Operating Temperature (max): 105C
• Operating Temperature (min): -40C
• Pin Count: 28
• Mounting: Surface Mount
• Package Type: SO
• Screening Level: Industrial
• Lead Free Status / Rohs Status: Compliant

Philips Semiconductors
Table 1. Truth Table
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
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
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:
Where:
1998 Apr 03
BATT
1=High
Serial triple gauge driver (STGD)
Input
RUN
P
P
V
R
V
V
R
The minimum value of R
BATT
D
D
BATT
C
OL2
BE(PNP)
B
0
1
1
0
0
(V
=V
V
= Power dissipation in watts
any self heating effects
in the DC Characteristics
= Resistor is series with base of external PNP transistor.
= Coil resistance in ohms at ambient temperature including
(V
OL2
BATT
BATT
= Output low voltage of the SwCONTROL pin as specified
= Battery supply voltage in volts
BATT
(V
= The V
/4Rc). If the coil resistance of the two minor gauge coils
(V
1=High
BATT
Input
/4Rc) or simply V
GOE
BATT
0
0
1
1
0
–V
BE
/R
OL2
C
drop of the external PNP transistor
)+V
–V
SwControl
BATT
BE(PNP)
B
1=ON
= V
0
1
1
1
0
(0.012) +
BATT
BATTMAX
BATT
)/R
(V
B
/2)* (V
BATT
Swbatt1,2
Voltage
I
OL
BATT
V
V
V
/Rc). Much of the
Off
BATT
BATT
BATT
Off
=16/0.050=320
BATT
. Thus the power
/2Rc) or
(output forced to zero)
Minor Gauge Driver
High Impedance
High Impedance
Outputs
Enabled
Enabled
Enabled
7
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:
Where:
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.
The actual value used is dependent on the current needed to
All gauges at 45 to a quadrant axis, as this is the highest
R
R
heating
R
T
T
0.4%/ C = Resistance increase coefficient for copper
Driver Outputs
amb
SH
CA
CA
CN
Major Gauge
Impedance
Impedance
Impedance
keep the PNP in saturation.
internal power dissipation position.
= Self heating of coil, C
Enabled
Enabled
= Resistance of Coil at Ambient temperature, including self
= R
= Nominal Resistance of Coil at 25 C, without self heating
= Ambient temperature, C
High
High
High
CN
(1+(0.4%/ C)*((T
Standby mode
Start up mode, sets minor gauge driver to
zero position, and disables major gauge
driver. Load values into STGD via the serial
port.
Normal Operating mode. Periodically
update gauge data as required by the
application.
Power down sequence. Load a series of
values into the STGD to return needles to
zero before power is removed.
Returned to standby mode (same as first
row of table)
SH
+T
System Status
amb
)–25 C))
Product specification
SA5778