mc33291l Freescale Semiconductor, Inc, mc33291l Datasheet - Page 20

• Manufacturer Part Number: mc33291l
• Description: Eight-output Switch With Serial Peripheral Interface I/o
• Manufacturer: Freescale Semiconductor, Inc

The eight output-off open-load faults are therefore most
easily detected.
logic low, when calling for the output to be programmed on,
the next word command entered into the corresponding bit
returns with a logic high on SO. An output overcurrent fault
would be indicated. An overcurrent fault is always reported by
the SO output and is independent of the logic state existing
on the SFPD pin. When the SFPD pin is in a logic high state,
an overcurrent condition will be reported on the SO pin.
However, limiting output current is in effect and the output is
permitted to operate if the overcurrent condition does not
drive output into an overtemperature fault. An
overtemperature fault will shut down the specific output
effected for the duration of the overtemperature condition.
Turning the effected output switches OFF and waiting for
some time to allow the output to cool down should make
these types of faults go away. Soft overcurrent faults can
sometimes be determined over hard short faults and
overtemperature faults by observing the time required for the
device to recover. However, in general overcurrent and
overtemperature faults cannot be differentiated in normal
application usage.
faults can be detected with only one (SO) pin being used for
fault status reporting.
will immediately be turned OFF and remain latched OFF. A
new command word is required to turn the outputs back ON
following an overvoltage condition.
Output Voltage Clamping
clamp to provide fast turn-off and transient protection of the
output. Each clamp independently limits the drain-to-source
voltage to 53 V at drain currents of 0.5 A and keeps the
output transistors from avalanching by causing the transient
energy to be dissipated in the linear mode (see
The total energy clamped (E
multiplying the current area under the current curve (I
the clamp voltage (V
(t).
non-repetitive method at 0.5 A, indicates the maximum
energy to be 50 mJ at 150°C junction temperature per output.
20
33291L
FUNCTIONAL DESCRIPTION
If for a specific output the initial SI command bit were a
Overcurrent and overtemperature faults are often related.
An advantage of the synchronous serial output is multiple
If V
Each output of the 33291L incorporates an internal voltage
Characterization of the output clamps, using a single pulse
PWR
experiences an overvoltage condition, all outputs
CL
) times the duration the clamp is active
J
) can be calculated by
Figure
A
) times
20).
THERMAL CHARACTERIZATION
THERMAL MODEL
generate negligible power. In contrast, the output transistors
take up most of the die area and are the primary contributors
of power generation. The thermal model illustrated in
Figure
on a typical PC board. The model is accurate for both steady
state and transient thermal conditions. The components R
through R
the silicon die for transistor outputs 0 through 7, while C
through C
capacitance of the silicone die translator outputs and plastic.
The device area and die thickness determine the values of
these specific components.
mounting flag to the outside environment is represented by
the terms R
of leads and the PC board make up the steady state package
thermal resistance, R
package is made up of the combined capacitance of the flag
and the PC board. The mode compound was not modeled as
a specific component but it is factored into the other overall
component values.
ambient temperature the device and PC board are subjected
to. The I
dissipation and is calculated by totalling the power dissipation
of each individual output transistor. This is easily
accomplished by knowing R
individual outputs.
experienced with this thermal model. Tests indicate the
model accuracy to have less than 10 percent error. Output
interaction with an adjacent output is believed to be the main
contributor to the thermal inaccuracy. Tests indicate little or
no detectable thermal effects caused by distant output
transistors isolated by one or more other outputs. Tests were
Drain-to-Source ON
Drain-to-Source Clamp
Drain Current
Voltage (V
Voltage (VCL = 65 V)
Logic functions take up a very small area of the die and
The thermal impedance of the package from the internal
The battery voltage in the thermal model represents the
Very satisfactory steady state and transient results are
(ID = 0.5 A)
21, page 21, was developed for the 33291L mounted
PWR
GND
d7
d7
DS(ON)
Figure 20. Output Voltage Clamping
pkg
represent the steady state thermal resistance of
represent the corresponding thermal
current source represents the total power
and C
)
pkg
pkg
Analog Integrated Circuit Device Data
. The steady state thermal resistance
. The thermal capacitance of the
Area (I A )
Current
DS(ON)
and load current of the
Freescale Semiconductor
Drain Voltage
(E
Clamp Energy
J
= I
A
x V
CL
VPWR
Time
x t)
d0
d0