mc33879a Freescale Semiconductor, Inc, mc33879a Datasheet - Page 20

• Manufacturer Part Number: mc33879a
• Description: Configurable Octal Serial Switch With Open Load Detect Current Disable
• Manufacturer: Freescale Semiconductor, Inc

to-source voltage is less than the output threshold voltage
(V
the load open in the OFF state when the output drain-to-
source voltage is less than V
connected from drain to source of the output MOSFET. The
current source may be programmed on or off via SPI. The
Power-ON Reset state for the current source is “off” and must
be enabled via SPI. To achieve low Sleep mode quiescent
currents, the Open Load Detection Current source of each
driver is switched off when V
a false output OFF open load fault may be triggered. To
prevent this false fault from being reported, an internal fault
filter of 100 Ps to 300 Ps is incorporated. A false fault
reporting is a function of the load impedance, R
of the MOSFET, as well as the supply voltage, V
rising edge of
timer will time out before the fault comparator is enabled and
the fault is detected. Once the condition causing the open
load fault is removed, the device will resume normal
operation. The open load fault, however, will be latched in the
output DO register for the MCU to read.
SHORTED LOAD FAULT
output being shorted directly to supply, or an output
experiencing a current greater than the current limit.
during load short conditions that provide system protection:
UNDERVOLTAGE SHUTDOWN
shutdown of all outputs. The V
between 0.8 V and 3.0 V. V
between 3.0 V and 5.0 V. When the supplies fall below their
respective thresholds, all outputs are turned OFF. As both
supplies returns to normal levels, internal logic is reset and
the device resumes normal operation.
20
33879
FUNCTIONAL DESCRIPTION
DEVICE OPERATION
OUT(
1. The device’s output current is monitored in an analog
2. The device’s output thermal limit is sensed and when
An output OFF open load fault is indicated when the drain-
This device has an internal 80 PA current source
During output switching, especially with capacitive loads,
A shorted load (overcurrent) fault can be caused by any
There are two safety circuits progressively in operation
An undervoltage condition on V
fashion using SENSEFET approach and current
limited.
attained causes only the specific faulted output to shut
down. The output will remain off until cooled. The
device will then reassert the output automatically. The
cycle will continue until fault is removed or the
command bit instructs the output off. Shorted load
faults will be reported properly through SPI regardless
of Open Load Detection Current enable bits.
flt-th
)
) of 2.5 V to 4.0 V. Hence, the 33879 will declare
CS
triggers the built-in fault delay timer. The
PWR
DD
OUT(flt-th)
DD
or EN is removed.
undervoltage threshold is
DD
undervoltage threshold is
or V
.
PWR
will result in the
DS(ON)
PWR
. The
, C
OUT
OUTPUT VOLTAGE CLAMP
clamp to provide fast turn-off and transient protection of each
output. Each clamp independently limits the drain-to-source
voltage to 45 V for low-side drive configurations and -20 V for
high-side drive configurations. The total energy clamped (E
can be calculated by multiplying the current area under the
current curve (I
Figure
non-repetitive method at 0.35 A, indicates the maximum
energy per output to be 50 mJ at 150
SPI CONFIGURATIONS
with other devices in the Octal Serial Switch (OSS) family.
This device may be used in serial SPI or parallel SPI with the
33298 and 33291. Different SPI configurations may be
provided. For more information, contact Freescale Analog
Products Division or local Freescale representative.
REVERSE BATTERY
protection on the V
substrate diode. During the reverse battery condition, current
will flow through the load via the substrate diode. Under this
circumstance, relays may energize and lamps will turn on.
Where load reverse battery protection is desired, a reverse
battery blocking diode must be placed in series with the load.
Drain-to-Source ON
Voltage (V
Drain-to-Source ON
Voltage (V
Each output of the 33879 incorporates an internal voltage
Characterization of the output clamps, using a single pulse
The SPI configuration on the 33879 device is consistent
The 33879 has been designed with reverse battery
All outputs consist of a power MOSFET with an integral
Drain-to-Source Clamp
Voltage (V CL = 45 V)
Drain Current
(I
Source Current
Source Clamp Voltage
(V
18).
D
CL
(I S = 0.3 A)
= 0.3 A)
DS(ON)
DS(ON)
= -15 V)
Figure 18. Output Voltage Clamping
GND
GND
)
)
A
VS
) times the clamp voltage (V
PWR
Analog Integrated Circuit Device Data
pin.
Current
Current
Area (I A )
Area (I A )
Freescale Semiconductor
°
C junction temperature.
Drain Voltage
Source Voltage
(E
Clamp Energy
(E
Clamp Energy
J
J
= I
= I
CL
A
) (see
A
x V
x V
CL
CL
Time
BAT
Time
)
)
J
)