TYPICAL APPLICATION
fault status pin allows reduced diagnosis, as illustrated in
table 3.
DIAGNOSIS WITHOUT MCU
When any fault appears (over-current, open load…), a full
diagnosis can be reported via the SPI. Without an MCU, the
Table 3. Diagnosis without SPI
IN[x] level
HS[x] level
FS level
Latched
H
L
H
L
L
L
L
L
L
L
L
L
H
H
Z
H
H
H
L
Normal operation
Over-temperature
Under-voltage
N/A
L
YES
YES
NO
H
L
L
L
H
L
L
H
L
Over-voltage
H
L
H
L
Over-current
YES
NO
H
L
L
Short-circuit to VPWR
Open load
H
L
H
L
NO
H
H
H : High Level, L : Low Level, Z : High-impedance, potential depends on the external circuit
We can note that it is not possible to distinguish over
CONCLUSION
temperature, over-current, under-voltage, and over-voltage.
Nevertheless, Open load and short-circuit to VPWR fault can
Although the MC33874 is not fully functional without a
microcontroller to control and program it, standalone
functioning is safe because all protections are available.
Diagnosis is limited, but the fault status pin will report any
malfunction.
be singled out. All protections are reported to Fault status pin
(FS), Open load and short-circuit to VPWR are reported only if
the Output is OFF. If the fault is latched, the output must be
turned OFF then ON to disable the fault.
This is a good way to evaluate the main electrical
MC33874 features. Some simplified applications can also
use the MC33874 switch without an MCU to drive a high
power load with full protection.
33874
Analog Integrated Circuit Device Data
Freescale Semiconductor
30
FREESCALE [ Freescale ]
