MC33298DW Freescale Semiconductor, MC33298DW Datasheet - Page 20

• Manufacturer Part Number: MC33298DW
• Description: IC SWITCH SERIAL OCTAL 24-SOIC
• Manufacturer: Freescale Semiconductor
• Type: Low Sider

Specifications of MC33298DW

• Input Type: SPI
• Number Of Outputs: 8
• On-state Resistance: 350 mOhm
• Current - Output / Channel: 1A
• Current - Peak Output: 4A
• Voltage - Supply: 9 V ~ 26.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

output voltage is less than the Output Threshold Voltage
(V
as switches, during normal operation, each MOSFET output
should either be completely turned ON or OFF. By design,
the threshold voltage was selected to be between the ON and
OFF voltage of the MOSFET. During normal operation, the
ON state V
threshold voltage and the OFF state V
than the threshold voltage. This design approach provides
using the same threshold comparator for Output Open Load
Detect in the OFF state and Short-circuit Detect in the ON
state. See
Detect circuit. With V
of less than 3.0V will be detected as an Output OFF Open
Load Fault while voltages greater than 4.0V will not be
detected as a fault.
50µA, illustrated in
and ground. This current source prevents the output from
floating up to V
bond failure. The internal comparator compares the drain
voltage with a reference voltage, V
the output voltage is less than this reference voltage, the
33298 will declare the condition to be an open load fault.
resistance (R
normal operation can be located using the following equation.
open load fault reporting is (using Ohm’s Law) equal to 92kΩ
or less.
a false output OFF Open Load Fault may be triggered. To
prevent this false fault from being reported an internal fault
filter in the range of 25 to 100µs is incorporated. The duration
in which a false fault may be reported is a function of the load
impedance (R
well as the supply voltage (V
triggers a built-in fault delay timer which must time-out (25 or
100µs) before the fault comparator is enabled to detect at
faulted threshold. The circuit automatically returns to normal
20
33298
FUNCTIONAL DESCRIPTION
FAULT LOGIC OPERATION
THRES
An Output OFF Open Load Fault is indicates when the
The 33298 has an internal pull-down current source of
During steady-state operation, the minimum load
Therefore, the load resistance necessary to prevent false
During output switching, especially with capacitive loads,
) of 0.6 to 0.8 x V
Figure 19. Output OFF Open Load Fault
Low = Fault
Figure 20
DS
L
L
voltage of the MOSFET is less than the
) required to prevent false fault reporting during
+
–
,C
PWR
2.5 to 3.5V
L
V
,L
THRES
Figure 19
if there is an open load or internal wire
L
for an understanding of the Short-circuit
DD
), R
= 5.0V, an OFF state output voltage
DD
DS(ON)
33298
MOSFET OFF
. Since the 33298 outputs function
PWR
between the MOSFET drain
, and C
). The rising edge of CS
THRES
OUT
DS
50µA
(0.6 to 0.8 x V
voltage is greater
of the MOSFET as
R
L
Output
V
PWR
DD
). If
operation once the condition causing the Open Load Fault is
removed.
SHORTED LOAD FAULT
output being shorted directly to supply, or an output
experiencing a current greater than the current limit.
during load short conditions providing system protection.
They are:
in their output providing robust independent output operation.
the output drain current. An over-current condition causes the
gate control circuitry to reduce the gate-to-source voltage
imposed on the output MOSFET, re-establishing the load
current in compliance with current limit (3.0 to 6.0A) range.
Time required for the current limit circuitry to act is less than
20µs. Therefore, currents higher than 3.0 to 6.0A will never
be seen for more than 20µs (a typical duration is 10µs). If the
current of an output attempts to exceed the predetermined
limit of 3.0 to 6.0A (4.0A nominal), the V
exceed the V
will be tripped, illustrated in
shut down immediately, or continue to operate in an analog
current limited mode until either the short-circuit (over-
1. The output current of the device is monitored in an
2. The output current of the device is sensed by
3. The output thermal limit of the device is sensed, and
A short load, or over-current fault can be caused by any
There are three safety circuits progressively in operation
Each of the three protection mechanisms are incorporated
The analog current limit circuit is always active, monitoring
The status of SFPD determines whether the 33298 will
analog fashion using a SENSEFET™ approach and
current limited.
monitoring the MOSFET drain voltage.
when attained, causes only the specific faulted output
to be latched OFF, allowing all remaining outputs to
operate normally.
Analog
Figure 20. Short Circuit Detect and
THRES
Analog Current Limiting Circuit
+
–
Digital
High = Fault
V REF
voltage and the over-current comparator
33298
Analog Integrated Circuit Device Data
2.5 to 3.5V
+
–
V
THRES
Figure
Freescale Semiconductor
20.
MOSFET ON
DS
voltage will
R
Output
L
V
PWR