FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
temperature of the output driver to determine the fault. Both
methods may be selected or used individually. The following
table provides an explanation of operation during fault
condition.
PARALLEL OUTPUT, PX PIN ENABLE COMMAND
The Parallel Output command allows the user to parallel
output for increased current capability and enables control of
the PX input pin.
The low duty cycle used for the timer protection scheme is
set by the fault timer used to detect the short circuit. For short
circuits detected based on the output voltage exceeding the
fault detection voltage threshold, the outputs will be turned off
for the duration of the refresh timer (typically 10ms) and
turned on for the duration of the on-state short circuit fault
timer (typically 500µs). For short circuits detected based on
the output current exceeding the output current limit, the
outputs will be turned off for the duration of the refresh timer
(typically 10 ms) and turned on for the duration of the current
limit fault timer (typically 50µs).
A logic 0 in the Parallel Output Command provides
individual control. Logic 1 commands outputs to operate in
parallel. For example, with bit 4 in the Parallel Output
command a logic 1, outputs 1 & 2 are controlled together
With the outputs paralleled, and the P1 pin enabled, a logic
1 on SPI bit 0 or SPI bit 1 will command both outputs on.
Similarly a logic 1 on the P1 pin will command both outputs
on.
PX pin Enable bit 0 through bit 3 enables or disables the
P1, P3, P5, P7 pins respectively. A logic 0 in the SPI word will
enable the PX input pin, while logic 1 in the SPI word will
disable the PX input pin. Default state is with the PX input
pins enabled.
For off-state open load faults with retry timer enabled, the
off-open fault is released and re-detected every 1-2 retry
timer periods. Retry timer for 1-2, 3-4, 5-6, and 7-8 are out of
phase and may report a load present, if the OSS read
command CS is issued after the release, and before the re-
detection (~500µs) of the off-state open load fault.
When paralleling output 1 & 2 the current limit is
maintained at 4.0 to 6.0A. Parallel current limit for drivers
3&4, 5&6, 7&8 is increased to a range of 2.0 to 4.0A.
Using a MOSFET as output switches allows the
connection of paired outputs. The RDS(ON) of MOSFET
devices have inherent positive temperature coefficient
providing balanced current sharing between outputs without
destructive operation. This mode of operation may be
desirable in the event the application requires lower power
dissipation or the added capability of switching higher
currents. Performance of parallel operation results in a
corresponding decrease in RDS(ON), while the Output Current
Limit increases correspondingly. Output OFF Open Load
Detect current may increase based on how the Output OFF
Open Load Detect is programmed.
Table 13. TLim/Timer Control
Fault
Timer
Bit
Shutdn
Retry Bit
TLIM
Bit
Operation During Short Fault
Timer only, Outputs will retry on
period
1
0
X
OUT1-8 = ~500us for short
circuit faults, and 50us for current
limit faults ON, ~10ms OFF.
TLim only, Outputs will retry on
TLim hysteresis.
1
1
1
1
0
1
Table 14. And/Or/SPI/Parallel Control
Timer and TLim, Outputs will
retry on period and driver
temperature below threshold.
Parallel PX Pin
AND/
OR Bit Bit 1
SPI
SPI
Bit 0
Output
1&2
PX Pin
En Bit
En Bit
OUT1-8 = ~500us ON, ~10ms
OFF
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
1
1
1
1
1
X
X
X
X
0
0
0
0
0
X
1
1
1
X
0
0
1
1
0
0
1
1
X
0
0
1
1
0
1
0
1
0
1
0
1
X
0
1
0
1
OFF
ON
X
Timer only, Outputs will not retry
on period
0
0
X
X
ON
OUT1-8 = ~500us ON, OFF
X
ON
TLim only, Outputs will not retry
on TLim hysteresis.
0
0
1
1
0
1
1(or)
1(or)
1(or)
1(or)
0(and)
0(and)
0(and)
0(and)
0(and)
OFF
ON
Timer and TLim, Outputs will not
retry on period or TLim.
ON
OUT1-8 = ~500us ON, OFF
ON
All OSS outputs have a current limit control loop. Current
limit is always active in Normal Mode. Current limit for OUT1
and OUT2 is 4.0 to 6.0A. Current limit for OUT3 through
OUT8 is 1.0 to 2.0A.
OFF
OFF
ON
ON
ON
33800
Analog Integrated Circuit Device Data
Freescale Semiconductor
26
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