Datasheet

LTC2928
15
2928f
Fault Detection
The LTC2928 has sophisticated fault detection circuitry
which can detect:
• Stalled supplies (with power good timer enabled)
during sequencing
• Under or overvoltage supplies
• System controller command errors
• Externally commanded faults
If any of the above faults are detected, the LTC2928
immediately pulls the EN1 through EN4 outputs low,
turning off all enabled supplies.
In order to clear the fault condition within the LTC2928,
the following conditions must exist:
• All sequenced supplies must be below their sequence-
down thresholds
• The ON input must be below 0.97V
• The F LT pin must be externally released
Sequencing Faults
The LTC2928 keeps track of power supplies that need to
exceed their sequencing thresholds within the configured
power good time during the sequence-up and sequence-
down phases. Should any supply fail this test a sequence
fault is generated. All enable outputs and F LT are pulled low.
System Controller Command Faults
After the sequence-up phase has begun (ON input high),
the ON input must remain above 1V until DONE pulls
low (sequence-up complete). Pulling ON low before the
sequence-up process is complete is considered a command
fault. All enable outputs and F LT are pulled low.
Similarly, after the sequence-down phase has begun (ON
input low), the ON input must remain below 0.97V until
DONE pulls high (sequence-down complete). Pulling ON
high before the sequence-down process is complete is
considered a command fault. All enable outputs and F LT
are pulled low.
Reset Faults
Use the MS1 and MS2 configuration pins to select whether
or not the system should fault if any monitored input falls
below its undervoltage threshold. A reset fault may only
occur after the LTC2928 comes out of reset for the first
time after sequencing. All enable outputs and F LT are
pulled low.
External Faults
An external fault is generated by pulling the F LT pin low.
Tie the OV pin to F LT to generate overvoltage faults. In
applications using multiple LTC2928s, tie all the F LT pins
together to ensure proper re-sequencing. Upon detecting
an external fault, all enable outputs are pulled low.
Fault Reporting Map
For diagnostic purposes, fault information is latched to
the comparator outputs after a fault. The table below
provides a map to the available fault information. The fault
information remains latched until the LTC2928 completes
the next sequence-up operation.
Table 5. Fault Reporting
Fault Codes
Fault Type CMP1 CMP2
Sequence Fault Low Low
Reset Fault Low High
Command Fault High Low
External Fault High High
Fault Channel CMP3 CMP4
1 Low Low
2 Low High
3 High Low
4 High High
Should multiple faults occur simultaneously, the reported
fault is given priority according to the following order:
1) Sequence Fault
2) External Fault
3) Reset Fault
4) Command Fault (channel code is meaningless)
APPLICATIO S I FOR ATIO
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