Datasheet

sampled by the internal power measurement circuitry and
used to calculate PEAK PIN.
The Identification Information can be obtained by clicking the
Update ID Information button.
The rest of this page is used to monitor and diagnose warning
and fault conditions. The SMBA interrupt will indicate if a
warning or fault has occurred and if the output voltage is within
specifications. It is always active and there is no need to click
an Update button to change their state. The LM25056 does
not have a PGOOD indicator and is not used in this device.
Clicking the Update Status button under the Register Opera-
tion Control heading will update the bits in all of the registers
under the Status section as well as the telemetry in the
BLACK_BOX_READ. Clicking the CLEAR_FAULTS will re-
set all warning and fault bits and issue an Update Status. If
the warning and/or fault condition has been remedied, the bits
will reset. If the warning and/or fault condition still exists, the
registers will be updated within a millisecond and thus will
appear to never have been cleared. The STATUS_WORD,
STATUS_INPUT, STATUS_CML and DIAGNOSTIC_WORD
registers operate in a cumulative way. That is, these registers
display any and all warnings and errors that have occurred
since the last CLEAR_FAULTS command was issued.
The telemetry and DIAGNOSTIC_WORD that are part of the
BLACK_BOX_READ are also updated by clicking the Update
Status button. These telemetry parameters and bits are
latched at the moment the SMBA signal was asserted. They
are not reset or cleared by the CLEAR_FAULTS command
but rather they are re-armed, or readied, to be over-written
with new values at the onset of the next SMBA signal asser-
tion. Note that these telemetry fields and this register are not
cumulative. That is, they can only be updated once after the
CLEAR_FAULTS command is issued, and it will be at the first
occurrence of the SMBA assertion following the
CLEAR_FAULTS. This allows the user to determine device
conditions at the first occurrence of the SMBA assertion.
Shutdown
With the circuit in normal operation, the LM25056 can be
shutdown by grounding the ENABLE pin.
External VDD
The LM25056 VDD can be powered from an external source
to maintain some telemetry readings if the VIN fails. On the
evaluation board, a connection of VDDX to 5V can be used
to power the VDD line and maintain telemetry readings for
VIN and temperature. The VDDX supplies power through a
Schottky diode and a large capacitor.
Note that with an external VDD connected to the VDDX line,
the LM25056 cannot be put into a low power mode with the
ENABLE pin. In this case, simply connect the ENABLE to
VDDX and lower this line down to disable the part.
Board Layout and Probing Cautions
Refer to the product datasheet for detailed layout guidelines.
For most applications the layout of this evaluation module as
detailed in the PC Board Layout section of this document
should be sufficient to provide a working solution with accu-
rate telemetry. The following should be kept in mind when the
board is powered:
1.
Use caution when probing the circuit to prevent injury as
well as possible damage to the circuit.
2.
At larger load current (>15A), the wire size and length
used to connect the power source and the load may
become very important. The wires connecting this
evaluation board to the power source should be twisted
together to minimize inductance in those leads. The
same applies for the wires connecting this board to the
load. This recommendation is made in order to minimize
high voltage transients from occurring when the load
current is shut off.
3.
A 15V TVS diode located as close as possible to the
LM25056 VIN and GND pins provides the critical function
of clamping inevitable input voltage overshoots when the
pass MOSFET turns off.
4.
An analog signal ground plane is used local to the
LM25056 and is connected to the PCB power ground
planes at a single point.
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