Datasheet

LTC3883/LTC3883-1
26
3883fa
For more information www.linear.com/LTC3883
OPERATION
The overcurrent fault processing circuitry can execute the
following behaviors:
n
Current Limit Indefinitely
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
The overcurrent responses can be deglitched in increments
of (0-7) • 16ms. See Table 7
RESPONSES TO TIMING FAULTS
TON_MAX_FAULT_LIMIT is the time allowed for V
OUT
to
rise and settle at start-up. The TON_MAX_FAULT_LIMIT
condition is predicated upon detection of the VOUT_UV_
FAULT_LIMIT as the output is undergoing a SOFT_START
sequence. The TON_MAX_FAULT_LIMIT time is started
after TON_DELAY has been reached and a SOFT_START
sequence is started. The resolution of the TON_MAX_
FAULT_LIMIT is 10µs. If the VOUT_UV_FAULT_LIMIT
is not reached within the TON_MAX_FAULT_LIMIT time,
the response of this fault is determined by the value of
the TON_MAX_FAULT_RESPONSE command value. This
response may be one of the following:
n
Ignore
n
Shut Down (Stop Switching) Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
This fault response is not deglitched. A value of 0 in
TON_MAX
_FAULT_LIMIT means the fault is ignored. The
TON_MAX_FAULT_LIMIT should be set longer than the
TON_RISE time. It is recommended TON_MAX_FAULT_
LIMIT always be set to a non-zero value, otherwise the
output may never come up and no flag will be set to the
user.
See Table 9.
RESPONSES TO V
IN
OV FAULTS
V
IN
overvoltage is measured with the MUX’d ADC; there-
fore, the response is naturally deglitched by the 120ms
typical
response time of the ADC. The fault responses are:
n
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
See Table 9.
RESPONSES TO OT/UT FAULTS
Overtemperature Fault Response—Internal
An internal temperature sensor protects against NVM
damage. Above 85°C, no writes to NVM are recommended.
Above 130°C, the part disables the NVM and does not re-
enable until the internal temperature has dropped to 125°C.
The LTC3883 sets bit 7 of the STATUS_TEMPERATURE
command (‘OT Warn’) above 130°C, and this bit cannot
be cleared until the internal temperature has dropped to
125°C. Above 160°C, the LTC3883 disables the PWM and
does not re-enable the PWM until
the internal temperature
has dropped to 150°C. The part sets bit 6 of the STATUS_
TEMPERATURE command
(‘
OT Fault’) above 160°C, and
this bit cannot be cleared until the internal temperature has
dropped to 150°C. Temperature is measured by the ADC.
Internal temperature faults cannot be ignored. Internal
temperature limits cannot be adjusted by the user.
See Table 9.
Overtemperature and Undertemperature
Fault Response—Externals
An external temperature sensors can be used to sense
critical circuit elements like the inductor and power
MOSFETs. The OT_FAULT_RESPONSE and UT_FAULT_
RESPOSE commands
are used to determine the appropri-
ate response t
o an overtemperature and undertemperature
condition, respectively. If no external sense element is used
(not recommended
)
set the UT_FAULT_RESPONSE to
ignore and set the UT_FAULT_LIMIT to –275°C.
The fault responses are:
n
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
See Table 9.