Datasheet

LTC3880/LTC3880-1
27
3880fc
For more information www.linear.com/LTC3880
OPERATION
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 100ms
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 temperature has dropped to 120°C.
Temperature is measured by the ADC. Internal tempera
-
ture faults cannot be ignored. Internal temperature limits
cannot be adjusted by the user.
See T
able 9.
Overtemperature and Undertemperature
Fault Response—Externals
Two external temperature sensors can be used to sense
critical cir
cuit elements like inductors and power MOSFETs.
The OT_FAULT_RESPONSE and UT_FAULT_RESPOSE
commands are used to determine the appropriate response
to an overtemperature and undertemperature condition,
respectively. If no external sense elements are used
(not recommended) set the UT_FAULT_RESPONSE to
ignore and set the UT_FAUL
T_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.
RESPONSES TO EXTERNAL FAULTS
When either GPIOn pin is pulled low, the OTHER bit is set
in the STATUS_WORD command, the appropriate bit is set
in the STATUS_MFR_SPECIFC command, and the ALERT
pin is pulled low. Responses are not deglitched. Each chan
-
nel can be configured to ignore or shut down then retry
in response to its
GPIO
n pin going low by modifying the
MFR_GPIO_RESPONSE command. To avoid the ALERT
pin asserting low when GPIO is pulled low, assert bit 1 of
MFR_CHAN_CONFIG_LTC3880.
FAULT LOGGING
The LTC3880 has fault logging capability. Data is logged
into memory in the order shown in Table 11. The data to
be stored in the fault log is being continuously stored in
internal volatile memory. When a fault event occurs, the
recording into internal volatile memory is halted, the fault
log information is available from the MFR_FAULT_LOG
command, and the contents of the internal memory are
copied into NVM. Fault logging is allowed at temperatures
above 85°C; however, retention of 10 years is not guaran
-
teed. When the die temperature exceeds 130°C the fault
logging is delayed until the die temperature drops below
120°C. After the fault condition that created the fault log
event has been removed, clear the fault before the fault