Output Undervoltage Response; Peak Output Overcurrent Fault Response; Responses To Timing Faults; Responses To Vin Ov Faults - Analog Devices Linear LTM 4700 User Manual

OPERATION

Output Undervoltage Response

The response to an undervoltage comparator output can
be the following:
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
Time Interval Specified in MFR_RETRY_DELAY.
The UV responses can be deglitched. See Table 15.

Peak Output Overcurrent Fault Response

Due to the current mode control algorithm, peak output
current across the inductor is always limited on a cycle-by-
cycle basis. The value of the peak current limit is specified
in Electrical Characteristics table. The current limit circuit
operates by limiting the COMPn maximum voltage. Since
internal DCR sensing is used, the COMPn maximum voltage
has a temperature dependency directly proportional to the
TC of the DCR of the inductor. The LTM4700 automatically
monitors the external temperature sensors and modifies
the maximum allowed COMPn to compensate for this
term. The IOUT_OC_FAULT_LIMIT section provides data
points for I Limiting on page 89.
OUT
The overcurrent fault processing circuitry can execute the
following behaviors:
Current Limit Indefinitely
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
Time Interval Specified in MFR_RETRY_DELAY.
The overcurrent responses can be deglitched in increments
of (0-7) • 16ms. See Table 16

RESPONSES TO TIMING FAULTS

TON_MAX_FAULT_LIMIT is the time allowed for V
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:
Ignore
n
Shut Down (Stop Switching) Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
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 17.
RESPONSES TO V
V overvoltage is measured with the ADC. The response
IN
is naturally deglitched by the 100ms typical response time
of the ADC. The fault responses are:
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
Time Interval Specified in MFR_RETRY_DELAY. See
Table 17.

RESPONSES TO OT/UT FAULTS

Internal Overtemperature Fault Response

An internal temperature sensor protects against NVM
damage. Above 85°C, no writes to NVM are recommended.
Above 130°C, the internal overtemperature warn threshold
to
OUT
is exceeded and the part disables the NVM and does not re-
enable until the temperature has dropped to 125°C. When
the die temperature exceed 160°C the internal temperature
fault response is enabled and the PWM is disabled until
the die temperature drops below 150°C. Temperature is
measured by the ADC. Internal temperature faults cannot
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LTM4700
OV FAULTS
IN
Rev. B
37