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OPERATION
Three dedicated pins for ALERT, PGOOD0/PGOOD1 func-
tions are provided. The shutdown operation also allows
all faults to be individually masked and can be operated
in either unlatched (hiccup) or latched modes.
Individual status commands enable fault reporting over
the serial bus to identify the specific fault event. Fault or
warning detection includes the following:
Output Undervoltage/Overvoltage
n
Input Undervoltage/Overvoltage
n
Input and Output Overcurrent
n
Internal Overtemperature
n
Communication, Memory or Logic (CML) Fault
n
EEPROM WITH ECC
The LTM4700 contains internal EEPROM with ECC (Error
Correction Coding) to store user configuration settings and
fault log information. EEPROM endurance retention and
mass write operation time are specified in the Electrical
Characteristics and Absolute Maximum Ratings sections.
Write operations above T
the Electrical Characteristics are not guaranteed and the
EEPROM will be degraded. Read operations performed at
temperatures between –40°C and 125°C will not degrade
the EEPROM. Writing to the EEPROM above 85°C will
result in a degradation of retention characteristics. The
fault logging function, which is useful in debugging system
problems that may occur at high temperatures, only writes
to fault log EEPROM locations. If occasional writes to these
registers occur above 85°C, the slight degradation in the
data retention characteristics of the fault log will not take
away from the usefulness of the function.
It is recommended that the EEPROM not be written
when the die temperature is greater than 85°C. If the die
temperature exceeds 130°C, the LTM4700 will disable all
EEPROM write operations. All EEPROM write operations
will be re-enabled when the die temperature drops below
125°C. (The controller will also disable all the switching
when the die temperature exceeds the internal overtem-
perature fault limit 160°C with a 10°C hysteresis).
= 85°C are possible although
J
For more information
The degradation in EEPROM retention for temperatures
>125°C can be approximated by calculating the dimen-
sionless acceleration factor using the following equation:
⎡
⎛
Ea
1
⎛
⎞
•
⎢
⎝ ⎜
⎠ ⎟
⎝ ⎜
+273
k
T
⎣
AF = e
USE
where:
AF = acceleration factor
Ea = activation energy = 1.4eV
–5
K = 8.617 • 10
eV/°K
T
= 125°C specified junction temperature
USE
T
= actual junction temperature in °C
STRESS
Example: Calculate the effect on retention when operating
at a junction temperature of 135°C for 10 hours.
T
= 130°C
STRESS
T
= 125°C,
USE
([(1.4/8.617 • 10 –5 ) • (1/398 – 1/403)] )
AF = e
The equivalent operating time at 125°C = 16.6 hours.
Thus the overall retention of the EEPROM was degraded
by 16.6 hours as a result of operating at a junction tem-
perature of 130°C for 10 hours. The effect of the overstress
is negligible when compared to the overall EEPROM
retention rating of 87,600 hours at a maximum junction
temperature of 125°C.
The integrity of the entire onboard EEPROM is checked with
a CRC calculation each time its data is to be read, such as
after a power-on reset or execution of a RESTORE_USER_
ALL command. If a CRC error occurs, the CML bit is set in
the STATUS_BYTE and STATUS_WORD commands, the
EEPROM CRC Error bit in the STATUS_MFR_SPECIFIC
command is set, and the ALERT and RUN pins pulled
low (PWM channels off). At that point the device will only
respond at special address 0x7C, which is activated only
after an invalid CRC has been detected. The chip will also
respond at the global addresses 0x5A and 0x5B, but use
of these addresses when attempting to recover from a
CRC issue is not recommended. All power supply rails
associated with either PWM channel of a device reporting
an invalid CRC should remain disabled until the issue is
www.analog.com
LTM4700
⎤
⎞
1
–
⎥
⎠ ⎟
+273
T
⎦
STRESS
= 16.6
23
Rev. B
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