LTM4682 datasheet(28/130 Pages) AD

28 / 130 page

LTM4682

Rev. A

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OPERATION

and FAULT3, outputs are provided. Each FAULTn can be

masked independently.

Six dedicated pins for ALERT_01, ALERT_23, PGOOD0,

PGOOD1, PGOOD2, and PGOOD3 functions are provided.

The shutdown operation also allows all faults to be indi-

vidually 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

Input Undervoltage/Overvoltage

Input and Output Overcurrent

Internal Overtemperature

Communication, Memory or Logic (CML) Fault

EEPROM WITH ECC

The LTM4682 contains internal EEPROM with ECC to

store user configuration settings and fault log information

for Channels 0 and 1, and Channels 2 and 3. The EEPROM

endurance retention and mass write operation time are

specified in the Electrical Characteristics and Absolute

Maximum Ratings sections. Write operations above TJ =

85°C are possible although 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 degrading reten-

tion 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 tem-

perature exceeds 130°C, the LTM4682 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.

The degradation in EEPROM retention for temperatures

>125°C can be approximated by calculating the dimen-

sionless acceleration factor using the following equation:

= e

⎛

⎝⎜

⎞

⎠⎟

•

TUSE+273

–

TSTRESS+273

⎛

⎝⎜

⎞

⎠⎟

⎡

⎣

⎢

⎤

⎦

⎥

where:

AF = acceleration factor

Ea = activation energy = 1.4eV

k = 8.617 • 10–5 eV/K

TUSE = 125°C specified junction temperature

TSTRESS = actual junction temperature in °C

Example: Calculate the effect on retention when operating

at a junction temperature of 130°C for 10 hours.

TSTRESS = 130°C

TUSE = 125°C,

AF = e([(1.4/8.617 • 10

–5) • (1/398 – 1/403)] ) = 1.66

The equivalent operating time at 125°C = 16.6 hours.

Thus the overall retention of the EEPROM was degraded

by 6.6 hours as a result of operating at a junction tempera-

ture of 130°C for 10 hours. The effect of the overstress is

negligible when compared to the overall EEPROM reten-

tion rating of 87,600 hours at a maximum junction tem-

perature 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 a 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 using these addresses when attempting to recover

LTM4682 Datasheet(PDF) 28 Page - Analog Devices

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