LTM4680 datasheet(29/132 Pages) AD

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LTM4681

Rev. 0

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OPERATION

Fault reporting and shutdown behavior are fully configu-

rable. Four individual FAULT0, FAULT1, FAULT2, FAULT3,

outputs are provided, both of which can be masked

independently.

Six dedicated pins for ALERT_01, ALERT_23, PGOOD0,

PGOOD1, PGOOD2, PGOOD3 functions 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

Input Undervoltage/Overvoltage

Input and Output Overcurrent

Internal Overtemperature

Communication, Memory or Logic (CML) Fault

EEPROM WITH ECC

The LTM4681 contains internal EEPROM with ECC

(Error Correction Coding) to store user configuration

settings and fault log information for channels 0 and 1,

and channels 2 and 3. 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 a degradation of retention characteristics. The

fault logging function, which is useful in debugging sys-

tem 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 degrada-

tion 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 LTM4681 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 special address 0x7C, which is activated only

after an invalid CRC has been detected. The chip will also

LTM4680 Datasheet(PDF) 29 Page - Analog Devices

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