LTM4675 datasheet(22/128 Pages) LINER

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LTC3884/LTC3884-1

3884fe

For more information www.linear.com/LTC3884

OPERATION

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 135°C for 10 hours.

TSTRESS = 130°C

TUSE = 125°C,

AF = e([(1.4/8.617 • 10

–5) • (1/398 – 1/403)] ) = 16.6

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

Thus the overall retention of the EEPROM was degraded by

16.6hoursasaresultofoperatingatajunctiontemperatureof

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.

TheintegrityoftheentireonboardEEPROMischeckedwith

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

resolved. See the application Information section or con-

tact the factory for details on efficient in-system EEPROM

programming, including bulk EEPROM Programming,

which the LTC3884 also supports.

POWER-UP AND INITIALIZATION

The LTC3884 is designed to provide standalone supply

sequencing and controlled turn-on and turn-off operation.

It operates from a single input supply (4.5V to 38V) while

three on-chip linear regulators generate internal 2.5V, 3.3V

and 5.5V. If VIN does not exceed 6V, and the EXTVCC pin

is not driven by an external supply, the INTVCC and VIN

pins must be tied together. The controller configuration is

initialized by an internal threshold based UVLO where VIN

must be approximately 4V and the 5.5V, 3.3V and 2.5V

linear regulators must be within approximately 20% of

the regulated values. In addition to power supply,a PMBus

RESTORE_USER_ALL or MFR_RESET command can

initialize the part too.

TheEXTVCCpinisdrivenbyanexternalregulatortoimprove

efficiency of the circuit and minimize power loss on the

LTC3884 when VIN is high. The EXTVCC pin must exceed

approximately 4.7V, and VIN must exceed approximately

7V before the INTVCC LDO operates from the EXTVCC pin.

To minimize application power, the EXTVCC pin can be

supplied by a switching regulator.

During initialization, the external configuration resistors

are identified and/or contents of the NVM are read into the

controller’scommandsandtheBGn,TGnpinsareheldlow

for LTC3884. The RUNnandFAULTnandPGOODnareheld

low for the LTC3884, or PWM pins are in three-state for the

LTC3884-1. The LTC3884 will use the contents of Table 3

to Table 6 to determine the resistor defined parameters.

See the Resistor Configuration section for more details.

The resistor configuration pins only control some of the

preset values of the controller. The remaining values are

programmed in NVM either at the factory or by the user.

If the configuration resistors are not inserted or if the ignore

RCONFIG bit is asserted (bit 6 of the MFR_CONFIG_ALL

configuration command), the LTC3884 will use only the

contentsofNVMtodeterminetheDC/DCcharacteristics.The

ASEL0/1valuereadatpower-uporresetisalwaysrespected

unless the pin is open. The ASEL0/1 will set the MSB and

the LSB from the detected threshold. See the Applications

Information section for more details.

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