LTC3882_15 Datasheet, PDF (22/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
OPERATION
The FREQ_CFG pin settings are described in application
Table 9. This pin selects the switching frequency of the
internal oscillator and enables the SYNC output if not left
open, shorted to GND or ignored by EEPROM setting.
The PHAS_CFG pin settings are described in Table 11.
This pin selects the phase relationships between the two
channels and the selected clock source.
Internal EEPROM with CRC
The LTC3882 contains internal EEPROM to store user
configuration settings and fault log information. EEPROM
endurance and retention for user space and fault log
pages are specified in the Absolute Maximum Ratings
and Electrical Characteristics table. The LTC3882 EEPROM
also contains a manufacturing section that has internal
redundancy.
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
resolved.
LTC recommends that the EEPROM not be written when
die temperature is greater than 85°C. If internal die tem-
perature exceeds 130°C, all EEPROM operations except
RESTORE_USER_ALL and MFR_RESET are disabled. Full
EEPROM operation is not re-enabled until die temperature
falls below 125°C. Refer to the Applications Information
section for equations to predict retention degradation due
to elevated operating temperatures.
See the Applications Information section or contact the
factory for details on efficient in-system EEPROM program-
ming, including bulk EEPROM programming, which the
LTC3882 also supports.
Fault Detection
A variety of fault and warning detection, reporting and
handling mechanisms are provided by the LTC3882. Fault
or warning detection capabilities include:
• Input Under/Overvoltage
• Output Under/Overvoltage
• Output Overcurrent (Peak and Average)
• Internal and External Overtemperature and External
Undertemperature
• CML Fault (Communication, Memory, or Logic)
• External Fault Detection via Bidirectional GPIO Pins
Reporting is covered in following sections on status com-
mands (registers) and ALERT pin function. Fault handling
mechanisms include hardwired, low-level PWM safety
responses that always occur, and higher-level program-
mable event management. Both types are covered in the
following sections.
Input Supply Faults
Input undervoltage and overvoltage limits are determined
from multiplexed monitor ADC conversions. Therefore the
input UV/OV response is naturally deglitched by the 100ms
typical conversion cycle of the ADC. There is no hardwired
low-level PWM response for any input supply fault.
Hardwired PWM Response to V_OUT Faults
V_OUT undervoltage (UV) and overvoltage (OV) faults are
detected by supervisor comparators. The OV and UV fault
limits can be set in three ways:
• As a Percentage of V_OUT if Using the Resistor Configu-
ration Pins
• From Stored EEPROM Values
• By PMBus Command
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For more information www.linear.com/LTC3882