LTC2977 - Migration Guide

Migration Guide
LTC2977
INTRODUCTION
The LTC®2977 is a 100% pin-compatible upgrade to the LTC2978/LTC2978A featuring longer TON and TOFF delays,
improved power-up and power good timing specifications, more fault management options, and other enhancements.
This guide describes the differences and explains the configuration file changes needed when migrating a design from
the LTC2978/LTC2978A to the LTC2977.
FEATURE COMPARISON
Sequencing
Time Based
LTC2978/LTC2978A
LTC2977
✓
✓
0.655 Sec
✓
13.1 Sec
100ms
135ms (Typ)
0 or ∞
✓
12μs or 100ms
30ms (Typ)
0 to 6, or ∞
Tracking*
Maximum Programmable TON_DELAY/TOFF_DELAY
Sequence Off Upon Fault
Power Good De-Assertion Time
Power-Up Time
Fault Retry Count Options
Fast Fault Log Mode
✓
EEPROM Bulk Programming (Without Affecting RAM)
✓
Pollable MFR_COMMON Register When Device Is Busy
✓
Command Plus
✓
*Note: Enables use of tracking DC/DC converters. Does not control ramp rates.
PIN CONFIGURATION
The pin configuration of the LTC2977 is 100% compatible with the LTC2978/LTC2978A. No changes to existing hardware
are required to migrate from the LTC2978/LTC2978A to the LTC2977.
ELECTRICAL CHARACTERISTICS
The electrical characteristics of the LTC2977 are the same as the LTC2978/LTC2978A with the following exceptions:
Operating Temperature Range
Storage Temperature Range
GAIN_ADC (Current Sense Mode) Maximum
*Note: Due to the higher operating temperature range of the LTC2977.
LTC2978/LTC2978A
–40°C to 85°C
–40°C to 125°C
±0.2%
LTC2977
–40°C to 105°C
–40°C to 150°C
±0.35%*
CONFIGURATION FILE
The following PMBus commands are new or have changed in the LTC2977. An automatic conversion utility is provided
in LTpowerPlay™ to simplify the transition from an LTC2978/LTC2978A configuration file to a functionally equivalent
LTC2977 configuration file.
Writable Commands
MFR_CONFIG_ALL (0xD1)
LTC2978/LTC2978A
LTC2977
Byte Command
Word Command
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respective owners.
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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Migration Guide
CONFIGURATION FILE
For maximum compatibility with legacy LTC2978/LTC2978A designs, the new MFR_CONFIG_ALL bits [15:8] should
be written to zero. This will disable short-cycle fault detection, fast PWRGD de-assertion, and fast fault logging. Note
that factory programmed LTC2977 devices will have these features enabled by default.
MFR_CONFIG (0xD0), Bits [15:14]
LTC2978/LTC2978A
LTC2977
Reserved
Mfr_config_chan_mode
For maximum compatibility with legacy LTC2978/LTC2978A designs, the new MFR_CONFIG bits [15:14] should be
written to zero.
LTC2978/LTC2978A
MFR_SPARE_0 (0xF7)
MFR_SPARE_2 (0xF9)
N/A
User Scratch Value
User Scratch Value
Retry Count
LTC2977
USER_DATA_04 (0xB4)
USER_DATA_03 (0xB3)
MFR_RETRY_COUNT (0xF7)
The unpaged data in MFR_SPARE_0 has been moved to USER_DATA_04. The 8-paged data in MFR_SPARE_2 has been
moved to USER_DATA_03. The command code 0xF7 is used by the LTC2977 for the new MFR_RETRY_COUNT feature.
LTC2978/LTC2978A
NACK
NACK
NACK
NACK
NACK
NACK
NACK
NACK
NACK
NACK
NACK
USER_DATA_00 (0xB0)
USER_DATA_01 (0xB1)
USER_DATA_02 (0xB2)
MFR_LTC_RESERVED_1 (0xB5)
MFR_LTC_RESERVED_2 (0xBC)
MFR_EE_UNLOCK (0xBD)
MFR_EE_ERASE (0xBE)
MFR_EE_DATA (0xBF)
MFR_COMMAND_PLUS (0xC0)
MFR_DATA_PLUS0 (0xC1)
MFR_DATA_PLUS1 (0xC2)
LTC2977
Reserved
Reserved
Reserved
Reserved
Reserved
New: EEPROM Bulk Access
New: EEPROM Bulk Access
New: EEPROM Bulk Access
New: Command Plus
New: Command Plus
New: Command Plus
These commands will NACK on the LTC2978/LTC2978A. The LTC2977 assigns new functionality to these commands.
Consult the LTC2977 data sheet for more information.
Read-Only Commands
The following read-only commands return different values on the LTC2977 and LTC2978/LTC2978A. No configuration
file changes are required, but interpretation of the values must be changed accordingly.
LTC2978
CAPABILITY (0x19)
MFR_SPECIAL_ID (0xE7)
MFR_COMMON (0xEF)
LTC2978A
LTC2977
0xE0
0xE0
0xB0
0x0122
0x0124
0x0130
Bits [7:2] may return different values
LTC2978/LTC2978A
LTC2977
MFR_STATUS_2 (0xB7)
NACK
New
MFR_TELEMETRY (0xCF)
NACK
New
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