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 L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and LTpowerPlay is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. 2977mg 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. 1 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 2977mg 2 Linear Technology Corporation LT 0413 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2013