LTC2978A 8-Channel PMBus Power System Manager Featuring Accurate Output Voltage Measurement DESCRIPTION FEATURES n n n n n n n n n n n n n n n n Sequence, Trim, Margin and Supervise Eight Power Supplies Manage Faults, Monitor Telemetry and Create Fault Logs PMBus Compliant Command Set Supported by LTpowerPlay™ GUI Margin or Trim Supplies to 0.
LTC2978A TABLE OF CONTENTS Features...................................................... 1 Applications................................................. 1 Typical Application......................................... 1 Description.................................................. 1 Absolute Maximum Ratings............................... 4 Order Information........................................... 4 Pin Configuration........................................... 4 Electrical Characteristics...................
LTC2978A TABLE OF CONTENTS MFR_VINEN_OV_FAULT_RESPONSE..................48 MFR_VINEN_UV_FAULT_RESPONSE.................. 49 MFR_RETRY_DELAY........................................... 49 MFR_RESTART_DELAY.......................................50 MFR_VOUT_PEAK...............................................50 MFR_VIN_PEAK..................................................50 MFR_TEMPERATURE_PEAK...............................50 MFR_DAC............................................................
LTC2978A Supply Voltages: VPWR to GND.......................................... –0.3V to 15V VDD33 to GND........................................ –0.3V to 3.6V VDD25 to GND...................................... –0.3V to 2.75V Digital Input/Output Voltages: ALERTB, SDA, SCL, CONTROL0, CONTROL1............................................. –0.3V to 5.5V PWRGD, SHARE_CLK, WDI/RESETB, WP.....................–0.3V to VDD33 + 0.3V FAULTB00, FAULTB01, FAULTB10, FAULTB11.................................–0.
LTC2978A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VPWR = VIN_SNS = 12V, VDD33, VDD25, REFP and REFM pins floating, unless otherwise indicated. CVDD33 = 100nF, CVDD25 = 100nF and CREF = 100nF. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 15 V 10 13 mA 10 13 mA 2.55 2.8 V Power-Supply Characteristics VPWR VPWR Supply Input Operating Range IPWR VPWR Supply Current 4.
LTC2978A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VPWR = VIN_SNS = 12V; VDD33, VDD25, REFP and REFM pins floating, unless otherwise indicated. CVDD33 = 100nF, CVDD25 = 100nF and CREF = 100nF.
LTC2978A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VPWR = VIN_SNS = 12V; VDD33, VDD25, REFP and REFM pins floating, unless otherwise indicated. CVDD33 = 100nF, CVDD25 = 100nF and CREF = 100nF. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS DAC Soft-Connect Comparator Characteristics VOS_CMP Offset Voltage VDACPn = 0.2V l ±1 ±18 mV VDACPn = 1.3V l ±2 ±26 mV VDACPn = 2.
LTC2978A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VPWR = VIN_SNS = 12V; VDD33, VDD25, REFP and REFM pins floating, unless otherwise indicated. CVDD33 = 100nF, CVDD25 = 100nF and CREF = 100nF.
LTC2978A ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating for extended periods may affect device reliability and lifetime. Note 2: All currents into device pins are positive. All currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified. If power is supplied to the chip via the VDD33 pin only, connect VPWR and VDD33 pins together.
LTC2978A TYPICAL PERFORMANCE CHARACTERISTICS ADC Total Unadjusted Error vs Temperature Temperature Sensor Error vs Temperature Reference Voltage vs Temperature 1.6 0.035 1.2350 1.4 0.030 REFERENCE OUTPUT VOLTAGE (V) 1.2355 1.2345 1.2 1.2340 ERROR (%) 1.2330 0.025 1.0 ERROR (°C) 1.2335 0.8 0.6 1.2325 THREE TYPICAL PARTS 1.
LTC2978A TYPICAL PERFORMANCE CHARACTERISTICS 1200 NUMBER OF READINGS REJECTION (dB) –60 –80 0 3125 6250 9375 FREQUENCY (Hz) –0.10 800 600 400 –0.25 –10 0 10 READ_VOUT (µV) –0.40 –50 –35 –20 –5 10 25 40 55 70 85 100 TEMPERATURE (°C) 20 2978a G11 Input Sampling Current vs Differential Input Voltage 2978a G12 DAC Full-Scale Output Voltage vs Temperature ADC High Resolution Mode Differential Input Current 9 90 2.698 8 80 2.
LTC2978A TYPICAL PERFORMANCE CHARACTERISTICS DAC Load Regulation (Sourcing) 85°C 2.696 25°C 2.692 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 2.694 2.690 2.688 2.686 2.684 2.682 2.678 9.00 0.1036 8.95 85°C 0.1034 25°C 0.1032 0.1030 –40°C 0.1028 –40°C 2.680 0.1038 0 –0.25 –0.5 –0.75 –1 –1.25 –1.50 1.75 CURRENT (mA) –2 SHORT-CIRCUIT CURRENT (mA) 2.698 DAC Short-Circuit Current vs Temperature DAC Load Regulation (Sinking) 0.1026 0 0.25 0.5 0.75 1 1.25 1.5 1.
LTC2978A TYPICAL PERFORMANCE CHARACTERISTICS VDD33 Regulator Output Voltage vs Temperature –86 400 300 3.265 200 3.260 3.255 3.250 3.245 85°C 25°C 100 –40°C 0 –100 –200 –300 3.240 –400 3.235 –50 –35 –20 –5 10 25 40 55 70 85 100 TEMPERATURE (°C) –500 4.5 6 7.5 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 9 10.5 VPWR (V) 12 13.5 15 9.9 10.12 10.10 10.08 10.06 3.1 3.2 3.3 3.4 3.5 3.
LTC2978A TYPICAL PERFORMANCE CHARACTERISTICS VOUT_EN[3:0] and VIN_EN VOL vs Current DAC Output Impedance vs Frequency 100 VOUT_EN[7:4] VOL vs Current 1.4 0.6 1.2 0.5 1.0 1 0.4 85°C 0.8 25°C 0.6 0.01 0.01 10 1 FREQUENCY (kHz) 100 –40°C 0.1 0 1000 0 2 4 8 6 ISINK (mA) 0 4 8 12 16 ISINK (mA) 20 24 2978a G33 2978a G32 PWRGD and FAULTBzn VOL vs Current ALERTB VOL vs Current 1.2 1.4 1.0 1.2 1.0 VOLTS (V) 0.8 VOLTS (V) 0 12 10 2978a G31 0.6 0.4 85°C 0.8 25°C 0.
LTC2978A PIN FUNCTIONS PIN NAME VSENSEM6 VSENSEP7 VSENSEM7 VOUT_EN0 VOUT_EN1 VOUT_EN2 VOUT_EN3 VOUT_EN4 VOUT_EN5 VOUT_EN6 VOUT_EN7 VIN_EN DNC VIN_SNS PIN NUMBER PIN TYPE 1* In 2* In 3* In 4 Out 5 Out 6 Out 7 Out 8 Out 9 Out 10 Out 11 Out 12 0ut 13 Do Not Connect 14 In VPWR 15 In VDD33 16 In/Out VDD33 VDD25 WP PWRGD 17 18 19 20 In In/Out In Out SHARE_CLK WDI/RESETB 21 22 In/Out In FAULTB00 23 In/Out FAULTB01 24 In/Out FAULTB10 25 In/Out FAULTB11 26 In/Out SDA SCL ALERTB CONTROL0 CON
LTC2978A PIN FUNCTIONS PIN NAME PIN NUMBER PIN TYPE DESCRIPTION 41* Out DAC1 Return. Connect to Channel 1 DC/DC Converter’s GND Sense or Return to GND VDACM1 42* In DC/DC Converter Differential (+) Output Voltage or Current-1 Sensing Pins VSENSEP1 43* In DC/DC Converter Differential (–) Output Voltage or Current-1 Sensing Pins VSENSEM1 44 Out DAC2 Output VDACP2 45* Out DAC2 Return.
LTC2978A BLOCK DIAGRAM 3.3V REGULATOR VOUT VIN VPWR 15 VDD VDD33 16 2.
LTC2978A OPERATION OPERATION OVERVIEW n The LTC2978A is a PMBus programmable power system controller, monitor, sequencer and voltage supervisor that can perform the following operations: n Accept PMBus compatible programming commands. n n n n n n n n n n n n Provide DC/DC converter input voltage and output voltage/current read back through the PMBus interface.
LTC2978A OPERATION Nondestructive operation above TJ = 85°C is possible although the Electrical Characteristics are not guaranteed and the EEPROM will be degraded. Operating the EEPROM above 85°C may result in a degradation of retention characteristics. The fault logging function, which is useful in debugging system problems that may occur at high temperatures, only writes to fault log EEPROM locations.
LTC2978A OPERATION chip will respond by beginning a soft-start sequence. In this case the slowest VIN_ON detection will take over and synchronize other chips to its soft-start sequence. PMBus SERIAL DIGITAL INTERFACE The LTC2978A communicates with a host (master) using the standard PMBus serial bus interface. The PMBus Timing Diagram shows the timing relationship of the signals on the bus. The two bus lines, SDA and SCL, must be high when the bus is not in use.
LTC2978A OPERATION 1 7 S 1 1 SLAVE ADDRESS Wr A COMMAND CODE A x x 1 1 8 P S Sr Rd Wr x START CONDITION REPEATED START CONDITION READ (BIT VALUE OF 1) WRITE (BIT VALUE OF 0) SHOWN UNDER A FIELD INDICATES THAT THE FIELD IS REQUIRED TO HAVE THE VALUE OF x A ACKNOWLEDGE (THIS BIT POSITION MAY BE 0 FOR AN ACK OR 1 FOR A NACK) P STOP CONDITION PEC PACKET ERROR CODE MASTER TO SLAVE SLAVE TO MASTER ... CONTINUATION OF PROTOCOL 2978a F01a Figure 1a.
LTC2978A OPERATION 1 S 7 1 1 8 1 1 SLAVE ADDRESS Wr A COMMAND CODE A 7 1 1 Sr SLAVE ADDRESS Rd A 8 1 DATA BYTE LOW A 1 1 DATA BYTE HIGH A 8 P 1 2978a F07 Figure 7. Read Word Protocol 1 S 7 1 1 8 1 1 7 1 1 SLAVE ADDRESS Wr A COMMAND CODE A Sr SLAVE ADDRESS Rd A 8 1 DATA BYTE LOW A 8 1 DATA BYTE HIGH A 8 1 1 PEC A P 1 2978a F08 Figure 8.
LTC2978A OPERATION Device Address The I2C/SMBus address of the LTC2978A equals the base address + N where N is a number from 0 to 8. N can be configured by setting the ASEL0 and ASEL1 pins to VDD33, GND or FLOAT. See Table 1. Using one base address and the nine values of N, nine LTC2978As can be connected together to control 72 outputs. The base address is stored in the MFR_I2C_BASE_ADDRESS register.
LTC2978A OPERATION Processing Commands The LTC2978A uses a dedicated processing block to ensure quick response to all of its commands. There are a few exceptions where the part will NACK a subsequent command because it is still processing the previous command. These are summarized in the following tables. EEPROM Related Commands COMMAND STORE_USER_ALL TYPICAL DELAY* tMASS_WRITE COMMENT See Electrical Characteristics table.
LTC2978A PMBus COMMAND SUMMARY Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE PAGE 0x00 Channel or page currently selected for any R/W Byte command that supports paging. N Reg 0x00 30 OPERATION 0x01 Operating mode control. On/Off, Margin High and Margin Low. R/W Byte Y Reg Y 0x00 31 ON_OFF_CONFIG 0x02 CONTROL pin & PMBus bus on/off command setting.
LTC2978A PMBus COMMAND SUMMARY Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE OT_FAULT_RESPONSE 0x50 Action to be taken by the device when an overtemperature fault is detected. R/W Byte N Reg Y 0xB8 37 OT_WARN_LIMIT 0x51 Overtemperature warning limit. R/W Word N L11 °C Y 75.0 0xEA58 35 UT_WARN_LIMIT 0x52 Undertemperature warning limit.
LTC2978A PMBus COMMAND SUMMARY Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE STATUS_INPUT 0x7C Input voltage fault and warning status measured at VIN_SNS pin. R Byte N Reg NA 40 STATUS_TEMPERATURE 0x7D Temperature fault and warning status for READ_TEMPERATURE_1. R Byte N Reg NA 40 STATUS_CML 0x7E Communication and memory fault and warning status.
LTC2978A PMBus COMMAND SUMMARY Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE MFR_DAC 0xE0 Manufacturer register that contains the code of the 10-bit DAC. R/W Word Y Reg 0x0000 51 MFR_POWERGOOD_ ASSERTION_DELAY 0xE1 Power good output assertion delay. R/W Word N L11 ms Y 100.0 0xEB20 51 MFR_WATCHDOG_T_FIRST 0xE2 First watchdog timer interval.
LTC2978A PMBus COMMAND SUMMARY Data Formats L11 Linear_5s_11s L16 Linear_16u Reg Register CF Custom Format PMBus data field b[15:0] Value = Y • 2N where N = b[15:11] is a 5-bit two’s complement integer and Y = b[10:0] is an 11-bit two’s complement integer Example: READ_VIN = 10V For b[15:0] = 0xD280 = 1101_0010_1000_0000b Value = 640 • 2–6 = 10 See PMBus Spec Part II: Paragraph 7.
LTC2978A PMBus COMMAND DESCRIPTION OPERATION, MODE AND EEPROM COMMANDS PAGE The LTC2978A has eight pages that correspond to the eight DC/DC converter channels that can be managed. Each DC/DC converter channel can be uniquely programmed by first setting the appropriate page. The PAGE command provides the ability to configure, control and monitor multiple outputs on one unit. Setting PAGE = 0xFF allows a simultaneous write to all pages for PMBus commands that support global page programming.
LTC2978A PMBus COMMAND DESCRIPTION OPERATION The OPERATION command is used to turn the unit on and off in conjunction with the CONTROLn pin and ON_OFF_ CONFIG. This command register responds to the global page command (PAGE=0xFF). The contents and functions of the data byte are shown in the following tables. A minimum tOFF_MIN wait time must be observed between OPERATION commands used to turn the unit off and then back on.
LTC2978A PMBus COMMAND DESCRIPTION ON_OFF_CONFIG The ON_OFF_CONFIG command configures the combination of CONTROLn pin input and PMBus bus commands needed to turn the LTC2978A on/off, including the power-on behavior, as shown in the following table. This command register responds to the global page command (PAGE=0xFF). After the part has initialized, an additional comparator monitors VIN_SNS. The VIN_ON threshold must be exceeded before the output power sequencing can begin.
LTC2978A PMBus COMMAND DESCRIPTION WRITE_PROTECT The WRITE_PROTECT command provides protection against accidental programming of the LTC2978A command registers. All supported commands may have their parameters read, regardless of the WRITE_PROTECT setting. There are two levels of write protection: • Level 1: Nothing can be changed except the level of write protection itself. Values can be read from all pages. This setting can be stored to EEPROM.
LTC2978A PMBus COMMAND DESCRIPTION VOUT_MODE This command is read only and specifies the mode and exponent for all commands with a L16 data format. See Data Formats table on page 29. VOUT_MODE Data Contents BIT(S) SYMBOL OPERATION b[7:5] Vout_mode_type Reports linear mode. Hard wired to 000b. b[4:0] Vout_mode_parameter Linear mode exponent. 5-bit two’s complement integer. Hardwired to 0x13 (–13 decimal).
LTC2978A PMBus COMMAND DESCRIPTION TEMPERATURE RELATED COMMANDS OT_FAULT_LIMIT, OT_WARN_LIMIT, UT_WARN_LIMIT and UT_FAULT_LIMIT These commands provide supervising limits for temperature. Data Contents BIT(S) SYMBOL OPERATION b[15:0] Ot_fault_limit[15:0], The data uses the L11 format. Ot_warn_limit[15:0], Units: °C.
LTC2978A PMBus COMMAND DESCRIPTION FAULT RESPONSE FOR VOLTAGES MEASURED BY THE HIGH SPEED SUPERVISOR VOUT_OV_FAULT_RESPONSE and VOUT_UV_FAULT_RESPONSE The fault response documented here is for voltages that are measured by the high speed supervisor. These voltages are measured over a short period of time and may require a deglitch period.
LTC2978A PMBus COMMAND DESCRIPTION FAULT RESPONSE FOR VALUES MEASURED BY THE ADC OT_FAULT_RESPONSE, UT_FAULT_RESPONSE, VIN_OV_FAULT_RESPONSE and VIN_UV_FAULT_RESPONSE The fault response documented here is for values that are measured by the ADC. These values are measured over a longer period of time and are not deglitched.
LTC2978A PMBus COMMAND DESCRIPTION TON_MAX_FAULT_RESPONSE Data Contents BIT(S) SYMBOL OPERATION b[7:6] Ton_max_fault_response_action Response action: 00b: The unit continues operation without interruption. 01b: The unit continues operating for the delay time specified which for this type of fault corresponds to an immediate shutdown. After shutting off, the device responds according to the retry settings in bits [5:3]. 1Xb: The device shuts down and responds according to the retry setting in bits [5:3].
LTC2978A PMBus COMMAND DESCRIPTION STATUS_WORD The STATUS_WORD command returns two bytes of information with a summary of the unit’s fault condition. Based on the information in these bytes, the host can get more information by reading the appropriate detailed status register. The low byte of the STATUS_WORD is the same register as the STATUS_BYTE command. STATUS_WORD Data Contents BIT(S) SYMBOL OPERATION b[15] Status_word_vout An output voltage fault or warning has occurred. See STATUS_VOUT.
LTC2978A PMBus COMMAND DESCRIPTION STATUS_INPUT The STATUS_INPUT command returns the summary of the VIN faults or warnings which have occurred, as shown in the following table: STATUS_INPUT Data Contents BIT(S) SYMBOL OPERATION b[7] Status_input_ov_fault VIN Overvoltage fault b[6] Status_input_ov_warn VIN Overvoltage warning b[5] Status_input_uv_warn VIN Undervoltage warning b[4] Status_input_uv_fault VIN Undervoltage fault b[3] Status_input_off Unit is off for insufficient input voltage.
LTC2978A PMBus COMMAND DESCRIPTION STATUS_CML The STATUS_CML command returns the summary of the communication, memory and logic faults or warnings which have occurred, as shown in the following table: STATUS_CML Data Contents BIT(S) SYMBOL OPERATION b[7] Status_cml_cmd_fault Illegal or unsupported command fault has occurred. b[6] Status_cml_data_fault Illegal or unsupported data received. b[5] Status_cml_pec_fault A PEC fault has occurred. Note: PEC checking is always active in the LTC2978A.
LTC2978A PMBus COMMAND DESCRIPTION ADC MONITORING COMMANDS READ_VIN This command returns the most recent ADC measured value of the voltage measured at the VIN_SNS pin. READ_VIN Data Contents BIT(S) SYMBOL OPERATION b[15:0] Read_vin[15:0] The data uses the L11 format. Units: V READ_VOUT This command returns the most recent ADC measured value of the channel’s output voltage. When odd channels are configured to measure current, the data contents use the L11 format with units in mV.
LTC2978A PMBus COMMAND DESCRIPTION MANUFACTURER SPECIFIC COMMANDS MFR_CONFIG_LTC2978 This command is used to configure various manufacturer specific operating parameters for each channel. MFR_CONFIG_LTC2978 Data Contents BIT(S) SYMBOL b[15:12] Reserved b[11] Mfr_config_fast_servo_off b[10] b[9] b[8] b[7] b[6] b[5:4] OPERATION Don’t care. Always returns 0. Disables fast servo when margining or trimming output voltages: 0: fast-servo enabled. 1: fast-servo disabled.
LTC2978A PMBus COMMAND DESCRIPTION MFR_CONFIG_LTC2978 Data Contents BIT(S) b[0] SYMBOL Mfr_config_dac_pol OPERATION DAC output polarity. 0: Encodes negative (inverting) DC/DC converter trim input. 1: Encodes positive (noninverting) DC/DC converter trim input. MFR_CONFIG_ALL_LTC2978 This command is used to configure parameters that are common to all channels on the IC. They may be set or reviewed from any PAGE setting.
LTC2978A PMBus COMMAND DESCRIPTION MFR_FAULTBz0_PROPAGATE, MFR_FAULTBz1_PROPAGATE These manufacturer specific commands enable channels that have faulted off to propagate that state to the appropriate fault pin. Faulted off states for pages 0 through 3 can only be propagated to pins FAULTB00 and FAULTB01; this is referred to as zone 0. Faulted off states for pages 4 through 7 can only be propagated to pins FAULTB10 and FAULTB11; this is referred to as zone 1.
LTC2978A PMBus COMMAND DESCRIPTION MFR_PWRGD_EN This command register controls the mapping of the watchdog and channel power good status to the PWRGD pin. Note that odd numbered channels whose ADC is in high res mode do not contribute to power good. MFR_PWRGD_EN Data Contents BIT(S) SYMBOL OPERATION b[15:9] Reserved Read only, always returns 0s.
LTC2978A PMBus COMMAND DESCRIPTION MFR_FAULTB00_RESPONSE, MFR_FAULTB01_RESPONSE, MFR_FAULTB10_RESPONSE and MFR_ FAULTB11_RESPONSE These manufacturer specific commands share the same format and specify the response to assertions of the FAULTB pins. For fault zone 0, MFR_FAULTB00_RESPONSE determines whether channels 0 to 3 shut off when the FAULTB00 pin is asserted, and MFR_FAULTB01_RESPONSE determines whether channels 0 to 3 shut off when the FAULTB01 pin is asserted.
LTC2978A PMBus COMMAND DESCRIPTION MFR_VINEN_OV_FAULT_RESPONSE This command register determines whether VOUT overvoltage faults from a given channel cause the VIN_EN pin to be pulled low. MFR_VINEN_OV_FAULT_RESPONSE Data Contents BIT(S) SYMBOL b[7] Mfr_vinen_ov_fault_response_chan7 OPERATION Response to channel 7 VOUT_OV_FAULT. 1 = Disable (pull low) VIN_EN via fast pull-down. 0 = Do not disable VIN_EN. b[6] Mfr_vinen_ov_fault_response_chan6 Response to channel 6 VOUT_OV_FAULT.
LTC2978A PMBus COMMAND DESCRIPTION MFR_VINEN_UV_FAULT_RESPONSE This command register determines whether VOUT undervoltage faults from a given channel cause the VIN_EN pin to be pulled low. MFR_VINEN_UV_FAULT_RESPONSE Data Contents BIT(S) SYMBOL b[7] OPERATION Mfr_vinen_uv_fault_response_chan7 Response to channel 7 VOUT_UV_FAULT. 1 = Disable (pull low) VIN_EN via fast pull-down. 0 = Do not disable VIN_EN. b[6] Mfr_vinen_uv_fault_response_chan6 Response to channel 6 VOUT_UV_FAULT.
LTC2978A PMBus COMMAND DESCRIPTION MFR_RESTART_DELAY This command sets the minimum off time of a CONTROL initiated restart. If the CONTROL pin is toggled off for at least 10µs then on, all dependent channels are disabled, held off for a time = Mfr_restart_delay, then sequenced back on. CONTROLn pin transitions whose OFF time exceeds Mfr_restart_delay are not affected by this command. A value of all zeros disables this feature.
LTC2978A PMBus COMMAND DESCRIPTION MFR_DAC This command register allows the user to directly program the 10-bit DAC. Manual DAC writes require the channel to be in the ON state,TON_RISE to have expired and MFR_CONFIG_LTC2978 b[5:4] = 10b or 11b. Writing MFR_ CONFIG_LTC2978 b[5:4] = 10b commands the DAC to hard-connect with the value in Mfr_dac_direct_val. Writing b[5:4] = 11b commands the DAC to soft-connect.
LTC2978A PMBus COMMAND DESCRIPTION MFR_WATCHDOG_T_FIRST and MFR_WATCHDOG_T Data Contents BIT(S) SYMBOL OPERATION b[15:0] Mfr_watchdog_t_first The data uses the L11 format. Mfr_watchdog_t These timers operate on an internal clock. The Mfr_watchdog_t timer will align to SHARE_CLK if it is running. Delays are rounded to the nearest 10µs for _t and 1ms for _t_first. Writing a zero value for Y to the Mfr_watchdog_t or Mfr_watchdog_t_first registers will disable the watchdog timer. Units: ms. Max timeout is 0.
LTC2978A PMBus COMMAND DESCRIPTION MFR_PADS The MFR_PADS command provides read only access to slow frequency digital pads (pins). The input values presented in bits[9:0] are before any deglitching logic.
LTC2978A PMBus COMMAND DESCRIPTION MFR_SPECIAL_LOT These paged registers contain information that identifies the user configuration that was programmed at the factory. MFR_SPECIAL_LOT Data Contents BIT(S) SYMBOL OPERATION b[7:0] Mfr_special_lot Contains the LTC default special lot number. Contact the factory to request a custom factory programmed user configuration and special lot number.
LTC2978A PMBus COMMAND DESCRIPTION All MFR_SPARE registers may be stored and recalled from EEPROM using the STORE_USER_ALL and RESTORE_ USER_ALL commands. MFR_VOUT_MIN This command returns the minimum ADC measured value of the channel’s output voltage. This register is reset to 0xFFFF (7.999) when the LTC2978A emerges from power-on reset or when a CLEAR_FAULTS command is executed. When odd channels are configured to measure current, this command is not supported.
LTC2978A PMBus COMMAND DESCRIPTION RAM 255 BYTES EEPROM 255 BYTES 8 ADC READINGS CONTINUOUSLY FILL BUFFER TIME OF FAULT TRANSFER TO EEPROM AND LOCK .. . .. . AFTER FAULT READ FROM EEPROM AND LOCK BUFFER 2978a F13 Figure 13. Fault Log Conceptual Diagram MFR_FAULT_LOG_STORE This command allows the user to transfer data from the RAM buffer to EEPROM. MFR_FAULT_LOG_RESTORE This command allows the user to transfer a copy of the fault-log data from the EEPROM to the RAM buffer.
LTC2978A PMBus COMMAND DESCRIPTION MFR_FAULT_LOG Read only. This 2040-bit (255 byte) data block contains a copy of the RAM buffer fault log. The RAM buffer is continuously updated after each ADC conversion as long as Mfr_fault_log_status_ram is clear. With Mfr_config_all_fault_log_enable = 1 and Mfr_fault_ log_status_eeprom = 0, the RAM buffer is transferred to EEPROM whenever an LTC2978A fault causes a channel to latch off or a MFR_FAULT_LOG_STORE command is received.
LTC2978A PMBus COMMAND DESCRIPTION Table 2. Data Block Contents DATA Mfr_vout_peak7[7:0] Mfr_vout_peak7[15:8] Mfr_vout_min7[7:0] Mfr_vout_min7[15:8] BYTE* 43 44 45 46 DESCRIPTION 47 bytes for preamble Fault_log [Position_last] Fault_log . . . Fault_log Reserved 47 48 237 Last Valid Byte 238-254 Number of loops (238-47)/40 = 4.8 *Note: PMBus data byte numbers start at 1 rather than 0. Position_last is the first byte returned after BYTE COUNT = OxFF. See block read protocol.
LTC2978A PMBus COMMAND DESCRIPTION BYTE BYTE NUMBER NUMBER DECIMAL HEX DATA DESCRIPTION BYTE BYTE NUMBER NUMBER DECIMAL HEX DATA 5 05 SharedTime[39:32] 44 2C Mfr_vout_peak7[15:8] Mfr_vout_min7[7:0] 6 06 SharedTime[40] 45 2D 7 07 Mfr_vout_peak0[7:0] 46 2E 8 08 Mfr_vout_peak0[15:8] Mfr_vout_min7[15:8] DESCRIPTION End of Preamble CYCLICAL DATA LOOPS 9 09 Mfr_vout_min0[7:0] 10 0A Mfr_vout_min0[15:8] 11 0B Mfr_vout_peak1[7:0] 12 0C Mfr_vout_peak1[15:8] 47 2F 9 Read_vin[
LTC2978A PMBus COMMAND DESCRIPTION LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL 75 76 4B 4C 21 20 DATA LOOP 1 40 BYTES PER LOOP LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL DATA LOOP 2 Read_ temperature_1[15:8] 109 6D 27 Status_mfr4 Read_ temperature_1[7:0] 110 6E 26 Status_vout4 111 6F 25 Read_vout4[15:8] 112 70 24 Read_vout4[7:0] 113 71 23 Reserved 114 72 22 Status_temp 115 73 21 Read_ temperature_1[15:8] 116 74 20 Read_ temperature_1
LTC2978A PMBus COMMAND DESCRIPTION LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL DATA LOOP 3 40 BYTES PER LOOP LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL DATA LOOP 4 142 8E 34 Status_vout6 177 B1 39 Status_mfr7 143 8F 33 Read_vout6[15:8] 178 B2 38 Status_vout7 144 90 32 Read_vout6[7:0] 179 B3 37 Read_vout7[15:8] 145 91 31 Status_mfr5 180 B4 36 Read_vout7[7:0] 146 92 30 Status_vout5 181 B5 35 Status_mfr6 147 93 29 Read_vout5[15:
LTC2978A PMBus COMMAND DESCRIPTION LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL RESERVED BYTES DATA LOOP 4 212 D4 4 Read_vout1[7:0] 213 D5 3 Status_mfr0 214 D6 2 Status_vout0 215 D7 1 Read_vout0[15:8] 216 D8 0 Read_vout0[7:0] LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL DATA LOOP 5 40 BYTES PER LOOP 40 BYTES PER LOOP 238 EE 0x00 239 EF 0x00 240 F0 0x00 241 F1 0x00 242 F2 0x00 243 F3 0x00 244 F4 0x00 245 F5 0x00 246 F6 0x00
LTC2978A APPLICATIONS INFORMATION OVERVIEW The LTC2978A is a power management IC that is capable of sequencing, margining, trimming, supervising output voltage for OV/UV conditions, providing fault management, and voltage read back for eight DC/DC converters. Input voltage and LTC2978A junction temperature read back are also available. Odd numbered channels can be configured to read back sense resistor voltages to provide current measurements for those channels.
LTC2978A APPLICATIONS INFORMATION Some examples of typical ON/OFF configurations are: On State Operation 1. A DC/DC converter may be configured to turn on anytime VIN exceeds VIN_ON. Once a channel has reached the ON state, the OPERATION command can be used to command the DC/DC converter’s output to margin high, margin low, or return to a nominal output voltage indicated by VOUT_COMMAND.
LTC2978A APPLICATIONS INFORMATION As part of continuous/noncontinuous trim mode, fast servo mode can be used to speed up large output transitions, such as margin commands, or ON events. To use, set Mfr_config_fast_servo_off=0. When enabled, fast servo is started by a change to the target voltage or a new softconnect. The DAC is ramped one lsb every tS_VDACP period until it is near the new target voltage, at which point slow servo mode is entered to avoid overshoot. Noncontinuous servo on warn mode.
LTC2978A APPLICATIONS INFORMATION continue to be held off, the appropriate bit is set in the STATUS_MFR_SPECIFIC register, and the ALERTB pin will be asserted low. When the output voltage has decayed below its OFF threshold, the channel can enter the ON state. Automatic Restart Via MFR_RESTART_DELAY Command and CONTROLn pin An automatic restart sequence can be initiated by driving the CONTROL pin to the off state for >10μs then releasing it.
LTC2978A APPLICATIONS INFORMATION A charge-pumped 5µA pull-up to 12V is also available on the VIN_EN output. Refer to the MFR_CONFIG_ALL_LTC2978 register description in the PMBus COMMAND DESCRIPTION section for more information. Figure 18 shows an application circuit where the VIN_EN output is used to trigger a SCR crowbar on the intermediate bus in order to protect the DC/DC converter’s load from a catastrophic fault such as a stuck top gate.
LTC2978A APPLICATIONS INFORMATION Mfr_faultb00_response, page = 0 Mfr_faultb01_response, page = 0 CHANNEL 0 EVENT PROCESSOR PAGE = 0 Mfr_faultb00_response, page = 1 Mfr_faultb01_response, page = 1 CHANNEL 1 EVENT PROCESSOR PAGE = 1 Mfr_faultb00_response, page = 2 Mfr_faultb01_response, page = 2 CHANNEL 2 EVENT PROCESSOR PAGE = 2 Mfr_faultb00_response, page = 3 Mfr_faultb01_response, page = 3 CHANNEL 3 EVENT PROCESSOR PAGE = 3 Mfr_faultbz0_propagate_ch0 FAULTED_OFF Mfr_faultbz1_propagate_ch0 FAULTB0
LTC2978A APPLICATIONS INFORMATION • A FAULTBzn pin can also be asserted low by an external driver in order to initiate an immediate off-sequence after a 10µs deglitch delay. INTERCONNECT BETWEEN MULTIPLE LTC2978A’S Figure 20 shows how to interconnect the pins in a typical multi-LTC2978A array. • All VIN_SNS lines should be tied together in a star type connection at the point where VIN is to be sensed.
LTC2978A APPLICATIONS INFORMATION • PWRGD reflects the status of the outputs that are mapped to it by the MFR_PWRGD_EN command. Figure 20 shows all the PWRGD pins connected together, but any combination may be used. Note that the latency of the PWRGD pin response may be in the range of 30ms to 185ms depending on ADC MUX settings. See Electrical Characteristics Table Note 4. A fast deassertion of PWRGD may be implemented by wire ANDing the VIN_EN pin with the PWRGD pin.
LTC2978A APPLICATIONS INFORMATION Four-Step Resistor Selection Procedure for DC/DC Converters with External Feedback Resistors The following four-step procedure should be used to calculate the resistor values required for the application circuit shown in Figure 23. 1. Assume values for feedback resistor R20 and the nominal DC/DC converter output voltage VDC(NOM), and solve for R10. VDC(NOM) is the output voltage of the DC/DC converter when the LTC2978A’s VDACP0 pin is in a high impedance state.
LTC2978A APPLICATIONS INFORMATION Trimming and Margining DC/DC Converters with a TRIM Pin Figure 24 illustrates a typical application circuit for trimming/margining the output voltage of a DC/DC converter with a TRIM Pin. The LTC2978A’s VDACP0 pin connects to the TRIM pin through resistor R30, and the VDACM0 pin is connected to the converter’s point-of-load ground. For this configuration, set the DAC polarity bit Mfr_config_ dac_pol in MFR_CONFIG_LTC2978 to 1.
LTC2978A APPLICATIONS INFORMATION LTC2978 bit b[9] = 1 in order to enable high res mode. The VOUT_EN pin will assert low in this mode and cannot be used to control a DC/DC converter. The VDACP output pin is also unavailable. Measuring Current with a Sense Resistor A circuit for measuring current with a sense resistor is shown in Figure 25. The balanced filter rejects both common mode and differential mode noise from the output of the DC/DC converter.
LTC2978A APPLICATIONS INFORMATION Single Phase Design Example Measuring Multiphase Currents As a design example for a DCR current sense application, assume L = 2.2μH, DCR = 10mΩ, and FSW = 500kHz. For current sense applications with more than one phase, RC averaging may be employed. Figure 27 shows an example of this approach for a 3-phase system with DCR current sensing.
LTC2978A APPLICATIONS INFORMATION Anti-aliasing Filter Considerations Noisy environments require an anti-aliasing filter on the input to the LTC2978A’s ADC. The R-C circuit shown in Figure 28 is adequate for most situations. Keep R40 = R50 ≤ 200Ω to minimize ADC gain errors, and select a value for capacitors C10 and C20 that does not add too much additional response time to the OV/UV supervisor, e.g. τ ≅ 10µs (R = 100Ω, C = 0.10µF). has a typical output voltage of 1.23V.
LTC2978A APPLICATIONS INFORMATION Connecting the DC1613 USB to I2C/SMBus/PMBus Controller to the LTC2978A in System The DC1613 USB to I2C/SMBus/PMBus Controller can be interfaced to LTC2978As on the user’s board for programming, telemetry and system debug. The controller, when used in conjunction with LTpowerPlay software, provides a powerful way to debug an entire power system. Failures are quickly diagnosed using telemetry, fault status registers and the fault log.
LTC2978A APPLICATIONS INFORMATION node because this will interfere with bus communication in the absence of system power. Figure 31 shows the recommended schematic to use when the LTC2978A is powered by the system 3.3V through its VDD33 and VPWR pins. The LTC4412 ideal ORing circuit allows either the controller or system to power the LTC2978A. The DC1613 controller’s I2C/SMBus connections are opto-isolated from the PC’s USB port. The 3.
LTC2978A APPLICATIONS INFORMATION LTpowerPlay: AN INTERACTIVE GUI FOR POWER SYSTEM MANAGERS LTpowerPlay is a powerful Windows based development environment that supports Linear Technology Power System Manager ICs with EEPROM, including the LTC2978A 8-channel PMBus Power System Manager. The software supports a variety of different tasks. You can use LTpowerPlay to evaluate Linear Technology ICs by connecting to a demo board system.
LTC2978A APPLICATIONS INFORMATION PCB ASSEMBLY AND LAYOUT SUGGESTIONS The proposed stencil design enables out-gassing of the solder paste during reflow as well as regulating the finished solder thickness. See IPC7525A. Bypass Capacitor Placement The LTC2978A requires 0.1µF bypass capacitors between the VDD33 pins and GND, the VDD25 pin and GND, and the REFP pin and REFM pin. If the chip is being powered from the VPWR input, then that pin should also be bypassed to GND by a 0.1µF capacitor.
LTC2978A PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UP Package 64-Lead Plastic QFN (9mm × 9mm) (Reference LTC DWG # 05-08-1705 Rev C) 0.70 ±0.05 7.15 ±0.05 7.50 REF 8.10 ±0.05 9.50 ±0.05 (4 SIDES) 7.15 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 9 .00 ± 0.10 (4 SIDES) 0.75 ± 0.05 R = 0.10 TYP R = 0.115 TYP 63 64 0.40 ± 0.
LTC2978A REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 1/14 Improved the voltage range for ADC total unadjusted error (TUE) specification, voltage sense mode, from >1.8V to >1V 5 Added ADC TUE specification for Current Sense Mode 5 Consolidated previous ADC specifications—INL, DNL, voltage sense offset error, gain error—into TUE 5 Updated VOS_CMP offset voltage specification 7 VVOUT_ENn output high voltage specification: changed minimum from 11.
LTC2978A TYPICAL APPLICATION 0.1µF 5 VOUT 44 46 R32 R22 DC/DC CONVERTER VFB LOAD R12 RUN/SS SGND GND 47 45 6 50 48 49 51 IN 7 ASEL0 VIN_SNS ASEL1 VPWR VDD33 VDD33 WP GND DNC VOUT_EN0 VSENSEP6 VSENSEM1 VSENSEM6 VDACM1 VDACP2 VSENSEP5 VSENSEM2 VSENSEM5 VDACM2 VSENSEP4 VSENSEM3 VSENSEM4 VDACM3 12 3.