LTC2974 4-Channel PMBus Power System Manager Featuring Accurate Output Current Measurement Features Description n n n n n n n n n n n n n n n Sequence, Trim, Margin and Supervise Four Power Supplies Manage Faults, Monitor Telemetry and Create Fault Logs PMBus Compliant Command Set Supported by LTpowerPlayTM GUI Margin or Trim Supplies to 0.
LTC2974 Table of Contents Features............................................................ 1 Applications....................................................... 1 Typical Application............................................... 1 Description........................................................ 1 Absolute Maximum Ratings..................................... 4 Order Information................................................. 4 Pin Configuration.................................................
LTC2974 Table of Contents MFR_FAULTB0_RESPONSE and MFR_FAULTB1_ RESPONSE.................................................................60 Fault Warning and Status................................................ 61 CLEAR_FAULTS.......................................................... 61 STATUS_BYTE............................................................ 61 STATUS_WORD.......................................................... 62 STATUS_VOUT...........................................................
LTC2974 Absolute Maximum Ratings Pin Configuration (Note 1) 64 VSENSEM1 63 VSENSEP1 62 VSENSEM2 61 VSENSEP2 60 NC 59 NC 58 VDAC3 57 VDAC2 56 NC 55 NC 54 VDAC1 53 VDAC0 52 NC 51 NC 50 VSENSEM3 49 VSENSEP3 TOP VIEW VSENSEP0 1 VSENSEM0 2 VOUT_EN0 3 VOUT_EN1 4 VOUT_EN2 5 VOUT_EN3 6 AUXFAULTB 7 DNC 8 VIN_SNS 9 VPWR 10 VDD33 11 VDD33 12 VDD25 13 VDD25 14 TSENSE0 15 TSENSE1 16 48 ISENSEM3 47 ISENSEP3 46 ISENSEM2 45 ISENSEP2 44 ISENSEM1 43 ISENSEP1 42 ISENSEM0 41 ISENSEP0 40 REFM 39 GND 38 REFP 37 GND 36 ASEL1
LTC2974 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.
LTC2974 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.
LTC2974 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 tS_CS Update Rate CONDITIONS MIN TYP MAX 12.
LTC2974 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.
LTC2974 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.
LTC2974 Typical Performance Characteristics Reference Voltage vs Temperature ADC READ_VOUT Total Unadjusted Error vs Temperature ADC READ_IOUT Input Referred Offset Voltage vs Temperature 5 1.2320 0.06 4 1.2318 0.05 3 0.04 2 0.03 1 ERROR (%) 1.2316 1.2314 1.2312 1.2310 OFFSET (µV) 0.07 REFERENCE OUTPUT VOLTAGE (V) 1.2322 0.02 0.01 0 –1 0.00 –2 1.2308 –0.01 –3 1.2306 –0.02 THREE TYPICAL PARTS 1.2304 –50 –25 0 25 50 TEMPERATURE (°C) 100 75 –4 THREE TYPICAL PARTS –0.
LTC2974 Typical Performance Characteristics Voltage Supervisor Total Unadjusted Error vs Temperature 1.400 1.2 0.15 SUPERVISOR ERROR (%) SUPERVISOR ERROR (%) 1.405 1.4 HIGH RES MODE VIN = 1.5V 0.20 DAC Full-Scale Voltage vs Temperature, Gain = 0 0.10 0.05 0 –0.05 –0.10 DAC OUTPUT VOLTAGE (V) 0.25 Current Supervisor Total Unadjusted Error vs Temperature 1.0 50mV 0.8 0.6 0.4 20mV 0.2 –0.15 THREE TYPICAL PARTS –0.
LTC2974 Typical Performance Characteristics 0 VVOUT_ENn and VAUXFAULTB Output VOH vs Current Sourcing 14.0 OUTPUT HIGH VOLTAGE (V) OUTPUT VOLTAGE DELTA (ppm) 13.5 –1000 –2000 –3000 1.4 12.5 25°C 12.0 –40°C 1.0 11.5 11.0 10.5 0 10 20 30 40 LOAD CURRENT SOURCING (mA) 10.0 1 0 2 3 6 4 5 CURRENT SOURCING (µA) 7 2974 G19 1.6 1.4 1.4 1.2 1.2 1.0 1.0 VOL (V) VOL (V) 1.6 0.8 0.6 0 0 2 8 6 10 4 CURRENT SINKING (mA) 12 2974 G21 ALERTB VOL vs Current Sinking 0.
LTC2974 Pin Functions PIN NAME PIN NUMBER PIN TYPE DESCRIPTION VSENSEP0 1* In DC/DC Converter Differential (+) Output Voltage-0 Sensing Pin VSENSEM0 2* In DC/DC Converter Differential (–) Output Voltage-0 Sensing Pin VOUT_EN0 3 Out DC/DC Converter Enable-0 Pin. Output High Voltage Optionally Pulled-Up to 12V by 5µA VOUT_EN1 4 Out DC/DC Converter Enable-1 Pin. Output High Voltage Optionally Pulled-Up to 12V by 5µA VOUT_EN2 5 Out DC/DC Converter Enable-2 Pin.
LTC2974 Pin Functions PIN NAME PIN NUMBER PIN TYPE DESCRIPTION TSENSE3 34* In/Out ASEL0 35 In Ternary Address Select Pin 0 Input. Connect to VDD33, GND or Float to Encode 1 of 3 Logic States ASEL1 36 In Ternary Address Select Pin 1 Input. Connect to VDD33, GND or Float to Encode 1 of 3 Logic States GND 37 Ground REFP 38 Out GND 39 Ground REFM 40 Out Reference Return Pin. Needs 0.
LTC2974 Block Diagram 3.3V REGULATOR VOUT VIN VPWR 10 VDD33 VDD33(OUT) 11 2.
LTC2974 Operation LTC2974 Operation Overview The LTC2974 is a PMBus programmable power supply controller, monitor, sequencer and voltage and current supervisor that can perform the following operations: • Accept PMBus compatible programming commands. • Provide DC/DC converter input voltage, output voltage, output current, output temperature, and internal junction temperature readback through the PMBus interface.
LTC2974 Operation EEPROM The LTC2974 contains internal EEPROM (Non-Volatile Memory) to store configuration settings and fault log information. EEPROM endurance, retention and mass write operation time are specified over the operating temperature range. See Electrical Characteristics and Absolute Maximum Ratings sections. Non destructive operation above TJ = 85°C is possible although the Electrical Characteristics are not guaranteed and the EEPROM will be degraded.
LTC2974 Operation RESETB Holding the WDI/RESETB pin low for more than tRESETB will cause the LTC2974 to enter the power-on reset state. While in the power-on reset state, the device will not communicate on the I2C bus. Following the subsequent rising-edge of the WDI/RESETB pin, the LTC2974 will execute its power-on sequence per the user configuration stored in EEPROM. Connect WDI/RESETB to VDD33 with a 10k resistor.
LTC2974 Operation The LTC2974 always responds to its global address and the SMBus Alert Response address regardless of the state of its ASEL pins and the MFR_I2C_BASE_ADDRESS register. Processing Commands The LTC2974 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.
LTC2974 Operation Table 1.
LTC2974 Operation 1 S 7 1 1 8 1 SLAVE ADDRESS Wr A COMMAND CODE A 8 1 8 1 8 1 1 DATA BYTE LOW A DATA BYTE HIGH A PEC A P 2974 F06 Figure 6. Write Word Protocol with PEC 1 S 1 1 SLAVE ADDRESS Wr A COMMAND CODE A 7 1 1 8 P 2974 F07 Figure 7. Send Byte Protocol 1 S 7 1 1 8 1 SLAVE ADDRESS Wr A COMMAND CODE A 8 1 1 PEC A P 2974 F08 Figure 8.
LTC2974 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 command that supports paging. R/W Byte N Reg 0x00 28 OPERATION 0x01 Operating mode control. On/Off, Margin High and Margin Low. R/W Byte Y Reg Y 0x00 30 ON_OFF_CONFIG 0x02 CONTROL pin and PMBus on/off command setting.
LTC2974 PMBUS Command Summary Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE: DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE VOUT_UV_FAULT_RESPONSE 0x45 Action to be taken by the device when an output undervoltage fault is detected. R/W Byte Y Reg Y 0x7F 54 IOUT_OC_FAULT_LIMIT 0x46 Output overcurrent fault limit. R/W Word Y L11 Y 10.0 0xD280 46 IOUT_OC_FAULT_RESPONSE 0x47 Action to be taken by the device when an output overcurrent fault is detected.
LTC2974 PMBUS Command Summary Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE: DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE TON_DELAY 0x60 Time from CONTROL pin and/or OPERATION command = ON to VOUT_EN pin = ON. R/W Word Y L11 ms Y 1.0 0xBA00 51 TON_RISE 0x61 Time from when the VOUT_ENn pin goes high until the LTC2974 optionally softconnects its DAC and begins to servo the output voltage to the desired value. R/W Word Y L11 ms Y 10.
LTC2974 PMBUS Command Summary Summary Table DEFAULT VALUE: DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE COMMAND NAME CMD CODE DESCRIPTION USER_DATA_03 0xB3 Scratchpad location. R/W Word Y Reg USER_DATA_04 0xB4 Scratchpad location. R/W Word N MFR_LTC_RESERVED_1 0xB5 Manufacturer reserved. R/W Word Y MFR_T_SELF_HEAT 0xB8 Calculated temperature rise due to self-heating of output current sense device above value measured by external temperature sensor.
LTC2974 PMBUS Command Summary Summary Table COMMAND NAME CMD CODE DESCRIPTION TYPE DEFAULT VALUE: DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE MFR_CONFIG3_LTC2974 0xDA Configuration bits that are channel specific R/W Byte N Reg MFR_RETRY_DELAY 0xDB Retry interval during FAULT retry mode. R/W Word N L11 MFR_RESTART_DELAY 0xDC Delay from actual CONTROL active edge to virtual CONTROL active edge. R/W Word N MFR_VOUT_PEAK 0xDD Maximum measured value of READ_VOUT.
LTC2974 PMBUS Command Summary Summary Table CMD CODE DESCRIPTION COMMAND NAME TYPE DEFAULT VALUE: DATA FLOAT REF PAGED FORMAT UNITS EEPROM HEX PAGE MFR_COMMON 0xEF Manufacturer status bits that are common across multiple LTC chips. R Byte N Reg NA 61 MFR_IOUT_CAL_GAIN_TC 0xF6 Temperature coefficient applied to IOUT_ CAL_GAIN. R/W Word Y CF Y 0x0 46 MFR_RETRY_COUNT 0xF7 Retry count for all faulted off conditions that enable retry.
LTC2974 PMBus Command Description Addressing and Write Protect COMMAND NAME CMD CODE PAGE 0x00 Channel or page currently selected for any command that supports paging. R/W Byte N Reg WRITE_PROTECT 0x10 Level of protection provided by the device against accidental changes. R/W Byte N Reg MFR_I2C_BASE_ADDRESS 0xE6 Base value of the I2C/SMBus address byte. R/W Byte N MFR_PAGE_FF_MASK 0xE4 Configuration defining which channels respond to global page commands (PAGE=0xFF).
LTC2974 PMBus Command Description WRITE_PROTECT Data Contents BIT(S) SYMBOL OPERATION b[7:0] Write_protect[7:0] 1000_0000b: Level 1 Protection - Disable all writes except to the WRITE_PROTECT, PAGE, MFR_EE_UNLOCK, and STORE_ USER_ALL commands. 0100_0000b: Level 2 Protection – Disable all writes except to the WRITE_PROTECT, PAGE, MFR_EE_UNLOCK, STORE_ USER_ALL, OPERATION, MFR_PAGE_FF_MASK and CLEAR_FAULTS commands. 0000_0000b: Enable writes to all commands. xxxx_xxxxb: All other values reserved.
LTC2974 PMBus Command Description On/Off Control, Margining and Configuration COMMAND NAME CMD CODE OPERATION 0x01 Operating mode control. On/Off, Margin High and Margin Low. R/W Byte Y Reg Y 0x00 30 ON_OFF_CONFIG 0x02 CONTROL pin and PMBus on/off command setting. R/W Byte Y Reg Y 0x12 31 MFR_CONFIG_LTC2974 0xD0 Configuration bits that are channel specific.
LTC2974 PMBus Command Description OPERATION Data Contents (On_off_config_use_pmbus=0) On or Off SYMBOL Action Operation_control[1:0] Operation_margin[1:0] Operation_fault[1:0] Reserved (read only) b[7:6] b[5:4] b[3:2] b[1:0] Output at nominal 00, 01 or 10 00 XX 00 Margin low (ignore faults and warnings) 00, 01 or 10 01 01 00 BITS FUNCTION Margin low 00, 01 or 10 01 10 00 Margin high (ignore faults and warnings 00, 01 or 10 10 01 00 Margin high 00, 01 or 10 10 10 00 Reser
LTC2974 PMBus Command Description MFR_CONFIG_LTC2974 This command is used to configure various manufacturer specific operating parameters for each channel. MFR_CONFIG_LTC2974 Data Contents BIT(S) SYMBOL OPERATION b[15] Reserved Don’t care. Always returns 0. b[14] Mfr_config_cascade_on Configures channel’s control pin for cascade sequence ON. There is no provision for cascade sequence OFF. See description for time based sequence OFF options.
LTC2974 PMBus Command Description MFR_CONFIG_LTC2974 Data Contents BIT(S) b[1] SYMBOL OPERATION Mfr_config_dac_gain DAC buffer gain. 0: Select DAC buffer gain dac_gain_0 (1.38V full-scale) 1: Select DAC buffer gain dac_gain_1 (2.65V full-scale) b[0] Mfr_config_ dac_pol DAC output polarity. 0: Encodes negative (inverting) DC/DC converter trim input. 1: Encodes positive (non-inverting) DC/DC converter trim input.
LTC2974 PMBus Command Description be used to turn all cascade channels off then on to clear the faulted off state when the slave’s control pin is low. For this reason we refer to the control pin as being redefined as a sequence pin. The waveform of Figure 16 illustrates cascade sequence ON and time based sequence OFF using the configuration illustrated in Figure 15. In this example the FAULTB0 pin is used as a broadcast off signal.
LTC2974 PMBus Command Description MFR_CONFIG2_LTC2974 This command register determines whether VOUT overvoltage or overcurrent faults from a given channel cause the AUXFAULTB pin to be pulled low. MFR_CONFIG2_LTC2974 Data Contents BIT(S) SYMBOL b[7] Mfr_auxfaultb_oc_fault_response_ chan3 OPERATION Response to channel 3 IOUT_OC_FAULT. 1 = Pull AUXFAULTB low via fast pull-down. 0 = Do not pull AUXFAULTB low. b[6] Mfr_auxfaultb_oc_fault_response_ chan2 Response to channel 2 IOUT_OC_FAULT.
LTC2974 PMBus Command Description b[5] Mfr_auxfaultb_uc_fault_response_ chan1 Response to channel 1 IOUT_UC_FAULT. 1 = Pull AUXFAULTB low via fast pull-down. 0 = Do not pull AUXFAULTB low. b[4] Mfr_auxfaultb_uc_fault_response_ chan0 Response to channel 0 IOUT_UC_FAULT. 1 = Pull AUXFAULTB low via fast pull-down. 0 = Do not pull AUXFAULTB low. b[3] Mfr_track_en_chan3 Select if channel 3 is a slave in a tracked power supply system. 0: Channel is not a slave in a tracked power supply system.
LTC2974 PMBus Command Description Tracking Supplies On and Off The LTC2974 supports tracking power supplies that are equipped with a tracking pin and configured for tracking. A tracking power supply uses a secondary feedback terminal (TRACK) to allow its output voltage to be scaled to an external master voltage. Typically the external voltage is generated by the supply with the highest voltage in the system, which is fed to the slave track pins (see Figure 17).
LTC2974 PMBus Command Description TON_RISE EXPIRES FOR ALL CHANNELS. UV AND UC DETECT ENABLED ON ALL CHANNELS TOFF_DELAY ENTERED FOR ALL CHANNELS. UV AND UC DETECT DISABLED ON ALL CHANNELS VOUT0 VOUT1 VOUT2 UV FAULT ON CHANNEL 1 BRINGS DOWN MASTER VIA FAULTB0.
LTC2974 PMBus Command Description The following example illustrates configuring an LTC2974 with one master channel and three slaves.
LTC2974 PMBus Command Description MFR_CONFIG_ALL_LTC2974 Data Contents BIT(S) b[7] SYMBOL OPERATION Mfr_config_all_fault_log_enable Enable fault logging to EEPROM in response to Fault. 0: Fault logging to EEPROM is disabled. 1: Fault logging to EEPROM is enabled. b[6] Mfr_config_all_vin_on_clr_faults_en Allow VIN rising above VIN_ON to clear all latched faults. 0: VIN_ON clear faults feature is disabled. 1: VIN_ON clear faults feature is enabled.
LTC2974 PMBus Command Description STORE_USER_ALL and RESTORE_USER_ALL STORE_USER_ALL, RESTORE_USER_ALL commands provide access to User EEPROM space. Once a command is stored in User EEPROM, it will be restored with explicit restore command or when the part emerges from power-on reset after power is applied. While either of these commands is being processed, the part will indicate it is busy, see Response When Part Is Busy on page 43. STORE_USER_ALL.
LTC2974 PMBus Command Description MFR_EE_UNLOCK Data Contents BIT(S) SYMBOL OPERATION b[7:0] Mfr_ee_unlock[7:0] To unlock user EEPROM space for Mfr_ee_erase and Mfr_ee_data read or write operations with PEC allowed: Write 0x2b followed by 0xd4. To unlock user EEPROM space for Mfr_ee_erase and Mfr_ee_data read or write operations with PEC required: Write 0x2b followed by 0xd5.
LTC2974 PMBus Command Description MFR_EE_DATA Data Contents BIT(S) SYMBOL OPERATION b[7:0] Mfr_ee_data[7:0] To read user space 1) Use the appropriate Mfr_ee_unlock sequence to configure for Mfr_ee_data commands with or without PEC. 2) Read Mfr_ee_data[0] = PackingId (MFR Specific ID). 3) Read Mfr_ee_data[1] = NumberOfUserWords (total number of 16-bit word available).
LTC2974 PMBus Command Description Output Voltage Commands and Limits COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM VOUT_MODE 0x20 Output voltage data format and mantissa exponent (2–13). R Byte Y Reg VOUT_COMMAND 0x21 Servo target. Nominal DC/DC converter output voltage setpoint. R/W Word Y L16 V VOUT_MAX 0x24 Upper limit on the output voltage the unit can command regardless of any other commands.
LTC2974 PMBus Command Description VOUT_COMMAND, VOUT_MAX, VOUT_MARGIN_HIGH, VOUT_MARGIN_LOW, VOUT_OV_FAULT_LIMIT, VOUT_OV_WARN_LIMIT, VOUT_UV_WARN_LIMIT, VOUT_UV_FAULT_LIMIT, POWER_GOOD_ON and POWER_GOOD_OFF These commands provide various servo, margining and supervising limits for a channel’s output voltage. MFR_VOUT_DISCHARGE_THRESHOLD This register contains the coefficient that multiplies VOUT_COMMAND in order to determine the OFF threshold voltage for the associated output.
LTC2974 PMBus Command Description Output Current Commands and Limits CMD CODE DESCRIPTION COMMAND NAME TYPE PAGED FORMAT UNITS EEPROM DEFAULT REF VALUE PAGE IOUT_CAL_GAIN 0x38 The nominal resistance of the current sense element in mΩ. R/W Word Y L11 mΩ Y 1.0 0xBA00 46 IOUT_OC_FAULT_LIMIT 0x46 Output overcurrent fault limit. R/W Word Y L11 A Y 10.0 0xD280 47 IOUT_OC_WARN_LIMIT 0x4A Output overcurrent warning limit. R/W Word Y L11 A Y 5.
LTC2974 PMBus Command Description IOUT_OC_FAULT_LIMIT, IOUT_OC_WARN_LIMIT and IOUT_UC_FAULT_LIMIT IOUT supervisor fault and warning limits. IOUT_OC_FAULT_LIMITED is internally limited to values greater or equal to zero. The register readback value always returns what was last written and does not reflect internal limiting. IOUT_UC_FAULT_LIMITED is internally limited to values less than zero. The register readback value always returns what was last written and does not reflect internal limiting.
LTC2974 PMBus Command Description External Temperature Commands And Limits COMMAND NAME CMD CODE DESCRIPTION OT_FAULT_LIMIT 0x4F Overtemperature fault limit setting for the external temperature sensor. R/W Word Y L11 °C Y 65.0 0xEA08 48 OT_WARN_LIMIT 0x51 Overtemperature warning limit for the external temperature sensor R/W Word Y L11 °C Y 60.0 0xE3C0 48 UT_WARN_LIMIT 0x52 Undertemperature warning limit for the external temperature sensor.
LTC2974 PMBus Command Description MFR_T_SELF_HEAT, MFR_IOUT_CAL_GAIN_TAU_INV and MFR_IOUT_CAL_GAIN_THETA The LTC2974 uses an innovative (patent pending) algorithm to dynamically model the temperature rise from the external temperature sensor to the inductor core. This temperature rise is called MFR_T_SELF_HEAT and is used to calculate the final temperature correction required by IOUT_CAL_GAIN.
LTC2974 PMBus Command Description Initially self heat is set to zero. After each temperature measurement self heat is updated to be the previous value of self heat incremented or decremented by ∆MFR_T_SELF_HEAT. The actual value of Cτ is not required. The important quantity is the thermal time constant τINV = (θIS Cτ). For example, if an inductor has a thermal time constant τINV = 5 seconds then: MFR_IOUT_CAL_GAIN_TAU_INV = (4 • tCONV_SENSE)/5 = 4 • 66ms/5s = 0.
LTC2974 PMBus Command Description Sequencing Timing Limits and Clock Sharing COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM DEFAULT REF VALUE PAGE TON_DELAY 0x60 Time from CONTROL pin and/or OPERATION command = ON to VOUT_EN pin = ON. R/W Word Y L11 ms Y 1.0 0xBA00 51 TON_RISE 0x61 Time from when the VOUT_ENn pin goes high until the LTC2974 optionally soft-connects its DAC and begins to servo the output voltage to the desired value. R/W Word Y L11 ms Y 10.
LTC2974 PMBus Command Description Clock Sharing Multiple LTC PMBus devices can synchronize their clocks in an application by connecting together the open-drain SHARE_CLK input/outputs to a pull-up resistor as a wired OR. In this case the fastest clock will take over and synchronize all other chips to its falling edge. SHARE_CLK can optionally be used to synchronize ON/OFF dependency on VIN across multiple chips by setting the Mfr_config_all_vin_share_enable bit of the MFR_CONFIG_ALL register.
LTC2974 PMBus Command Description b[1] Mfr_pwrgd_en_chan1 Channel 1. 1 = PWRGD status for this channel is ANDed with PWRGD status for any similarly enabled channels to determine when the PWRGD pin gets asserted. 0 = PWRGD status for this channel does not affect the PWRGD pin. b[0] Mfr_pwrgd_en_chan0 Channel 0. 1 = PWRGD status for this channel is ANDed with PWRGD status for any similarly enabled channels to determine when the PWRGD pin gets asserted.
LTC2974 PMBus Command Description Fault Responses COMMAND NAME CMD CODE DESCRIPTION VOUT_OV_FAULT_RESPONSE 0x41 Action to be taken by the device when an output overvoltage fault is detected. R/W Byte Y Reg Y 0x80 55 VOUT_UV_FAULT_RESPONSE 0x45 Action to be taken by the device when an output undervoltage fault is detected. R/W Byte Y Reg Y 0x7F 55 IOUT_OC_FAULT_RESPONSE 0x47 Action to be taken by the device when an output overcurrent fault is detected.
LTC2974 PMBus Command Description 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. Note that in addition to the response described by these commands, the LTC2974 will also: • Set the appropriate bit(s) in the STATUS_BYTE. • Set the appropriate bit(s) in the STATUS_WORD.
LTC2974 PMBus Command Description IOUT_OC_FAULT_RESPONSE and IOUT_UC_FAULT_RESPONSE The fault response documented here is for currents that are measured by the high speed supervisor. These currents are measured over a short period of time and may require a deglitch period. Note that in addition to the response described by these commands, the LTC2974 will also: • Set the appropriate bit in the STATUS_BYTE. • Set the appropriate bit in the STATUS_WORD.
LTC2974 PMBus Command Description 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. Note that in addition to the response described by these commands, the LTC2974 will also: • Set the appropriate bit(s) in the STATUS_BYTE. • Set the appropriate bit(s) in the STATUS_WORD.
LTC2974 PMBus Command Description TON_MAX_FAULT_RESPONSE This command defines the LTC2974 response to a TON_MAX_FAULT. It may be used to protect against a short-circuited output at startup. After startup use VOUT_UV_FAULT_RESPONSE to protect against a short-circuited output. The device also: • Sets the HIGH_BYTE bit in the STATUS_BYTE, • Sets the VOUT bit in the STATUS_WORD, • Sets the TON_MAX_FAULT bit in the STATUS_VOUT register, and • Notifies the host by asserting ALERTB.
LTC2974 PMBus Command Description Shared External Faults COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM DEFAULT REF VALUE PAGE MFR_FAULTB0_PROPAGATE 0xD2 Configuration that determines if a channels faulted off state is propagated to the FAULTB0 pin. R/W Byte Y Reg Y 0x00 59 MFR_FAULTB1_PROPAGATE 0xD3 Configuration that determines if a channels faulted off state is propagated to the FAULTB1 pin.
LTC2974 PMBus Command Description MFR_FAULTB0_RESPONSE and MFR_FAULTB1_RESPONSE These manufacturer specific commands share the same format and specify the response to assertions of the FAULTB pins. MFR_FAULTB0_RESPONSE determines which channels shut off when the FAULTB0 pin is asserted low and MFR_FAULTB1_RESPONSE determines which channels shut off when the FAULTB1 pin is asserted low.
LTC2974 PMBus Command Description Fault Warning and Status COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM DEFAULT REF VALUE PAGE CLEAR_FAULTS 0x03 Clear any fault bits that have been set. Send Byte Y NA 61 STATUS_BYTE 0x78 One byte summary of the unit’s fault condition. R Byte Y Reg NA 61 STATUS_WORD 0x79 Two byte summary of the unit’s fault condition. R Word Y Reg NA 62 STATUS_VOUT 0x7A Output voltage fault and warning status.
LTC2974 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.
LTC2974 PMBus Command Description STATUS_IOUT The STATUS_IOUT command returns the summary of the output current faults or warnings which have occurred, as shown in the following table: STATUS_IOUT Data Contents BIT(S) SYMBOL OPERATION b[7] Status_iout_oc_fault Overcurrent fault. b[6] Status_iout_oc_uv_fault Not Supported. Always returns 0. b[5] Status_iout_oc_warn Overcurrent warning b[4] Status_iout_uc_fault Undercurrent fault. b[3] Status_iout_curr_share_fault Not Supported.
LTC2974 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 b[7] Status_cml_cmd_fault OPERATION 1 = An illegal or unsupported command fault has occurred. 0 = No fault has occurred. b[6] Status_cml_data_fault 1 = Illegal or unsupported data received. 0 = No fault has occurred.
LTC2974 PMBus Command Description b[2] Status_mfr_dac_saturated A previous servo operation terminated with maximum or minimum DAC value. Current Page Yes No No b[1] Status_mfr_auxfaultb_faulted_off AUXFAULTB has been de-asserted due to a VOUT or IOUT fault. All No No No b[0] Status_mfr_watchdog_fault 1 = A watchdog fault has occurred. All Yes Yes No 0 = No watchdog fault has occurred. MFR_PADS The MFR_PADS command provides read-only access of digital pads (pins).
LTC2974 PMBus Command Description This is the only command that may still be read when the LTC2974 is busy processing an EEPROM or other command. It may be polled by the host to determine when the LTC2974 is available to process a PMBus command. A busy device will always acknowledge its address but will NACK the command byte and set Status_byte_busy and Status_word_busy when it receives a command that it cannot immediately process. ALERTB will not be asserted low in this case.
LTC2974 PMBus Command Description READ_VIN This command returns the most recent ADC measured value of the input voltage at the VIN_SNS pin. READ_VOUT This command returns the most recent ADC measured value of the channel’s output voltage. READ_IOUT This command returns the most recent ADC measured value of the channel’s output current. READ_TEMPERATURE_1 This command returns the most recent measured value of the external diode temperature in °C.
LTC2974 PMBus Command Description MFR_READ_IOUT Data Contents BIT(S) SYMBOL b[15:0] Mfr_read_iout[15:0] OPERATION Channel output current expressed in custom format for improved resolution at high currents. Value = Y • 2.5 where Y = b[15:0] is a signed two’s-complement number. Example: MFR_READ_IOUT = 5mA For b[15:0] = 0x0002 Value = 2 • 2.5 = 5mA The granularity of the returned value is always 2.5mA, and the return value is limited to ±81.92A. Use the READ_IOUT command for larger currents.
LTC2974 PMBus Command Description MFR_VIN_PEAK This command returns the maximum ADC measured value of the input voltage. This register is reset to 0x7C00 (–225) when the LTC2974 emerges from power-on reset or when a CLEAR_FAULTS command is executed. MFR_VOUT_PEAK This command returns the maximum ADC measured value of the channel’s output voltage. This register is reset to 0xF800 (0.0) when the LTC2974 emerges from power-on reset or when a CLEAR_FAULTS command is executed.
LTC2974 PMBus Command Description Fault Logging COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM DEFAULT REF VALUE PAGE Send Byte N NA 70 MFR_FAULT_LOG_RESTORE 0xEB Command a transfer of the fault log previously stored in EEPROM back to RAM. Send Byte N NA 70 MFR_FAULT_LOG_CLEAR 0xEC Initialize the EEPROM block reserved for fault logging and clear any previous fault logging locks. Send Byte N NA 71 MFR_FAULT_LOG_STATUS 0xED Fault logging status.
LTC2974 PMBus Command Description MFR_FAULT_LOG_CLEAR This command initializes the EEPROM block reserved for fault logging. Any previous fault log stored in EEPROM will be erased by this operation and logging of the fault log RAM to EEPROM will be enabled. Make sure that Mfr_fault_ log_status_ram = 0 before issuing the MFR_FAULT_LOG_CLEAR command. MFR_FAULT_LOG_STATUS This register is used to manage fault log events.
LTC2974 PMBus Command Description Table 2. Data Block Contents Table 2. Data Block Contents DATA DATA Position_last[7:0] SharedTime[7:0] BYTE* DESCRIPTION 0 1 BYTE* DESCRIPTION Position of fault log pointer when fault occurred. Mfr_temperature_peak2[7:0] 39 41-bit share-clock counter value when fault occurred. Counter LSB is in 200μs increments.
LTC2974 PMBus Command Description Table 2.
LTC2974 PMBus Command Description MFR_FAULT_LOG Read Example PREAMBLE INFORMATION The following table fully decodes a sample fault log read with Position_last = 13 to help clarify the cyclical nature of the operation. Data Block Contents PREAMBLE INFORMATION BYTE BYTE NUMBER NUMBER DECIMAL HEX 0 00 DATA DESCRIPTION Position_last[7:0] = 13 Position of faultlog pointer when fault occurred.
LTC2974 PMBus Command Description PREAMBLE INFORMATION CYCLICAL MUX LOOP DATA BYTE BYTE NUMBER NUMBER DECIMAL HEX LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL DATA DESCRIPTION MUX LOOP 1 60 3C Status_iout0[7:0] 61 3D Status_ temperature0[7:0] 85 55 53 Read_pout3[15:8] 86 56 52 Read_pout3[7:0] 62 3E Status_vout1[7:0] 87 57 51 Read_iout3[15:8] 63 3F Status_iout1[7:0] 88 58 50 Read_iout3[7:0] 64 40 Status_ temperature1[7:0] 89 59 49 Status_iout3[7:0] 90
LTC2974 PMBus Command Description CYCLICAL MUX LOOP DATA CYCLICAL MUX LOOP DATA LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL MUX LOOP 1 54 BYTES PER LOOP MUX LOOP 2 116 74 22 Read_ temperature_1_1[7:0] 144 90 48 Status_ temperature3[7:0] 117 75 21 Status_mfr_ specific1[7:0] 145 91 47 Read_ temperature_1_3[15:8] 118 76 20 Status_vout1[7:0] 146 92 46 119 77 19 Read_vout1[15:8] Read_ temperature_1_3[7
LTC2974 PMBus Command Description CYCLICAL MUX LOOP DATA CYCLICAL MUX LOOP DATA LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL 174 MUX LOOP 2 AE 18 Read_vout1[7:0] 175 AF 17 0x0 176 B0 16 Status_input[7:0] 177 B1 15 Read_vin[15:8] 178 B2 14 Read_vin[7:0] 179 B3 13 Read_pout0[15:8] 180 B4 12 Read_pout0[7:0] 181 B5 11 Read_iout0[15:8] 182 B6 10 Read_iout0[7:0] 183 B7 9 Status_iout0[7:0] 184
LTC2974 PMBus Command Description CYCLICAL MUX LOOP DATA LOOP BYTE BYTE BYTE NUMBER NUMBER NUMBER DECIMAL HEX DECIMAL MUX LOOP 3 54 BYTES PER LOOP 233 E9 13 Read_pout0[15:8] 234 EA 12 Read_pout0[7:0] 235 EB 11 Read_iout0[15:8] 236 EC 10 Read_iout0[7:0] 237 ED 9 Status_iout0[7:0] Last valid fault log byte 238 EE 0x00 Bytes EE - FE return 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 247 F7 0x00 248
LTC2974 PMBus Command Description CAPABILITY The CAPABILITY command provides a way for a host system to determine some key capabilities of the LTC2974. CAPABILITY Data Contents BIT(S) SYMBOL b[7] Capability_pec b[6:5] Capability_scl_max b[4] OPERATION Hard coded to 1 indicating Packet Error Checking is supported. Reading the Mfr_config_all_pec_en bit will indicate whether PEC is currently required. Hard coded to 01b indicating the maximum supported bus speed is 400kHz.
LTC2974 Applications Information Overview The LTC2974 is a power management IC that is capable of sequencing, margining, trimming, supervising output voltage for OV/UV conditions, supervising output current for OC/UC conditions, fault management, and voltage/ current/temperature readback for four DC/DC converter channels. Input voltage and LTC2974 junction temperature readback are also available.
LTC2974 Applications Information a channel will wait following the start of an ON sequence before its VOUT_EN pin will enable a DC/DC converter. Once the DC/DC converter has been enabled, the TON_RISE value determines the time at which the device soft-connects the DAC and servos the DC/DC converter output to the VOUT_COMMAND value. The TON_MAX_FAULT_LIMIT value determines the time at which the device checks for an undervoltage condition.
LTC2974 Applications Information DAC Modes VOUT Off Threshold Voltage The DACs that drive the VDACn pins can operate in several useful modes. See MFR_CONFIG_LTC2974. The MFR_VOUT_DISCHARGE_THRESHOLD command register allows the user to specify the OFF threshold that the output voltage must decay below before the channel can enter/re-enter the ON state. The OFF threshold voltage is specified by multiplying MFR_VOUT_DISCHARGE_ THRESHOLD and VOUT_COMMAND.
LTC2974 Applications Information OV/UV faults. In addition, the high-speed current supervisor OC and UC fault thresholds are configured using the IOUT_OC_FAULT_LIMIT and IOUT_UC_FAULT_LIMIT commands, respectively. The IOUT_OC_FAULT_RESPONSE and IOUT_UC_FAULT_RESPONSE commands determine the responses to OC/UC faults.
LTC2974 Applications Information Multi-Channel Fault Management Multi-channel fault management is handled using the bidirectional FAULTB pins. Figure 28 illustrates the connections between channels and the FAULTB pins. • The MFR_FAULTBn_PROPAGATE register acts like a programmable switch that allows faulted_off conditions from a particular channel (PAGE) to propagate to either FAULTB output.
LTC2974 Applications Information TO VIN OF DC/DCs TO HOST CONTROLLER TO INPUT SWITCH LTC2974 #1 VIN_SNS AUXFAULTB LTC2974 #n VIN_SNS AUXFAULTB SDA SCL ALERTB CONTROL0 SDA SCL ALERTB CONTROL0 WDI/RESETB FAULTB0 WDI/RESETB FAULTB0 SHARE_CLK PWRGD SHARE_CLK PWRGD GND GND TO OTHER LTC2974s–10k EQUIVALENT PULL-UP RECOMMENDED ON EACH LINE EXCEPT SHARE_CLK (USE 5.49k) 2974 F29 Figure 29.
LTC2974 Applications Information VIN 4.5V < VIBUS < 15V VPWR 0.1µF VIN_SNS VOUT VDAC0 VDD33 VDD33 VDD25 LTC2974* R20 VFB LOAD R10 VDD25 0.1µF DC/DC CONVERTER R30 VSENSEP0 VSENSEM0 SGND VOUT_EN0 RUN/SS GND GND 2974 F31 *SOME DETAILS OMITTED FOR CLARITY ONLY ONE OF FOUR CHANNELS SHOWN Figure 31. Application Circuit for DC/DC Converters with External Feedback Resistors state.
LTC2974 Applications Information VIN 4.5V < VIBUS < 15V 0.1µF VPWR VIN_SNS VDD33 VSENSEP0 VDAC0 VDD33 VDD25 0.1µF R30 LTC2974* LOAD VDD25 VO+ TRIM VSENSE+ DC/DC CONVERTER VSENSEM0 VSENSE– VOUT_EN0 ON/OFFB VO– GND 2974 F32 *SOME DETAILS OMITTED FOR CLARITY ONLY ONE OF FOUR CHANNELS SHOWN Figure 32.
LTC2974 Applications Information Measuring Current with a Sense Resistor A circuit for measuring current with a sense resistor is shown in Figure 33. The balanced filter rejects both common mode and differential mode noise from the output of the DC/DC converter. The filter is placed directly across the sense resistor in series with the DC/DC converter’s inductor. Note that the current sense inputs must be limited to less than 6V with respect to ground.
LTC2974 Applications Information SWX1 RCM1 RCM1 RCM2 CCM2 RCM1 L CCM2 ISENSEP LTC2974 ISENSEM DCR 2974 F35 RCM1/3 RCM2 CCM1 DCR L CCM2 DCR L TO LOAD SWX2 SWX3 Figure 35. Multiphase DCR Current Sensing Circuits Multiphase Design Example Sensing Negative Voltages Using the same values for inductance and DCR from the previous design example, the value for RCM1 will be 3kΩ for a three phase DC/DC converter if CCM1 is left at 220nF. Similarly, the value for IOUT_CAL_GAIN will be DCR/3 = 3.
LTC2974 Applications Information 4.5V < VIBUS < 15V VIN_SNS VPWR LTC2974 1.23V TYP REFP 0.1µF SDA PMBus INTERFACE SCL ALERTB CONTROL REFM VSENSEP1 1µA AT 0.5V 0.1µF R1 = 4.99k VSENSEM1 R2 = 120k WDI/RESETB VEE = –12V FAULTB SHARE_CLK ASEL0 PWRGD ASEL1 WP GND WDI/RESETB 2974 F37 POWER_GOOD_ON = 0.5V FOR VEE POWER_GOOD = –11.414V WHERE VEE POWER_GOOD = VREFP – POWER_GOOD_ON (R2/R1 + 1) – 1µA • R2 ONLY ONE OF FOUR CHANNELS SHOWN, SOME DETAILS OMITTED FOR CLARITY Figure 37.
LTC2974 Applications Information REPEAT OUTLINED CIRCUIT FOR EVERY LTC2974 150k 49.9k 4.5V TO 15V VPWR 0.1µF LTC2974* Si1303 ISOLATED 3.3V VDD33 SCL 0.1µF GND VDD33 SDA 0.1µF VDD25 TO DC1613 I2C/SMBUS/PMBUS CONTROLLER VDD25 10k 10k 5.49k SCL SDA SHARE_CLK WP GND 2974 F38 *PIN CONNECTIONS OMITTED FOR CLARITY TO/FROM OTHER LTC2974s Figure 38. DC1613 Controller Connections When VPWR Is Used TP0101K-SOT23 SYSTEM 3.3V OR’D 3.3V 0.
LTC2974 Applications Information Accurate DCR Temperature Compensation Using the DC resistance of the inductor as a current shunt element has several advantages – no additional power loss, lower circuit complexity and cost. However, the strong temperature dependence of the inductor resistance and the difficulty in measuring the exact inductor core temperature introduce errors in the current measurement. For copper, a change of inductor temperature of only 1°C corresponds to approximately 0.
LTC2974 Applications Information The inductor resistance, RK = VDCR(K)/IOUT(K), power dissipation PK = VDCR(K) IOUT(K) and the sensed temperature TK, (K = 1, 2) are recorded for each load current. To increase the accuracy in calculating θIS, the two load currents should be chosen around I1 = 10% and I2 = 90% of the current range of the system. The inductor thermal time constant τ models the first order thermal response of the inductor and allows accurate DCR compensation during load transients.
LTC2974 Applications Information PCB Assembly and Layout Suggestions Bypass Capacitor Placement The LTC2974 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. In order to be effective, these capacitors should be made of a high quality ceramic dielectric such as X5R or X7R and be placed as close to the chip as possible.
LTC2974 Applications Information VSENSEP 100k QFN PACKAGE LTC2974 APERATURE DESIGN 50% TO 80% REDUCTION GROUND PLANE VSENSEM 100k 2974 F41 Figure 41. Connecting Unused Inputs to GND prevent loading of the filter. The temperature sense inputs (TSENSEn) may be left floating. The temperture reported on floating TSENSEn inputs will be the internal die temperature (READ_TEMPERATURE_2).
LTC2974 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.
LTC2974 Revision History REV DATE DESCRIPTION PAGE NUMBER A 5/13 Title, Features and Description revised. Added specifications: tINIT, tUPDATE_ADC, tOFF_MIN. 6 Curve G08: Corrected Y-axis units from mA to µA. 10 Block Diagram revised. 15 RESETB section: Clarified I2C disabled, 10k resistor and capacitance. 18 24, 51 Changed data format for MFR_DAC and MFR_I2C_BASE_ADDRESS to Reg from U16. Changed default value for MFR_SPECIAL_ID to 0x0213 from 0x0212.
LTC2974 Typical Application 0.1µF 3.3V MMBT3906 TSENSE0 NC DNC NC 51 52 55 56 59 60 8 NC 35 NC 36 NC 10 NC 12 ASEL0 11 VPWR 14 VDD33 13 VDD25 GND WP 28 VDD33 15 TG 65 VDD25 VIN VIN_SNS 9 330nF ASEL1 0.1µF TSENSE2 330nF 27 MMBT3906 SWX 53 1 VDAC0 VDAC2 VSENSEP0 VSENSEP2 57 61 BG 2 42 41 3 VSENSEM0 VSENSEM2 ISENSEM0 ISENSEM2 ISENSEP0 ISENSEP2 VOUT_EN0 VOUT_EN2 GND 38 0.
