7 PMBus Commands

OPERATION (0x01)

The OPERATION command is used to turn the device output ON or OFF. It is also used to set the output voltage to the upper or lower MARGIN voltages.

Bit [7]: Controls if PMBus device output is ON or OFF

• 0 : Output is OFF
• 1 : Output is ON

Bit [6]: Controls the power down behavior

• 0 : Output is turned OFF immediately
• 1 : The device is powered down following the values set in the TOFF_DELAY and TOFF_FALL commands

Bit [5:4]: Voltage command source

• 00 : The nominal output voltage is set by the PMBus VOUT_COMMAND data
• 01 : The nominal output voltage is set by the PMBus VOUT_MARGIN_LOW data
• 10 : The nominal output voltage is set by the PMBus VOUT_MARGIN_HIGH data
• 11 : AVS Bus (AVS Bus not supported)

Bit [3:2]: Margin fault response

• 00 : Invalid
• 01 : The faults caused by VOUT_MARGIN_HIGH or VOUT_MARGIN_LOW are ignored
• 10 : The faults caused by VOUT_MARGIN_HIGH or VOUT_MARGIN_LOW are acted upon
• 11 : Invalid

Bit [1]: Transition control (AVS Bus not implemented)

Bit [0]: Reserved

ON_OFF_CONFIG (0x02)

Bit [7:5]: Reserved

Bit [4]: Sets the default to either operate when power is present or for the ON/OFF to be controlled by serial bus commands

• 0 : Device powers up when the power is present
• 1 : Device does not power up until commanded by the OPERATION command

Bit [3]: Controls how the unit responds to commands received via the serial bus

• 0 : Device ignores the ON/OFF portion of the OPERATION command from serial bus
• 1 : Device requires the ON/OFF portion of the OPERATION command

Bit [2]: Controls how the unit responds to the EN pin

• 0 : Unit ignores the EN pin (ON/OFF controlled only the OPERATION command)
• 1 : Unit requires the EN pin to be asserted to start the unit

Bit [1]: Polarity of the EN pin

• 0 : Active low
• 1 : Active high

Bit [0]: EN pin action

• 0 : Use the programmed turn OFF delay and fall time
• 1 : Turn OFF the output and stop transferring energy to the output as fast as possible

CLEAR_FAULTS (0x03)

The CLEAR_FAULTS command is used to clear any fault bits that have been set. This command clears all bits in all status registers simultaneously. At the same time, the device releases its SMBALERT signal output if the device is asserting the SMBALERT signal. The CLEAR_FAULTS command does not cause a unit that has latched off for a fault condition to restart. If the fault is still present when the bit is cleared, the fault bit is immediately reset and the host notified by the usual means.

WRITE_PROTECT (0x10)

Bit [7]: Control writing to the PMBus device for protection against accidental changes

• 0 : Enable all writes as permitted in bit 5 or bit 6
• 1 : Disable all writes except the WRITE_PROTECT command (bit 5 and bit 6 must be 0)

Bit [6]: Control writing to the PMBus device for protection against accidental changes

• 0 : Enable all writes as permitted in bit 5 or bit 7
• 1 : Disable all writes except for the WRITE_PROTECT, and OPERATION commands (bit 5 and bit 7 must be 0)

Bit [5]: Control writing to the PMBus device for protection against accidental changes

• 0 : Enable all writes as permitted in bit 6 or bit 7
• 1 : Disable all writes except the WRITE_PROTECT, OPERATION, ON_OFF_CONFIG, and VOUT_COMMAND. (bit 6 and bit 7 must be 0)

Bit [4:0]: Reserved

STORE_USER_ALL (0x15)

The STORE_USER_ALL command stores all of the current storable register settings in the EEPROM memory as the new defaults on power up. It is permissible to use this command while the device is switching. To use this command:

1. Set all settings to the desired power up configuration.
2. Pull EN low to disable switching.
3. Apply 7.5 ± 0.25V to the VIN pin
4. Execute the command.
5. Execute a RESTORE_USRE_ALL command..
6. Compare the settings in the part values with the expected settings. If they differ, repeat this procedure. If the settings differ a second time, discard the part.

RESTORE_USER_ALL (0x16)

The RESTORE_USER_ALL command restores all of the storable register settings from EEPROM memory to those registers which are unprotected. This command should not be used while the part is converting power.

CAPABILITY (0x19)

Bit [7]: Packet Error Checking

• 0 : Packet Error Checking not supported

Bit [6:5]: Maximum Bus Speed

• 01 : Maximum supported bus speed is 400 kHz

Bit [4]: SMBALERT#

• 1 : Enable the SMBus Alert Response protocol

Bit [3]: Numeric Format

• 0 : Numeric data is in LINEAR11, ULINEAR16, SLINEAR16

Bit [2]: AVSBus Support

• 0 : AVSBus not supported

Bit [1:0]: Reserved

SMBALERT_MASK (0x1B)

The SMBALERT_MASK command may be used to prevent a warning or fault condition from asserting the SMBALERT# signal. The bits in the mask byte align with the bits in the corresponding status register. For example if the STATUS_TEMPERATURE command code were sent with the mask byte 01000000b, then an Overtemperature Warning condition would be blocked from asserting SMBALERT#. This command cannot be used with STATUS_BYTE or STATUS_WORD. Since these commands are the logical or of underlying status registers, use the underlying status commands as the status command code sent to set a mask value. The access mode is a write word transaction for the write and a block write block read transaction for reading. Refer to the SMBus specification for details on this transaction.

VOUT_MODE (0x20)

The data byte for the VOUT_MODE command is one byte that consists of bit [7:5] as Mode and bit[4:0] as Exponent Parameter. The three-bit Mode sets whether the device uses the ULINEAR16, Half-precision IEEE 754 floating point, VID or DIRECT modes for output voltage related commands. The five-bit Parameter provides more information about the selected mode.

Bit [7]: Data type

• 1 : Device supports relative mode

Bit [6:5]: Data type

• 00 : Five bit two’s complement exponent for the mantissa delivered as the data bytes for an output voltage related command

Bit [4:0]: Exponent parameter

VOUT_COMMAND (0x21)

The VOUT_COMMAND command sets the output voltage in volts

Bit [15:0]: Two linear16 data bytes

Note that this part does not use VOUT_SCALE_LOOP. The value provided via the VOUT_COMMAND command is the voltage that the part will regulate the FB pin to. Any voltage divider used on that pin will need to be accounted for by the user when using VOUT_COMMAND.

VOUT_MAX (0x24)

The VOUT_MAX command sets the maximum output voltage. The purpose is to protect the devices on the output rail supplied by this device from a higher than acceptable output voltage

Bit [15:0]: Two linear 16 data bytes

VOUT_MARGIN_HIGH (0x25)

This VOUT_MARGIN_HIGH command loads the unit with the voltage to which the output is to be changed when the OPERATION command is set to “Margin High.”

Bit [15:0]: Two linear 16 data bytes

VOUT_MARGIN_LOW (0x26)

This VOUT_MARGIN_LOW command loads the unit with the voltage to which the output is to be changed when the OPERATION command is set to “Margin Low.”

Bit [15:0]: Two linear 16 data bytes

VOUT_TRANSITION_RATE (0x27)

VOUT_TRANSITION_RATE command sets the rate in mV/μs at which the output should change voltage.

Bits [15:11]: A 5 bit, two’s complement exponent for the calculation, fixed at -2

Bits [10:0]: An 11 bit, two’s complement mantissa for the calculation

Valid range: 0 to 31.75 V/ms

VIN_ON (0x35)

The VIN_ON command sets the value of the input voltage, in Volts, at which the unit should start power conversion.

Bits [15:11]: A 5 bit, two’s complement exponent, fixed at -1.

Bits [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0V to 15.5V

VOUT_OV_FAULT_LIMIT (0x40)

The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage measured at the sense or output pins that causes an output overvoltage fault.

Bit [15:0]: A 16 bit, two’s complement integer

VOUT_OV_FAULT_RESPONSE (0x41)

The VOUT_OV_FAULT_RESPONSE command instructs the device on what action to take in response to an output overvoltage fault

Valid values:

0x00: Continue without interruption

0x80: Shuts down and does not attempt to restart

0xC0: Shuts down and attempts to restart when the fault condition is no longer present

VOUT_OV_WARN_LIMIT (0x42)

The VOUT_OV_WARN_LIMIT command sets the value of the output voltage at the sense or output pins that causes an output voltage high warning. This value is typically less than the output overvoltage threshold.

Bit [15:0]: A 16 bit, two’s complement integer

VOUT_UV_FAULT_LIMIT (0x44)

The VOUT_UV_FAULT_LIMIT command sets the value of the output voltage at the sense or output pins that causes an output undervoltage fault. This fault is masked until the unit reaches the programmed output voltage. This fault is also masked when the unit is disabled.

Bit [15:0]: A 16 bit, two’s complement integer

VOUT_UV_FAULT_RESPONSE (0x45)

The VOUT_UV_FAULT_RESPONSE command instructs the device on what action to take in response to an output undervoltage fault

Valid values:

0x00: Continue without interruption

0x80: Shuts down and does not attempt to restart

IOUT_OC_FAULT_LIMIT (0x46)

The IOUT_OC_FAULT_LIMIT command sets the value of the output current, in Amperes, that causes the overcurrent detector to indicate an overcurrent fault condition

Bits [15:11]: A 5 bit, two’s complement exponent, fixed at -1

Bits [10:0]: An 11 bit, two’s complement mantissa

Valid range: 4.5 to 20 A

VIN_OV_FAULT_LIMIT (0x55)

The VIN_OV_FAULT_LIMIT command sets the value of the input voltage that causes an Input Overvoltage Fault.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at 0.

Bit [10:0]: An 11 bit, two’s complement mantissa

Maximum value: 18V

VIN_OV_FAULT_RESPONSE (0x56)

The VIN_OV_FAULT_RESPONSE command instructs the device on what action to take in response to an Input Overvoltage Fault.

Valid values:

0x00: Continue without interruption

0x80: Shuts down and does not attempt to restart

VIN_UV_WARN_LIMIT (0x58)

The VIN_UV_WARN_LIMIT command sets the value of the input voltage that causes an input voltage low warning. This value is typically greater than the Input Undervoltage Fault threshold, VIN_UV_FAULT_LIMIT

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -1

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0V to 15.5V

POWER_GOOD_ON (0x5E)

The POWER_GOOD_ON command sets the output voltage at which an optional POWER_GOOD signal should be asserted, indicating that the output voltage is valid. Note that depending on the choice of the device manufacturer that a device may drive a POWER_GOOD signal high or low to indicate that the signal is asserted.

Bit [15:0]: Two linear16 data bytes

TON_DELAY (0x60)

The TON_DELAY command sets the time, in milliseconds, from when a start condition is received until the output voltage starts to rise.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -1

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0 to 127.5ms

TON_RISE (0x61)

The TON_RISE command sets the time, in milliseconds, from when the output starts to rise until the voltage has entered the regulation band. A value of 0 milliseconds instructs the unit to bring its output voltage to the programmed regulation value as quickly as possible.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -2

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0 to 127.75ms

TON_MAX_FAULT_LIMIT (0x62)

The TON_MAX_FAULT_LIMIT command sets an upper limit, in milliseconds, on how long the unit can attempt to power up the output without reaching the output undervoltage fault limit. A value of 0 milliseconds means that there is no limit and that the unit can attempt to bring up the output voltage indefinitely.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -2

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0 to 127.75ms

TON_MAX_FAULT_RESPONSE (0x63)

The TON_MAX_FAULT_RESPONSE command instructs the device on what action to take in response to a TON_MAX fault.

Valid values:

0x00: Continue without interruption

0x80: Shuts down and does not attempt to restart

TOFF_DELAY (0x64)

The TOFF_DELAY command sets the time, in milliseconds, from when a stop condition is received (as programmed by the ON_OFF_CONFIG command) until the unit stops transferring energy to the output.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -1

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0 to 127.5ms

TOFF_FALL (0x65)

The TOFF_FALL command sets the time, in milliseconds, from the end of the turn-OFF delay time until the voltage is commanded to zero. A value of 0 milliseconds means that the device should ramp the output voltage down as fast as it can.

Bit [15:11]: A 5 bit, two’s complement exponent, fixed at -2

Bit [10:0]: An 11 bit, two’s complement mantissa

Valid range: 0 to 127.75ms

STATUS_WORD (0x79)

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 status registers. The low byte of the STATUS_WORD is the same register as the STATUS_BYTE command.

Bit [7]: An output voltage fault or warning has occurred

Bit [6]: An output current fault or warning has occurred.

Bit [5]: An input voltage fault or warning has occurred

Bit [4]: A manufacturer specific fault or warning has occurred

Bit [3]: The POWER_GOOD signal, if present, is negated

Bit [2]: A fan or airflow fault or warning has occurred (not used)

Bit [1]: A bit in STATUS_OTHER is set

Bit [0]: A fault type not given in bits [15:1] of the STATUS_WORD has been detected

STATUS_IOUT (0x7B)

The STATUS_IOUT command returns one byte of information relating to the status of the converter’s output current related faults.

Bit [7]: OUT_OC_FAULT

Bit [6]: IOUT_OC_LV_FAULT

Bit [5]: IOUT_OC_WARNING

Bit [4]: IOUT_UC_FAULT (not used)

Bit [3]: Current Share Fault (not used)

Bit [2]: In Power Limiting Mode (not used)

Bit [1]: POUT_OP_FAULT (not used)

Bit [0]: POUT_OP_WARNING (not used)

STATUS_INPUT (0x7C)

The STATUS_INPUT command returns one byte of information relating to the status of the input-related faults of the converter.

Bit [7]: VIN_OV_FAULT

Bit [6]: VIN_OV_WARNING

Bit [5]: VIN_UV_WARNING

Bit [4]: VIN_UV_FAULT

Bit [3]: Unit OFF For Insufficient Input Voltage

Bit [2]: IIN_OC_FAULT (not used)

Bit [1]: IIN_OC_WARNING (not used)

Bit [0]: PIN_OP_WARNING (not used)

STATUS_TEMPERATURE (0x7D)

The STATUS_TEMPERATURE command returns one byte of information relating to the status of the external temperature related faults.

Bit [7]: OT_FAULT

Bit [6]: OT_WARNING

Bit [5]: UT_WARNING (not used)

Bit [4]: UT_FAULT (not used)

Bit [3:0]: Reserved

STATUS_CML (0x7E)

The STATUS_CML command returns one byte of information relating to the status of the communication-related faults of the converter.

Bit [7]: Invalid or unsupported command received

Bit [6]: Invalid or unsupported data received

Bit [5]: Packet error check failed (not used)

Bit [4]: Memory fault detected

Bit [3]: Processor fault detected

Bit [2]: Reserved

Bit [1]: A communication fault other than the ones listed in this table has occurred

Bit [0]: Other memory or logic fault has occurred

READ_VOUT (0x8B)

The READ_VOUT command returns two bytes of data in the linear data format that represent the output voltage of the converter.

Bits [15:0]: A two’s complement mantissa for use with the exponent from VOUT_MODE, -8

READ_TEMPERATURE (0x8D)

The READ_TEMPERATURE command returns the external temperature in degrees Celsius.

Bits [15:11]: A two’s complement exponent, 0

Bits [10:0]: An 11 bit two’s complement mantissa

PMBUS_REVISION (0x98)

PMBUS_REVISION command stores or reads the revision of the PMBus to which the device is compliant.

Bit [7:4]: Indicate the revision of PMBus specification Part I to which the device is compliant

Bit [3:0]: Indicate the revision of PMBus specification Part II to which the device is compliant

MFR_MODEL (0x9A)

The MFR_MODEL command is used to either set or read the manufacturer’s model number. The actual data for this command is 1 byte. The high order byte here is the byte count in the SMBus block read and block write transactions.

MFR_REVISION (0x9B)

The MFR_REVISION command is used to either set or read the manufacturer’s revision number. The actual data for this command is 1 byte. The high order byte here is the byte count in the SMBus block read and block write transactions.

IC_DEVICE_ID (0xAD)

Th IC_DEVICE_ID command is a read-only block-read command that returns 2 bytes with the unique device-code identifier for the device. The actual data for this command is 1 byte. The high order byte here is the byte count in the SMBus block read and block write transactions.