AN 896: Multi-Rail Power Sequencer and Monitor Reference Design

ID 683778
Date 9/30/2019
Public
Document Table of Contents

4.1. PMBus* Commands Implementation

The design implements different register control and status commands, depending on the functionality level you select in the Sequencer Voltage Monitor component. The commands can address one or two bytes of data. The design stores all data for the output voltage and related parameters in the DIRECT format.
Table 9.   Power Sequencer PMBus* Commands DescriptionThis table lists the supported PMBus* commands. The design implements commands marked with * only if you select the Full-featured option for the Functionality Level parameter of the Sequencer Voltage Monitor component.
Command Code (Address) Bit Name SMBus Transaction Description
0x00 [7:0] PAGE

Read Byte

Write Byte

Selects the page of commands for the voltage rail being accessed.

Range of valid page values is 0x00 to 0x8F (143) and relates to each VOUT rail.

0x03   CLEAR_FAULTS

Send Byte

Clears all warnings and faults in the write-to-clear status bits.

0x35 [15:0] VIN_ON 1 *

Read Word

Write Word

Sets the value of the input voltage at which it is sufficiently high for the design to begin sequencing the output rails on.
0x36 [15:0] VIN_OFF 1 *

Read Word

Write Word

Sets the value of the input voltage at which it has dropped low enough that the design must sequence the output rails off.
0x40 [15:0] VOUT_OV_FAULT_LIMIT 1 *

Read Word

Write Word

Sets the value of the output voltage that causes an output overvoltage fault.
0x41 VOUT_OV_FAULT_RESP

Read Byte

Write Byte

Instructs the device on the action to take when there is an output overvoltage fault.
[7:6] Response

  • 00—Continue operation without interruption
  • 01—Invalid
  • 10—Sequence a power down in reverse order and respond according to the retry setting in bits [5:3]
  • 11—Invalid
[5:3] Retry Setting 2

Indicates the number of times the device attempts to restart from a fault.

  • 0—Do not attempt a restart and remain disabled until the fault clears and ENABLE input toggles
  • 1 to 6—Retry for the specified number of attempts, then stop and remain disabled until the fault clears and the ENABLE input toggles
  • 7—Retry infinitely
[2:0] Delay Time 3

Specifies the delay interval between attempts to restart.

  • 0—No delay
  • 1 to 7—Use the Delay Time Between Restarts parameter setting in the Power Sequencer component
0x42 [15:0] VOUT_OV_WARN_LIMIT 1 *

Read Word

Write Word

Sets the value of the output voltage that causes an output overvoltage warning.
0x43 [15:0] VOUT_UV_WARN_LIMIT 1 *

Read Word

Write Word

Sets the value of the output voltage that causes an output undervoltage warning.
0x44 [15:0] VOUT_UV_FAULT_LIMIT 1 *

Read Word

Write Word

Sets the value of the output voltage that causes an output undervoltage fault.
0x45 VOUT_UV_FAULT_RESP

Read Byte

Write Byte

Instructs the device on the action to take when there is an output undervoltage fault.
[7:6] Response

  • 00—Continue operation without interruption
  • 01—Invalid
  • 10—Sequence a power down in reverse order and respond according to the retry setting in bits [5:3]
  • 11—Invalid
[5:3] Retry Setting2

Indicates the number of times the device attempts to restart from a fault.

  • 0—Do not attempt a restart and remain disabled until the fault clears and ENABLE input toggles
  • 1 to 6—Retry for the specified number of attempts, then stop and remain disabled until the fault clears and the ENABLE input toggles
  • 7—Retry infinitely
[2:0] Delay Time3

Specifies the delay interval between attempts to restart.

  • 0—No delay
  • 1 to 7—Use the Delay Time Between Restarts parameter setting in the Power Sequencer component
0x55 [15:0] VIN_OV_FAULT_LIMIT 1 *

Read Word

Write Word

Sets the value of the input voltage that causes an input overvoltage fault.
0x56 VIN_OV_FAULT_RESP

Read Byte

Write Byte

Instructs the device on the action to take when there is an input overvoltage fault.
[7:6] Response

  • 00—Continue operation without interruption
  • 01—Invalid
  • 10—Sequence a power down in reverse order and respond according to the retry setting in bits [5:3]
  • 11—Invalid
[5:3] Retry Setting 2

Indicates the number of times the device attempts to restart from a fault.

  • 0—Do not attempt a restart and remain disabled until the fault clears and ENABLE input toggles
  • 1 to 6—Retry for the specified number of attempts, then stop and remain disabled until the fault clears and the ENABLE input toggles
  • 7—Retry infinitely
[2:0] Delay Time 3

Specifies the delay interval between attempts to restart.

  • 0—No delay
  • 1 to 7—Use the Delay Time Between Restarts parameter setting in the Power Sequencer component
0x57 [15:0] VIN_OV_WARN_LIMIT 1 *

Read Word

Write Word

Sets the value of the input voltage that causes an input overvoltage warning.
0x58 [15:0] VIN_UV_WARN_LIMIT 1 *

Read Word

Write Word

Sets the value of the input voltage that causes an input undervoltage warning.
0x59 [15:0] VIN_UV_FAULT_LIMIT 1 *

Read Word

Write Word

Sets the value of the input voltage that causes an input undervoltage fault.
0x5A VIN_UV_FAULT_RESP

Read Byte

Write Byte

Instructs the device on the action to take when there is an input undervoltage fault.
[7:6] Response

  • 00—Continue operation without interruption
  • 01—Invalid
  • 10—Sequence a power down in reverse order and respond according to the retry setting in bits [5:3]
  • 11—Invalid
[5:3] Retry Setting 2

Indicates the number of times the device attempts to restart from a fault.

  • 0—Do not attempt a restart and remain disabled until the fault clears and ENABLE input toggles
  • 1 to 6—Retry for the specified number of attempts, then stop and remain disabled until the fault clears and the ENABLE input toggles
  • 7—Retry infinitely
[2:0] Delay Time 3

Specifies the delay interval between attempts to restart.

  • 0—No delay
  • 1 to 7—Use the Delay Time Between Restarts parameter setting in the Power Sequencer component
0x5E [15:0] POWER_GOOD_ON 1 *

Read Word

Write Word

Sets the value of the output voltage at which it is sufficiently high for the design to assert the POWER_GOOD signal to the Power Sequencer component, indicating that the output voltage is valid.
0x5F [15:0] POWER_GOOD_OFF 1 *

Read Word

Write Word

Sets the value of the output voltage at which it has dropped low enough for the design to deassert the POWER_GOOD signal to the Power Sequencer component, indicating that the output voltage is not valid.
0x78 [7:0] STATUS_BYTE
  • [7]: BUSY
  • [6]: OFF
  • [5]: VOUT_OV_FAULT
  • [4]: Reserved
  • [3]: VIN_UV_FAULT
  • [2]: Reserved
  • [1]: CML
  • [0]: NONE_OF_THE_ABOVE

Read Byte

A value of 1 for any bit indicates that a fault or warning has occurred in the associated status registers.
0x79 [15:0] STATUS_WORD
  • [15]: VOUT
  • [14]: Reserved
  • [13]: INPUT
  • [12]: MFRSPECIFIC
  • [11]: PG_STATUS#
  • [10]: Reserved
  • [9]: OTHER
  • [8]: UNKNOWN
  • [7]: BUSY
  • [6]: OFF
  • [5]: VOUT_OV_FAULT
  • [4]: Reserved
  • [3]: VIN_UV_FAULT
  • [2]: Reserved
  • [1]: CML
  • [0]: NONE_OF_THE_ABOVE

Read Word

A value of 1 for any bit indicates that a fault or warning has occurred in the associated status registers.

Bits [7:0] are duplicate of STATUS_BYTE.

0x7A [7:0] STATUS_VOUT
  • [7]: VOUT_OV_FAULT
  • [6]: VOUT_OV_Warning
  • [5]: VOUT_UV_Warning
  • [4]: VOUT_UV_FAULT
  • [3]: Reserved
  • [2]: Reserved
  • [1]: Reserved
  • [0]: Reserved

Read Byte

Write Byte

A value of 1 for any bit indicates that a fault or warning has occurred and flagged for the various conditions.

To clear the flag, write 1 to the particular bit in the register.

0x7C [7:0] STATUS_INPUT
  • [7]: VIN_OV_FAULT
  • [6]: VIN_OV_Warning
  • [5]: VIN_UV_Warning
  • [4]: VIN_UV_FAULT
  • [3]: Unit Off for Low VIN
  • [2]: Reserved
  • [1]: Reserved
  • [0]: Reserved

Read Byte

Write Byte

A value of 1 for any bit indicates that a fault or warning has occurred and flagged for the various conditions.

To clear the flag, write 1 to the particular bit in the register.

0x7E [7:0] STATUS_CML
  • [7]: Invalid/Unsupported Command
  • [6]: Invalid/Unsupported Data
  • [5]: Reserved
  • [4]: Reserved
  • [3]: Reserved
  • [2]: Reserved
  • [1]: Reserved
  • [0]: Reserved

Read Byte

Write Byte

A value of 1 for any bit indicates that a fault or warning has occurred and flagged for the various conditions.

To clear the flag, write 1 to the particular bit in the register.

0x7F [7:0] STATUS_OTHER
  • [7]: Reserved
  • [6]: Reserved
  • [5]: Reserved
  • [4]: Reserved
  • [3]: Reserved
  • [2]: Reserved
  • [1]: Reserved
  • [0]: First to Assert SMBALERT#

Read Byte

Write Byte

A value of 1 for any bit indicates that a fault or warning has occurred and flagged for the various conditions.

To clear the flag, write 1 to the particular bit in the register.

0x88 [15:0] READ_VIN 1

Read Word

Indicates the present input voltage level.
0x8B [15:0] READ_VOUT 1

Read Word

Indicates the present output voltage level.
1 The levels are specified in the PMBus* DIRECT format. For information about translating to and from the DIRECT format, refer to the related information.
2 The Retry Setting value is common across all pages, and warnings or faults. The controller attempts to recover after a fault until it reaches the global number of times to retry. The retry counter resets whenever the ENABLE input toggles low. The Response setting for this same command is unique to each warning or fault.
3 The Delay Time setting is common across all pages, and warnings or faults. After all power good signals deasserts, the controller waits between retry attempts for the specified time before power sequencing the rails back up. The Response setting for this same command is unique to each warning or fault.

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