Datasheet

MAX34451 PMBus 16-Channel V/I Monitor and
12-Channel Sequencer/Marginer
www.maximintegrated.com
Maxim Integrated │ 24
Power-On Sequencing
The activation of all power-supply channels (even across
multiple devices) is initiated from a common START
signalthatcaneitherbetheCONTROL0orCONTROL1
pin, or the OPERATION command. Each power-supply
channel on the device can be sequenced on by one of the
followingmethods:
● Powerisappliedtothedevice.
● TheCONTROL0pingoesactive.
● TheCONTROL1pingoesactive.
● TheOPERATIONcommandisreceived.
● ThelogiccombinationofpowergoodsandGPIisvalid.
● TheSEQ pin signal is matched.
Each enabled PSENn output goes active (either active
highoractivelow,asdefinedinMFR_PSEN_CONFIG)
after the associated delay time programmed in TON_
DELAY.Thepowersuppliescanbesequencedoninany
order. Each channel can be sequenced on with either
time-based or event-based conditions. The output volt-
age of each power supply is monitored to ensure that the
supply crosses the power-good-on level (as configured
inthePOWER_GOOD_ONcommand)withinaprogram-
mabletimelimit,asconfiguredintheTON_MAX_FAULT_
LIMITcommand.Thispower-uptimelimitcanbedisabled
by configuring TON_MAX_FAULT_LIMIT to 0000h. For
channelsusingevent-basedsequencing,theMFR_TON_
SEQ_MAXcommanddeterminesthemaximumtimelimit
forthesequence-oneventtooccur.LiketheTON_MAX_
FAULT_LIMIT, this limit can be disabled by configuring
MFR_TON_SEQ_MAXto0000h.Thereisaone-to-one
correspondencebetweentheRSninputsandthePSENn
outputs. For example, RS6 monitors the power supply
controlledbyPSEN6.Allpower-onsequencingisgated
by detected faults. Before any power-supply channel is
enabled (or the FAULTn output deasserted) the device
checks for overvoltage, overcurrent, and temperature
faults that are enabled (but not for undervoltage since the
supplyisoff).
Power-Off Sequencing
The order in which the supplies are disabled is deter-
minedwiththeTOFF_DELAYconfiguration.Alternatively,
all the power supplies can be switched off immediately,
asconfiguredintheON_OFF_CONFIGcommandorwith
theOPERATIONcommand.
As configured with the ON_OFF_CONFIG command,
either the CONTROL0 or CONTROL1 pin or the
OPERATION command is the master off switch. When
eithertheCONTROL0orCONTROL1pingoesinactive,
ortheOPERATIONoffcommandisreceived(oroneof
the enabled FAULTnpinsasserted),thepowersupplies
aresequencedoff.Neitherthepower-good(PG)orGPI
logic combinations, nor the SEQ pin, can be used to turn
off the power supplies.
Sequencing Example
As an example, Figure 3 details a simple sequenc-
ing scheme consisting of four power supplies using a
mixture of time-based and event-based sequencing.
Channels 0 and 2 use time-based sequencing and
channels 1 and 5 use event-based sequencing. When
either the CONTROL0 or CONTROL1 pin goes active,
ortheOPERATIONcommandisreceived(asdefinedby
the ON_OFF_CONFIG command), PSEN0 is asserted
after the delay time configured inTON_DELAY. RS0 is
monitoredtoensurethatthePSEN0supplycrossesthe
power-good-onlevel(asconfiguredinPOWER_GOOD_
ON) within a programmabletime limit (as configuredin
TON_MAX_FAULT_LIMIT).PSEN2operatesinasimilar
fashionasPSEN0,butwithadifferentTON_DELAYanda
differentTON_MAX_FAULT_LIMIT.Sincethepower-upof
channels0and2arebasedsolelyontheirTON_DELAY
values, these channels are time-based.
When RS2 crosses its power-good-on level, PSEN5 is
asserted after its configuredTON_DELAYand similarly,
PSEN1 asserts when RS5 crosses its power-good-on
level.Sincethepower-upofchannels5and1arebased
on the power-good states of other channels, these
channels are event-based. The MFR_TON_SEQ_MAX
command can be used to ensure that these events occur
and the power-up sequence does not hang waiting for an
eventtotranspire.WhenRS1crossesitspower-good-on
level, it has been configured to generate a SEQ pin signal
to communicate to another device to turn on one or more
of its power supplies.
Table 8. OPERATION Command Sequence Control Options
GROUP
OPERATION COMMAND (PAGE = 255)
ON SOFT-OFF IMMEDIATE OFF
SEQUENCE0
80hor81h 40hor41h 00hor01h
SEQUENCE1 80hor82h 40hor42h 00hor02h