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LTM4700
APPLICATIONS INFORMATION
Because of the adapter's limited current sourcing capabil-
ity, only the LTM4700s, their associated pull-up resistors
2
and the I
C pull-up resistors should be powered from the
ORed 3.3V supply. In addition any device sharing the I
bus connections with the LTM4700 should not have body
diodes between the SDA/SCL pins and their respective V
node because this will interfere with bus communication in
the absence of system power. If V
will not supply the power to the LTM4700s on the board. It
is recommended the RUNn pins be held low or no voltage
configuration resistors inserted to avoid providing power
to the load until the part is fully configured.
The LTM4700 is fully isolated from the host PC's ground by
the DC1613A.The 3.3V from the adapter and the LTM4700
V
pin must be driven to each LTM4700 with a separate
DD33
PFET. If both V
and EXTV
IN
pins can be in parallel because the on-chip LDO is off. The
controller 3.3V current limit is 100mA but typical V
currents are under 15mA. The V
INTV
/EXTV
pin. Normally this is not an issue if V
CC
CC
is open.
LTpowerPlay: AN INTERACTIVE GUI FOR DIGITAL
POWER
LTpowerPlay (Figure 31) is a powerful Windows-based
development environment that supports Analog De-
vices digital power system management ICs including
the LTM4700. The software supports a variety of differ-
ent tasks. LTpowerPlay can be used to evaluate Analog
Devices ICs by connecting to a demo board or the user
application. LTpowerPlay can also be used in an offline
mode (with no hardware present) in order to build multiple
IC configuration files that can be saved and reloaded at a
later time. LTpowerPlay provides unprecedented diagnostic
and debug features. It becomes a valuable diagnostic tool
during board bring-up to program or tweak the power
system or to diagnose power issues when bring up rails.
LTpowerPlay utilizes Analog Devices' USB-to-I
PMBus adapter to communication with one of the many
potential targets including the DC2165A demo board, the
DC2298A socketed programming board, or a customer
60
is applied, the DC1613A
IN
are not applied, the V
CC
DD33
DD33
does back drive the
DD33
2
C/SMBus/
For more information
target system. The software also provides an automatic
update feature to keep the revisions current with the latest
set of device drivers and documentation.
2
C
A great deal of context sensitive help is available with
LTpowerPlay along with several tutorial demos. Complete
DD
information is available at:
ltpowerplay.com
PMBus COMMUNICATION AND COMMAND
PROCESSING
The LTM4700 has a one deep buffer to hold the last data
written for each supported command prior to processing
as shown in Figure 32, Write Command Data Processing.
When the part receives a new command from the bus, it cop-
ies the data into the Write Command Data Buffer, indicates
to the internal processor that this command data needs
to be fetched, and converts the command to its internal
format so that it can be executed. Two distinct parallel blocks
manage command buffering and command processing
IN
(fetch, convert, and execute) to ensure the last data written
to any command is never lost. Command data buffering
handles incoming PMBus writes by storing the command
data to the Write Command Data Buffer and marking these
commands for future processing. The internal processor
runs in parallel and handles the sometimes slower task of
fetching, converting and executing commands marked for
processing. Some computationally intensive commands
(e.g., timing parameters, temperatures, voltages and
currents) have internal processor execution times that
may be long relative to PMBus timing. If the part is busy
processing a command, and new command(s) arrive,
execution may be delayed or processed in a different order
than received. The part indicates when internal calculations
are in process via bit 5 of MFR_COMMON ("calculations
not pending"). When the part is busy calculating, bit 5 is
cleared. When this bit is set, the part is ready for another
command. An example polling loop is provided in Figure
34 which ensures that commands are processed in order
while simplifying error handling routines.
When the part receives a new command while it is busy,
it will communicate this condition using standard PMBus
www.analog.com
Rev. B
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