37
Rev. B
OPERATION
Global addressing provides a means of the PMBus master
to address all LTM4680 devices on the bus. The LTM4680
global address is fixed 0x5A (7-bit) or 0xB4 (8-bit) and
cannot be disabled. Commands sent to the global address
act the same as if PAGE is set to a value of 0xFF. Commands
sent are written to both channels simultaneously. Global
command 0x5B (7-bit) or 0xB6 (8-bit) is paged and allows
channel specific command of all LTM4680 devices on the
bus. Other ADI device types may respond at one or both
of these global addresses. Reading from global addresses
is strongly discouraged.
Device addressing provides the standard means of the
PMBus master communicating with a single instance
of an LTM4680. The value of the device address is set
by a combination of the ASEL configuration pin and the
MFR_ ADDRESS command. When this addressing means
is used, the PAGE command determines the channel being
acted upon. Device addressing can be disabled by writing
a value of 0x80 to the MFR_ADDRESS.
Rail addressing provides a means for the bus master to
simultaneously communicate with all channels connected
together to produce a single output voltage (PolyPhase).
While similar to global addressing, the rail address can
be dynamically assigned with the paged MFR_RAIL_
ADDRESS command, allowing for any logical grouping
of channels that might be required for reliable system
control. Reading from rail addresses is also strongly
discouraged.
All four means of PMBus addressing require the user to
employ disciplined planning to avoid addressing conflicts.
Communication to LTM4680 devices at global and rail
addresses should be limited to command write operations.
RESPONSES TO V
OUT
AND I
IN
/I
OUT
FAULTS
V
OUT
OV and UV conditions are monitored by compara-
tors. The OV and UV limits are set in three ways:
n
As a Percentage of the V
OUT
if Using the Resistor
Configuration Pins
n
In NVM if Either Programmed at the Factory or
Through the GUI
n
By PMBus Command
The I
IN
and I
OUT
overcurrent monitors are performed by
ADC readings and calculations. Thus these values are
based on average currents and can have a time latency
of up to t
CONVERT
. The I
OUT
calculation accounts for the
DCR and their temperature coefficient. The input current is
equal to the voltage measured across the R
SENSE
resistor
divided by the resistors value as set with the MFR_RVIN
command. If this calculated input current exceeds the
IN_OC_WARN_LIMIT the
ALERT
pin is pulled low and
the IIN_OC_WARN bit is asserted in the STATUS_INPUT
command.
The digital processor within the LTM4680 provides the
ability to ignore the fault, shut down and latch off or shut
down and retry indefinitely (hiccup). The retry interval
is set in MFR_RETRY_ DELAY and can be from 120ms
to 83.88 seconds in 1ms increments. The shutdown for
OV/UV and OC can be done immediately or after a user
selectable deglitch time.
Output Overvoltage Fault Response
A programmable overvoltage comparator (OV) guards
against transient overshoots as well as long-term over-
voltages at the output. In such cases, the top MOSFET
is turned off and the bottom MOSFET is turned on.
However, the reverse output current is monitored while
device is in OV fault. When it reaches the limit, both top
and bottom MOSFETs are turned off. The top and bot-
tom MOSFETs will keep their state until the overvoltage
condition is cleared regardless of the PMBus VOUT_OV_
FAULT_RESPONSE command byte value. This hardware
level fault response delay is typically 2µs from the over-
voltage condition to BG asserted high. Using the VOUT_
OV_FAULT_RESPONSE command, the user can select
any of the following behaviors:
n
OV Pull-Down Only (OV Cannot Be Ignored)
n
Shut Down (Stop Switching) Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
Time Interval Specified in MFR_RETRY_DELAY
Either the Latch Off or Retry fault responses can be de-
glitched in increments of (0-7) • 10µs. See Table 15.