LTM4664 datasheet(49/138 Pages) AD

49 / 138 page

LTM4664A

Rev. 0

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Global addressing provides a means of the PMBus master

to address all LTM4664A PSM devices on the bus. The

LTM4664A PSM 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 chan-

nels simultaneously. Global command 0x5B (7-bit) or

0xB6 (8-bit) is paged and allows channel specific com-

mand of all LTM4664A PSM devices on the bus. Other LTC

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 LTM4664A PSM. 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 LTM4664A PSM devices at global and rail

addresses should be limited to command write operations.

RESPONSES TO VOUT AND IIN/IOUT FAULTS

VOUT OV and UV conditions are monitored by compara-

tors. The OV and UV limits are set in three ways:

As a Percentage of the VOUT if Using the Resistor

Configuration Pins

In NVM if Either Programmed at the Factory or Through

the GUI

By PMBus Command

The IIN and IOUT 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 tCONVERT. The IOUT calculation accounts for the

DCR and their temperature coefficient. The input cur-

rent is equal to the voltage measured across the RSENSE

resistor divided by the resistors value as set with the

MFR_IIN_CAL_GAIN 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 LTM4664A PSM provides

the ability to ignore the fault, shut down and latch off or

shut down and retry indefinitely (hiccup). The retry inter-

val 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:

OV Pull-Down Only (OV Cannot Be Ignored)

Shut Down (Stop Switching) Immediately—Latch Off

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 14.

DUAL 25A/30A PSM OPERATION

LTM4664 Datasheet(PDF) 49 Page - Analog Devices

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