LTM4677 datasheet(27/116 Pages) AD

27 / 116 page

LTC3883/LTC3883-1

Rev. F

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OPERATION

Device addressing provides the standard means of the

PMBus master communicating with a single instance

of an LTC3883. The value of the device address is set

by a combination of the ASEL configuration pin and the

MFR_ADDRESS command. Device addressing can be

disabled by writing a value of 0x80 to the MFR_ADDRESS.

Rail addressing provides a means of the PMBus master

addressing a set of LTC3883s connected to the same

output rail, simultaneously. This is similar to global ad-

dressing,however,thePMBusaddresscanbedynamically

assigned by using the MFR_RAIL_ADDRESS command.

It is recommended that rail addressing should be limited

to command write operations.

All four means of PMBus addressing require the user to

employdisciplinedplanningtoavoidaddressingconflicts.

RESPONSES TO VOUT AND IOUT FAULTS

VOUTOVandUVconditionsaremonitoredbycomparators.

The OV and UV limits are set in three ways.

As a Percentage of the VOUT if Using the Resistor Con-

figuration 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 80ms. The IOUT calculation accounts for the sense

resistor and the temperature coefficient of the resistor. The

input channel current is equal to the sum of output current

times the PWM duty cycle plus the input offset current

for each channel. If this calculated input current exceed

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 LTC3883 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 until the

overvoltage condition is cleared regardless of the PMBus

VOUT_OV_FAULT_RESPONSEcommandbytevalue.This

hardware level fault response delay is typically 2µs from

the overvoltage 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

ShutDownImmediately—RetryIndefinitelyattheTime

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 5.

Output Undervoltage Response

The response to an undervoltage comparator output can

be either:

Ignore

Shut Down Immediately—Latch Off

ShutDownImmediately—RetryIndefinitelyattheTime

Interval Specified in MFR_RETRY_DELAY

The UV responses can be deglitched. See Table 6.

Peak Output Overcurrent Fault Response

Due to the current mode control algorithm, peak output

current across the inductor is always limited on a cycle by

cycle basis. The value of the peak current limit is specified

in sense voltage in the EC table. The current limit circuit

operatesbylimitingtheITHmaximumvoltage.IfDCRsens-

ing is used, the ITH maximum voltage has a temperature

dependency directly proportional to the TC of the DCR

of the inductor. The LTC3883 automatically monitors the

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