LTM4682 datasheet(60/130 Pages) AD

60 / 130 page

LTM4682

Rev. 0

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APPLICATIONS INFORMATION

not pull a negative current, and the output will be pulled

low by the load, not the power stage. The maximum fall

time is limited to 1.3 seconds. The shorter the TOFF_FALL

time is set, the larger the discrete steps in the TOFF_FALL

ramp will appear. The number of steps in the ramp is equal

to TOFF_FALL/0.1ms.

UNDERVOLTAGE LOCKOUT

The LTM4682 is initialized by an internal threshold-based

UVLO where VIN must be approximately 4V and INTVCC_nn,

VDD33_nn, and VDD25_nn must be within approximately

20% of their regulated values. In addition, VDD33_nn must

be within approximately 7% of the targeted value before

the RUNn pin is released. After the part has initialized, an

additional comparator monitors VIN. The VIN_ON thresh-

old must be exceeded before the power sequencing can

begin. When the VIN drops below the VIN_OFF thresh-

old, the SHARE_CLK_nn pin will be pulled low, and the

VIN must increase above the VIN_ON threshold before

the controller will restart. The normal start-up sequence

will be allowed after the VIN_ON threshold is crossed. If

FAULTn is held low when VIN is applied, ALERTnn will be

asserted low even if the part is programmed not to assert

ALERTnn when FAULTn is held low. If I2C communica-

tion occurs before the LTM4682 is out of reset and only

a portion of the command is seen by the part, this can

be interpreted as a CML fault. If a CML fault is detected,

ALERTnn is asserted low.

It is possible to program the contents of the NVM in the

application if the VDD33_nn supply is externally driven directly

to VDD33_nn or through VBIAS. This will activate the digital

portion of the LTM4682 without engaging the high-voltage

sections. PMBus communications are valid in this supply

configuration. If the VIN hasnotbeenappliedtotheLTM4682,

bit 3 (NVM Not Initialized) in MFR_COMMON will be asserted

low. If this condition is detected, the part will only respond to

addresses 5A and 5B. To initialize the part, the following set

of commands are used: global address 0x5B command 0xBD

data 0x2B followed by global address 5B command 0xBD and

data 0xC4. The part will now respond to the correct address.

Configure the part as desired, then issue a STORE_USER_

ALL. When VIN is applied, an MFR_RESET command must

be issued to allow the PWM to be enabled and valid ADC

conversions to be read.

FAULT DETECTION AND HANDLING

The LTM4682 FAULTn pins are configurable to indicate a

variety of faults including, OV, UV, OC, OT, timing faults,

and peak overcurrent faults. In addition, the FAULTn pins

can be pulled low by external sources, indicating a fault

in some other portion of the system. The fault response

is configurable and allows the following options:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the Time

Interval Specified in MFR_RETRY_DELAY

See the PMBus PMBus Command Details, and the PMBus

Command Summary sections of this data sheet and the

PMBus specification for more details.

The OV response is automatic. If an OV condition is

detected, TGn goes low, and BGn is asserted.

Fault logging is available on the LTM4682. The fault log-

ging is configurable to automatically store data when a

fault occurs that causes the unit to fault off. The header

portion of the fault logging table contains peak values. It

is possible to read these values at any time. This data will

be useful while troubleshooting the fault.

If the LTM4682 internal temperature is in excess of 85°C,

writes into the NVM (other than fault logging) is not rec-

ommended. The data will still be held in RAM, unless

the 3.3V supply UVLO threshold is reached. If the die

temperature exceeds 130°C, all NVM communication is

disabled until the die temperature drops below 120°C.

OPEN-DRAIN PINS

The LTM4682 has the following open-drain pins:

3.3V Pins

1. FAULTn

2. SYNC_nn

LTM4682 Datasheet(PDF) 60 Page - Analog Devices

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