LTC2977 datasheet(68/138 Pages) AD

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LTM4664A

Rev. 0

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UNDERVOLTAGE LOCKOUT

The LTM4664A PSM is initialized by an internal thresh-

old-based UVLO where VINS3 must be approximately 4V

and INTVCC, VDD33, and VDD25 must be within approxi-

mately 20% of their regulated values. In addition, VDD33

must be within approximately 7% of the targeted value

before the RUN_Cn pin is released. After the part has

initialized, an additional comparator monitors VINS3. The

VIN_ON threshold must be exceeded before the power

sequencing can begin. When VINS3 drops below the VIN_

OFF threshold, the SHARE_CLK pin will be pulled low and

VINS3 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

FAULTB is held low when VINS3 is applied, ALERT will be

asserted low even if the part is programmed to not assert

ALERT when FAULTB is held low. If I2C communication

occurs before the LTM4664A 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,

ALERT is asserted low.

It is possible to program the contents of the NVM in

the application if the VDD33 supply is externally driven

directly to VDD33 or through EXTVCC. This will activate the

digital portion of the LTM4664A PSM without engaging

the high voltage sections. PMBus communications are

valid in this supply configuration. If VINS3 has not been

applied to the LTM4664A PSM, 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 issue the following set of com-

mands: 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 a 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 LTM4664A FAULT_Cn pins are configurable to indicate

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

and peak over current faults. In addition, the FAULT_Cn

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

Refer to the PMBus section of the 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 LTM4664A PSM. The fault

logging 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 LTM4664A PSM internal temperature is in excess

of 85°C, writes into the NVM (other than fault logging)

are not recommended. 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 LTM4664A PSM has the following open-drain pins:

3.3V Pins

1. FAULT_Cn

2. SYNC

3. SHARE_CLK

4. PGOOD_Cn

5V Pins (5V pins operate correctly when pulled to 3.3V.)

1. RUN_Cn

2. ALERT

3. SCL

4. SDA

DUAL 25A/30A PSM APPLICATIONS INFORMATION

LTC2977 Datasheet(PDF) 68 Page - Analog Devices

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