Undervoltage Lockout; Fault Detection And Handling; Open-Drain Pins - Analog Devices Linear ADI Power LTM4681 Manual

APPLICATIONS INFORMATION

UNDERVOLTAGE LOCKOUT

The LTM4681 is initialized by an internal threshold-based
UVLO where V must be approximately 4V and INTV
IN
, V , and V
nn DD33_nn DD25_nn
20% of their regulated values. In addition, V
be within approximately 7% of the targeted value before
the RUNn pin is released. After the part has initialized, an
additional comparator monitors V
old must be exceeded before the power sequencing can
begin. When V drops below the VIN_OFF threshold,
IN
the SHARE_CLK_nn pin will be pulled low and V
increase above the VIN_ON threshold before the con-
troller will restart. The normal start-up sequence will be
allowed after the VIN_ON threshold is crossed. If FAULTn
is held low when V is applied, ALERTnn will be asserted
IN
low even if the part is programmed to not assert ALERTnn
when FAULTn is held low. If I
before the LTM4681 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 V
DD33_nn
directly to V or through V
DD33_nn
digital portion of the LTM4681 without engaging the high
voltage sections. PMBus communications are valid in this
supply configuration. If V
LTM4681, 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 commands: 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
V is applied a MFR_RESET command must be issued to
IN
allow the PWM to be enabled and valid ADC conversions
to be read.

FAULT DETECTION AND HANDLING

The LTM4681 FAULTn pins are configurable to indicate
a variety of faults including OV, UV, OC, OT, timing faults,
and peak over current faults. In addition, the FAULTn pins
must be within approximately
DD33_nn
. The VIN_ON thresh-
IN
IN
2
C communication occurs
supply is externally driven
. This will activate the
BIAS
has not been applied to the
IN
For more information
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:
CC_
Ignore
n
must
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
Time Interval Specified in MFR_RETRY_DELAY
Refer to the PMBus section of the data sheet and the
PMBus specification for more details.
must
The OV response is automatic. If an OV condition is
detected, TGn goes low and BGn is asserted.
Fault logging is available on the LTM4681. 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 LTM4681 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 LTM4681 has the following open-drain pins:
3.3V Pins
1. FAULTn
2. SYNC_nn
3. SHARE_CLK_nn
4. PGOODn
5V Pins (5V pins operate correctly when pulled to 3.3V.)
1. RUNn
2. ALERT_nn
3. SCL_nn
4. SDA_nn
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LTM4681
Rev. A
61