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APPLICATIONS INFORMATION
UNDERVOLTAGE LOCKOUT
The LTM4700 is initialized by an internal threshold-based
UVLO where VIN must be approximately 4V and INTVCC,
VDD33, and VDD25 must be within approximately 20% of
their regulated values. In addition, VDD33 must be within
approximately 7% of the targeted value before the RUN
pin is released. After the part has initialized, an additional
comparator monitors VIN. The VIN_ON threshold must be
exceeded before the power sequencing can begin. When
VIN drops below the VIN_OFF threshold, the SHARE_CLK
pin will be pulled low and 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 FAULTB is held low when VIN 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 LTM4700 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. This will activate the digital portion of
the LTM4700 without engaging the high voltage sections.
PMBus communications are valid in this supply configu-
ration. If VIN has not been applied to the LTM4700, 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 fol-
lowing 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 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 LTM4700 FAULT 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 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
n
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.
The OV response is automatic. If an OV condition is de-
tected, TGn goes low and BGn is asserted.
Fault logging is available on the LTM4700. 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 LTM4700 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 LTM4700 has the following open-drain pins:
3.3V Pins
1. FAULTn
2. SYNC
3. SHARE_CLK
4. PGOODn
5V Pins (5V pins operate correctly when pulled to 3.3V.)
1. RUNn
2. ALERT
3. SCL
4. SDA
For more information
www.analog.com
LTM4700
Rev. B
55
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