LTC3882_15 Datasheet, PDF (23/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
OPERATION
The output overvoltage comparator guards against transient
overshoots as well as long term overvoltages at the output.
When an output OV fault is detected the top MOSFET for
that channel is commanded off and the bottom MOSFET is
commanded on until the overvoltage condition is cleared
or for most PWM control protocols reverse overcurrent
is detected. See I_OUT faults below.
UV faults and warnings are masked if the channel has
been commanded off or until all of the following criteria
are achieved.
• TON_DELAY Has Expired
• TON_RISE Ramp Has Completed
If programmed to operate in CCM, the LTC3882 also uses
the negative of IOUT_OC_FAULT_LIMIT to detect a reverse
overcurrent (ROC) fault. When an ROC fault occurs the
controller immediately disables both top and bottom FETs,
unless the EN pin for that channel is tied high with three-
state PWM output protocol selected.
OC and ROC faults are both handled according to the
IOUT_OC_FAULT_RESPONSE for that channel. Either
hardware response can result in current-limited operation
using pulse truncation or skipping. Because the LTC3882
uses leading edge modulation, this will cause a shift in
average phase toward 0° on the faulted channel and an
increase in input ripple current
• TON_MAX_FAULT_LIMIT Has Been Reached
• IOUT_OC_FAULT_LIMIT Has Not Been Reached
• TOFF_FALL Is Not in Progress
Output OC warnings are determined from multiplexed
monitor ADC conversions. The LTC3882 has no hardwired
PWM response if an output OC warning occurs.
Output UV warnings are determined from multiplexed
monitor ADC conversions. The LTC3882 has no hardwired
PWM response for output UV faults or warnings.
Power Good Indication
An LTC3882 master phase indicates Power Good in STA-
TUS_WORD based on programmed UV and OV fault limits.
Power Good is indicated as long as the phase is enabled
to run and V_OUT is between the UV and OV fault limits.
Slave phases indicate Power Good in STATUS_WORD once
enabled, unless a master error amplifier fault is detected,
indicating the bussed COMP voltage appears to be too high.
Hardwired PWM Response to I_OUT Faults
Hardwired PWM Response to Temperature Faults
An internal temperature sensor measured by the moni-
tor ADC protects against EEPROM and other IC damage.
When die temperature rises above 130°C, the LTC3882
will NACK any EEPROM-related command except RE-
STORE_USER_ALL and MFR_RESET and issue a CML
fault for Invalid/Unsupported Command. Normal EEPROM
access is re-enabled when die temperature drops below
125°C. Above 160°C, the part shuts down all PWM outputs
until die temperature is below 150°C. Internal temperature
fault limits cannot be adjusted. Writing to the EEPROM
above a die temperature of 85°C is strongly discouraged.
Refer to the Absolute Maximum Ratings for other important
temperature limitations on internal EEPROM use.
The LTC3882 measures average I_OUT from the voltage
across the I_SENSE pins, taking into account the sense resistor
or DCR value and its associated temperature coefficient.
Both are provided by PMBus command or EEPROM values.
An output overcurrent (OC) fault condition is detected by
a supervisor comparator for each PWM output when the
sensed instantaneous current for that channel reaches
its maximum allowed value. Refer to the IOUT_OC_
FAULT_LIMIT PMBus command for details. When an OC
fault is detected the controller immediately disables the
top FET, and the bottom FET is normally commanded on
for the remainder of that PWM cycle.
External temperature sensors may also be monitored by
the onboard ADC. There is no hardwired PWM response
for sensed external temperature faults or warnings.
Hardwired PWM Response to Timing Faults
There is no hardwired PWM response to any timing faults.
TON_MAX_FAULT_LIMIT is the time allowed for V_OUT to
rise and settle at start-up. The TON_MAX_FAULT_LIMIT
timer, which has a resolution of 10µs, is started after
TON_DELAY has been reached and a soft-start sequence
is started. If the VOUT_UV_FAULT_LIMIT is not reached or
3882f
For more information www.linear.com/LTC3882
23