LTC3883 Datasheet, PDF (15/112 Pages) Linear Technology – Single Phase Step-Down DC/DC Controller with Digital Power System Management

LTC3883/LTC3883-1
Operation
Overview
The LTC3883 is a constant frequency, analog current mode
controller for DC/DC step-down applications with a digital
interface. The LTC3883 digital interface is compatible with
PMBus which supports bus speeds of up to 400kHz. A
typical application circuit is shown on the first page of this
data sheet.Major features include:
n _{Programmable Output Voltage}
n _{Programmable Input Voltage Comparator}
n _{Programmable Current Limit}
n _{Programmable Switching Frequency}
n _{Programmable OV and UV Comparators}
n _{Programmable On and Off Delay Times}
n _{Programmable Output Rise/Fall Times}
n _{Phase-Locked Loop for Synchronous, Polyphase Opera-}
tion (2, 3, 4 or 6 Phases)
n _{Input and Output Voltage/Current, Temperature and}
Duty Cycle Telemetry
n _{Fully Differential Load Sense}
n _{Integrated Gate Drivers}
n _{Non-Volatile Configuration Memory}
n _{Optional External Configuration Resistors for Key}
Operating Parameters
n _{Optional Time-Base Interconnect for Synchronization}
Between Multiple Controllers
n _{Fault Logging}
n _{WP Pin to Protect Internal Configuration}
n _{Standalone Operation After User Factory Configuration}
n _{PMBus, 400kHz Compliant Interface}
The PMBus interface provides access to important power
management data during system operation including:
n _{Internal Controller Temperature}
n _{External System Temperature via Optional Diode Sense}
Elements
n _{Average Output Current}
n _{Average PWM Duty Cycle}
n _{Average Output Voltage}
n _{Average Input Voltage}
n _{Average Input Current}
n _{Configurable, Latched and Unlatched Individual Fault}
and Warning Status
Fault reporting and shutdown behavior are fully configu-
rable using the GPIO output (GPIO). A dedicated pin for
ALERT is provided. The shutdown operation also allows
all faults to be individually masked and can be operated
in either unlatched (hiccup) or latched modes.
Individual status commands enable fault reporting over
the serial bus to identify the specific fault event. Fault or
warning detection includes the following:
n _{Output Undervoltage/Overvoltage}
n _{Input Undervoltage/Overvoltage}
n _{Input and Output Overcurrent}
n _{Internal Overtemperature}
n _{External Overtemperature}
n _{Communication, Memory or Logic (CML) Fault}
Main Control Loop
The LTC3883 is a constant frequency, current mode step-
down controller that operates at a user-defined relative
phasing. During normal operation the top MOSFET is
turned on when the clock for that channel sets the RS latch,
and turned off when the main current comparator, I_CMP ,
resets the RS latch. The peak inductor current at which
I_CMP resets the RS latch is controlled by the voltage on the
I_TH pin which is the output of the error amplifier, EA. The
EA negative terminal is equal to the V_SENSE voltage divided
by 5.5 (2.75 if range = 1). The positive terminal of the EA is
connected to the output of a 12-bit DAC with values ranging
from 0V to 1.024V. The output voltage, through feedback
of the EA, will be regulated to 5.5 times the DAC output
(2.75 times if range = 1). The DAC value is calculated by
the part to synthesize the users desired output voltage.
The output voltage is programmed by the user either
3883f
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