Datasheet

LTC3880/LTC3880-1
16
3880fc
For more information www.linear.com/LTC3880
OPERATION
OVERVIEW
The LTC3880 is a dual channel/dual phase, constant fre-
quency, analog current mode controller for DC/DC step-
down applications with a digital inter
face. The L
TC3880
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
Individual channels are accessed through the PMBus using
the PAGE command, i.e., PAGE 0 or 1.
Fault reporting and shutdown behavior are fully configu
-
rable. Two individual GPIO outputs are provided (GPIO0,
GPIO1
), both of which can be masked independently
. A
dedicated pin for ALERT is provided. The shutdown opera
-
tion 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 LTC3880 is a constant frequency, current mode step-
down controller containing two channels operating with
various user-defined relative phasing. During normal
operation each 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 each 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