Datasheet LTC3855 (Analog Devices) - 9

LTC3855 pin FuncTions
(FE38/UJ40) ITEMP1, ITEMP2 (Pin 2, Pin 1/Pin 37, Pin 36):
Inputs of
DIFFP (Pin 14/Pin 10):
Positive Input of Remote Sens- the temperature sensing comparators. Connect each of ing Differential Amplifier. Connect this to the remote load these pins to external NTC resistors placed near induc- voltage of one of the two channels directly. tors. Floating these pins disables the DCR temperature
DIFFN (Pin 15/Pin 11):
Negative Input of Remote Sensing compensation function. Differential Amplifier. Connect this to the negative terminal
RUN1, RUN2 (Pin 3, Pin 17/Pin 38, Pin 13):
Run Control of the output capacitors. Inputs. A voltage above 1.2V on either pin turns on the IC.
DIFFOUT (Pin 16/Pin 12):
Output of Remote Sensing Dif- However, forcing either of these pins below 1.2V causes ferential Amplifier. Connect this to V the IC to shut down the circuitry required for that particular FB1 or VFB2 through a resistive divider. channel. There are 1µA pull-up currents for these pins. Once the Run pin rises above 1.2V, an additional 4.5µA
ILIM1, ILIM2 (Pin 18, Pin 19/Pin 14, Pin 15):
Current pull-up current is added to the pin. Comparator Sense Voltage Range Inputs. This pin can be tied to SGND, tied to INTV
SENSE1+, SENSE2+ (Pin 4, Pin 12/Pin 39, Pin 8):
Current CC or left floating to set the maximum current sense threshold for each comparator. Sense Comparator Inputs. The (+) inputs to the current comparators are normally connected to DCR sensing
PGOOD1, PGOOD2 (Pin 20, Pin 21/Pin 16, Pin 17):
Power networks or current sensing resistors. Good Indicator Output for Each Channel. Open drain logic out that is pulled to ground when either channel output
SENSE1–, SENSE2– (Pin 5, Pin 13/Pin 40, Pin 9):
Current exceeds ±10% regulation window, after the internal 20µs Sense Comparator Inputs. The (–) inputs to the current power bad mask timer expires. comparators are connected to the outputs.
EXTV TK/SS1, TK/SS2 (Pin 6, Pin 11/Pin 1, Pin 7):
Output Volt-
CC (Pin 27/Pin 24):
External Power Input to an Inter- nal Switch Connected to INTV age Tracking and Soft-Start Inputs. When one particular CC. This switch closes and supplies the IC power, bypassing the internal low dropout channel is configured to be the master of two channels, regulator, whenever EXTV a capacitor to ground at this pin sets the ramp rate for CC is higher than 4.7V. Do not exceed 6V on this pin. the master channel’s output voltage. When the channel is configured to be the slave of two channels, the VFB
INTVCC (Pin 28/Pin 25):
Internal 5V Regulator Output. The voltage of the master channel is reproduced by a resistor control circuits are powered from this voltage. Decouple divider and applied to this pin. Internal soft-start currents this pin to PGND with a minimum of 4.7µF low ESR tan- of 1.2µA are charging these pins. talum or ceramic capacitor.
ITH1, ITH2 (Pin 7, Pin 10/Pin 2, Pin 6):
Current Control
VIN (Pin 29/Pin 26):
Main Input Supply. Decouple this pin Thresholds and Error Amplifier Compensation Points. to PGND with a capacitor (0.1µF to 1µF). Each associated channels’ current comparator tripping
BG1, BG2 (Pin 30, Pin 26/Pin 27, Pin 23):
Bottom Gate threshold increases with its ITH control voltage. Driver Outputs. These pins drive the gates of the bottom
VFB1, VFB2 (Pin 8, Pin 9/Pin 3, Pin 5):
Error Amplifier N-Channel MOSFETs between PGND and INTVCC. Feedback Inputs. These pins receive the remotely sensed
PGND1, PGND2 (Pin 31, Pin 25/Pin 28, Pin 22):
Power feedback voltages for each channel from external resistive Ground Pin. Connect this pin closely to the sources of the dividers across the outputs. bottom N-channel MOSFETs, the (–) terminal of CVCC and the (–) terminal of CIN. 3855f Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Related Parts