LTC3855_15 Datasheet, PDF (9/44 Pages) Linear Technology – Dual, Multiphase Synchronous DC/DC Controller with Differential Remote Sense

LTC3855
Pin Functions (FE38/UJ40)
ITEMP1, ITEMP2 (Pin 2, Pin 1/Pin 37, Pin 36): Inputs of
the temperature sensing comparators. Connect each of
these pins to external NTC resistors placed near induc-
tors. Floating these pins disables the DCR temperature
compensation function.
RUN1, RUN2 (Pin 3, Pin 17/Pin 38, Pin 13): Run Control
Inputs. A voltage above 1.2V on either pin turns on the IC.
However, forcing either of these pins below 1.2V causes
the IC to shut down the circuitry required for that particular
channel. There are 1µA pull-up currents for these pins.
Once the Run pin rises above 1.2V, an additional 4.5µA
pull-up current is added to the pin.
SENSE1⁺, SENSE2⁺ (Pin 4, Pin 12/Pin 39, Pin 8): Current
Sense Comparator Inputs. The (+) inputs to the current
comparators are normally connected to DCR sensing
networks or current sensing resistors.
SENSE1^–, SENSE2^– (Pin 5, Pin 13/Pin 40, Pin 9): Current
Sense Comparator Inputs. The (–) inputs to the current
comparators are connected to the outputs.
TK/SS1, TK/SS2 (Pin 6, Pin 11/Pin 1, Pin 7): Output Volt-
age Tracking and Soft-Start Inputs. When one particular
channel is configured to be the master of two channels,
a capacitor to ground at this pin sets the ramp rate for
the master channel’s output voltage. When the channel
is configured to be the slave of two channels, the V_FB
voltage of the master channel is reproduced by a resistor
divider and applied to this pin. Internal soft-start currents
of 1.2µA are charging these pins.
I_TH1, I_TH2 (Pin 7, Pin 10/Pin 2, Pin 6): Current Control
Thresholds and Error Amplifier Compensation Points.
Each associated channels’ current comparator tripping
threshold increases with its I_TH control voltage.
V_FB1, V_FB2 (Pin 8, Pin 9/Pin 3, Pin 5): Error Amplifier
Feedback Inputs. These pins receive the remotely sensed
feedback voltages for each channel from external resistive
dividers across the outputs.
DIFFP (Pin 14/Pin 10): Positive Input of Remote Sens-
ing Differential Amplifier. Connect this to the remote load
voltage of one of the two channels directly.
DIFFN (Pin 15/Pin 11): Negative Input of Remote Sensing
Differential Amplifier. Connect this to the negative terminal
of the output capacitors.
DIFFOUT (Pin 16/Pin 12): Output of Remote Sensing Dif-
ferential Amplifier. Connect this to V_FB1 or V_FB2 through
a resistive divider.
I_LIM1, I_LIM2 (Pin 18, Pin 19/Pin 14, Pin 15): Current
Comparator Sense Voltage Range Inputs. This pin can
be tied to SGND, tied to INTV_CC or left floating to set the
maximum current sense threshold for each comparator.
PGOOD1, PGOOD2 (Pin 20, Pin 21/Pin 16, Pin 17): Power
Good Indicator Output for Each Channel. Open drain logic
out that is pulled to ground when either channel output
exceeds ±10% regulation window, after the internal 20µs
power bad mask timer expires.
EXTV_CC (Pin 27/Pin 24): External Power Input to an Inter-
nal Switch Connected to INTV_CC. This switch closes and
supplies the IC power, bypassing the internal low dropout
regulator, whenever EXTV_CC is higher than 4.7V. Do not
exceed 6V on this pin.
INTV_CC (Pin 28/Pin 25): Internal 5V Regulator Output. The
control circuits are powered from this voltage. Decouple
this pin to PGND with a minimum of 4.7µF low ESR tan-
talum or ceramic capacitor.
V_IN (Pin 29/Pin 26): Main Input Supply. Decouple this pin
to PGND with a capacitor (0.1µF to 1µF).
BG1, BG2 (Pin 30, Pin 26/Pin 27, Pin 23): Bottom Gate
Driver Outputs. These pins drive the gates of the bottom
N-Channel MOSFETs between PGND and INTV_CC.
PGND1, PGND2 (Pin 31, Pin 25/Pin 28, Pin 22): Power
Ground Pin. Connect this pin closely to the sources of the
bottom N-channel MOSFETs, the (–) terminal of C_VCC and
the (–) terminal of C_IN.
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