LTC3875_15 Datasheet, PDF (9/44 Pages) Linear Technology – Dual, 2-Phase, Synchronous Controller with Low Value DCR Sensing and Temperature Compensation

LTC3875
Pin Functions
PHASMD (Pin 32): Phase Programmable Pin. This pin can
be tied to SGND, INTV_CC or left floating. It determines the
relative phases between the internal controllers as well
as the phasing of the CLKOUT signal. See Table 1 in the
Operation section for details.
MODE/PLLIN (Pin 33): Forced Continuous Mode, Burst
Mode or Pulse-Skipping Mode Selection Pin and External
Synchronization Input to Phase Detector Pin. Connect
this pin to SGND to force the IC into continuous mode of
operation. Connect to INTV_CC to enable pulse-skipping
mode of operation. Leave the pin floating to enable Burst
Mode operation. A clock on the pin will force the IC into
continuous mode of operation and synchronize the internal
oscillator with the clock on this pin. The PLL compensation
network is integrated into the IC.
RUN1, RUN2 (Pin 34, Pin 16): Run Control Inputs. A volt-
age above 1.22V on either pin turns on the IC. However,
forcing both pins below 1.14V causes the IC to shut down.
There is a 1.0µA pull-up current for both pins. Once the
RUN pin rises above 1.22V, an additional 4.5µA pull-up
current is added to the pin.
ILIM (Pin 35): Current Comparators’ Sense Voltage Range
Input. A resistor divider sets the maximum current sense
threshold to five different levels for the current comparators.
TRSET1, TRSET2 (Pin 36, Pin 14): Input of the Tempera-
ture Balancing Circuitries. Connect these pins through
resistors to ground to convert the TCOMP pin voltages
to currents. These currents are then mirrored to pin TAVG
and are added together for all channels. Float this pin if
thermal balancing is not used.
TCOMP1/ITEMP1, TCOMP2/ITEMP2 (Pin 37, Pin 12):
Input of the Temperature Balancing Circuitries. Connect
these pins to external NTC resistors or temperature sensing
ICs placed near inductors. These pins are used to sense
temperature of each channel and balance the temperature
of the whole system accordingly. When thermal balancing
function is disabled, these pins can be programmed to
compensate the temperature coefficient of the DCR. Con-
nect to an NTC (negative tempco) resistor placed near the
output inductor to compensate for its DCR change over
temperature. Floating this pin disables the DCR temperature
compensation function.
SNSD1⁺, SNSD2⁺ (Pin 38, Pin 11): DC Current Sense Com-
parator Inputs. The (+) input to the DC current comparator
is normally connected to a DC current sensing network.
Ground these pins to disable the novel DCR sensing and
enable normal DCR sensing with five times current limit.
SNS1^–, SNS2^– (Pin 39, Pin 10): AC and DC Current
Sense Comparator Inputs. The (–) inputs to the current
comparators are connected to the output.
SNSA1⁺, SNSA2⁺ (Pin 40, Pin 9): AC Current Sense
Comparator Inputs. The (+) input to the AC current com-
parator is normally connected to a DCR sensing network.
When combined with the SNSD⁺ pin, the DCR sensing
network can be skewed to increase the AC ripple voltage
by a factor of 5.
SGND/PGND (Exposed Pad Pin 41): Signal/Power Ground
Pin. Connect this pin closely to the sources of the bot-
tom N-channel MOSFETs, the (–) terminal of C_VCC and
the (–) terminal of C_IN. All small-signal components and
compensation components should connect to this ground.
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