LTC3856 Datasheet, PDF (9/40 Pages) Linear Technology – 2-Phase Synchronous Step-Down DC/DC Controller with Diffamp

LTC3856
Pin Functions (TSSOP/QFN)
FREQ (Pin 1/Pin 29): Frequency Setting Pin. A resistor
to ground sets the operating frequency of the controller.
This pin can also be driven with a DC voltage to vary the
frequency of the internal oscillator.
RUN (Pin 2/Pin 30): Run Control Input. A voltage above
1.22V on this pin turns on the IC. There is a 1µA pull-up
current for this pin. Once the RUN pin rises above 1.22V,
an additional 4.5µA pull-up current is added to the pin.
SENSE1⁺, SENSE2⁺ (Pins 3, 13/Pins 31, 7): Current
Sense Comparator Inputs. The (+) inputs to the current
comparators are normally connected to DCR sensing
networks or current sensing resistors.
SENSE1^–, SENSE2^– (Pins 4, 14/Pins 32, 8): Current
Sense Comparator Inputs. The (–) inputs to the current
comparators are connected to the outputs.
NC (Pins 5, 25, 34) TSSOP Package: No Connections.
TK/SS (Pin 6/Pin 1): Output Voltage Tracking and Soft-
Start Input. When one particular IC is configured to be the
master of two ICs, a capacitor to ground at this pin sets
the ramp rate for the master IC’s output voltage. When the
IC is configured to be the slave of two ICs, the V_FB voltage
of the master IC is reproduced by a resistor divider and
applied to this pin. An internal soft-start current of 1.25µA
is charging this pin.
V_FB (Pin 7/Pin 2): Error Amplifier Feedback Input. This
pin receives the remotely sensed feedback voltage from
an external resistive divider.
I_TH (Pin 8/Pin 3): Current Control Threshold and Error
Amplifier Compensation Point. Each associated channels’
current comparator tripping threshold increases with I_TH
control voltage.
SGND (Pin 9/Pin 33): Signal Ground and Power Ground. All
small-signal components and compensation components
should connect to this ground, which in turn connects to
PGND at one point.
AVP (Pin 10/Pin 4): Active Voltage Positioning Load Slope
Programming Pin. A resistor between this pin and the
DIFFP pin sets the load slope.
ITEMP (Pin 11/Pin 5): Input to the Temperature Sensing
Circuit. Connect this pin to an external NTC (negative
temperature coefficient) resistor placed near the heat
source on the PCB board (e.g., inductors) changes the
controller’s current limit with temperature.
PHASMD (Pin 12/Pin 6): Connect this pin to SGND, INTV_CC,
or float this pin to select the phase of CLKOUT to be 60°,
120° and 90°, respectively.
DIFFP (Pin 15/Pin 9): Positive Input of Remote Sensing
Differential Amplifier. Connect this directly to the remote
load voltage.
DIFFN (Pin 16/Pin 10): Negative Input of Remote Sens-
ing Differential Amplifier. Connect this pin to the negative
terminal of output load capacitors.
DIFFOUT (Pin 17/Pin 11): Output of Remote Sensing
Differential Amplifier. Connect this pin to V_FB through a
resistive divider.
ISET (Pin 18/Pin 12): Stage Shedding Mode Comparator
and Burst Mode Comparator Programming Pin. A resistor
to ground programs the threshold of the Stage Shedding
mode comparator or Burst Mode comparator threshold
and current limit.
I_LIM (Pin 19/Pin 13): Current Comparator Sense Volt-
age Range Input. This pin is to be programmed to
SGND, FLOAT or INTV_CC to set the maximum current
sense threshold to one of three different levels for both
comparators.
MODE (Pin 20/Pin 14): Forced Continuous Mode,
Burst Mode Operation or Stage Shedding Mode Selec-
tion Pin. Connect this pin to SGND to force IC in
continuous mode of operation. Connect to INTV_CC to
enable Stage Shedding mode operation. Leaving the pin
floating enables Burst Mode operation.
PGOOD (Pin 21/Pin 15): Power Good Indicator Output.
Open-drain logic out that is pulled to ground when the
output exceeds the ±10% regulation window, after the
internal 20µs power-bad mask timer expires.
EXTV_CC (Pin 28/Pin 20): External Power Input to an
Internal 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 and ensure V_IN > V_EXTVCC
at all times.
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