LTC3856 LINER [Linear Technology], LTC3856 Datasheet - Page 9

• Manufacturer Part Number: LTC3856
• Description: 2-Phase Synchronous Step-Down DC/DC Controller with Diffamp
• Manufacturer: LINER [Linear Technology]

pin FuncTions
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
Sense Comparator Inputs. The (+) inputs to the current
comparators are normally connected to DCR sensing
networks or current sensing resistors.
SENSE1
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
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
pin receives the remotely sensed feedback voltage from
an external resistive divider.
I
Amplifier Compensation Point. Each associated channels’
current comparator tripping threshold increases with I
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
TH
FB
(Pin 8/Pin 3): Current Control Threshold and Error
(Pin 7/Pin 2): Error Amplifier Feedback Input. This
+
–
, SENSE2
, SENSE2
+
–
(Pins 3, 13/Pins 31, 7): Current
(Pins 4, 14/Pins 32, 8): Current
(TSSOP/QFN)
FB
voltage
TH
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
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
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
age Range Input. This pin is to be programmed to
SGND, FLOAT or INTV
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
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
Internal Switch Connected to INTV
and supplies the IC power, bypassing the internal low
dropout regulator, whenever EXTV
Do not exceed 6V on this pin and ensure V
at all times.
LIM
(Pin 19/Pin 13): Current Comparator Sense Volt-
CC
(Pin 28/Pin 20): External Power Input to an
CC
to set the maximum current
CC
CC
. This switch closes
is higher than 4.7V.
LTC3856
FB
IN
> V
through a
EXTVCC
CC

3856f
CC
to
,