LTC3875_15 Datasheet, PDF (8/44 Pages) Linear Technology – Dual, 2-Phase, Synchronous Controller with Low Value DCR Sensing and Temperature Compensation

LTC3875
Pin Functions
TK/SS1, TK/SS2 (Pin 1, Pin 8): Output Voltage Tracking
and Soft-Start Inputs. When one channel is configured to
be the master, 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, the feedback
voltage of the master channel is reproduced by a resistor
divider and applied to this pin. Internal soft-start currents
of 1.25µA charge these pins.
V_OSNS1+, V_OSNS2+ (Pin 2, Pin 6): Positive Inputs of Remote
Sensing Differential Amplifiers. These pins receive the
remotely sensed feedback voltage from external resistive
divider across the output. The differential amplifier out-
puts are connected directly to the error amplifiers’ inputs
internally inside the IC.
V_OSNS1–, V_OSNS2– (Pin 3, Pin 7): Negative Inputs of Re-
mote Sensing Differential Amplifiers. Connect these pins
to the negative terminal of the output capacitors when
remote sensing is desired. Connect these pins to local
signal ground if remote sensing is not used.
I_TH1, I_TH2 (Pin 4, Pin 5): Current Control Threshold and
Error Amplifier Compensation Points. The current com-
parators’ tripping thresholds increase with these control
voltages.
TAVG (Pin 13): Average Temperature Summing Point. Con-
nect a resistor to ground to sum all currents together for
multi-channels or multi-IC operations when temperature
balancing function is enabled. The value of the resistor
should be the TRSET resistor value divided by the number
of channels in the system. Float this pin if thermal balanc-
ing is not used.
FREQ (Pin 15): There is a precision 10µA current flowing
out of this pin. A resistor to ground sets a voltage which
in turn programs the frequency. Alternatively, this pin can
be driven with a DC voltage to vary the frequency of the
internal oscillator.
IFAST (Pin 17): Programmable Pin for Fast Transient Op-
eration for Channel 2 Only. A resistor to ground programs
the threshold of the output load transient excursion. Float
this pin to disable this function. See the Applications
Information section for more details.
ENTMPB (Pin 18): Enable Pin for Temperature Balanc-
ing Function. Ground this pin to enable the temperature
balancing function. Float this pin for normal operation.
PGOOD (Pin 19): Power Good Indicator Output. Open-drain
logic that is pulled to ground when either channel’s output
exceeds ±7.5% regulation window, after the internal 20µs
power bad mask timer expires.
EXTV_CC (Pin 24): 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 make sure that EXTV_CC < V_IN at all times.
INTV_CC (Pin 25): Internal 5.5V Regulator Output. The con-
trol circuits are powered from this voltage. Decouple this
pin to PGND with a minimum of 4.7µF low ESR tantalum
or ceramic capacitor.
V_IN (Pin 26): Main Input Supply. Decouple this pin to
PGND with a capacitor (0.1µF to 1µF).
BG1, BG2 (Pin 27, Pin 23): Bottom Gate Driver Outputs.
These pins drive the gates of the bottom N-channel
MOSFETs between INTV_CC and PGND.
BOOST1, BOOST2 (Pin 28, Pin 22): Boosted Floating
Driver Supplies. The (+) terminal of the booststrap capaci-
tors connect to these pins. These pins swing from a diode
voltage drop below INTV_CC up to V_IN + INTV_CC.
TG1, TG2 (Pin 29, Pin 21): Top Gate Driver Outputs. These
are the outputs of floating drivers with a voltage swing
equal to INTV_CC superimposed on the switch node voltage.
SW1, SW2 (Pin 30, Pin 20): Switch Node Connections to
Inductors. Voltage swing at these pins is from a Schottky
diode (external) voltage drop below ground to V_IN.
CLKOUT (Pin 31): Clock Output Pin. Clock output with
phase changeable by PHASMD to enable usage of multiple
LTC3875s in multiphase systems signal swing is from
INTV_CC to ground.
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