LTC3859_15 Datasheet, PDF (12/42 Pages) Linear Technology – Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller

LTC3859
PIN FUNCTIONS (QFN/TSSOP)
TRACK/SS1, TRACK/SS2, SS3 (Pins 34, 16, 3/Pins 38,
20, 7): External Tracking and Soft-Start Input. For the buck
channels, the LTC3859 regulates the V_FB1,2 voltage to the
smaller of 0.8V, or the voltage on the TRACK/SS1,2 pin. For
the boost channel, the LTC3859 regulates the V_FB3 voltage
to the smaller of 1.2V, or the voltage on the SS3 pin. An
internal 1μA pull-up current source is connected to this pin.
A capacitor to ground at this pin sets the ramp time to final
regulated output voltage. Alternatively, a resistor divider on
another voltage supply connected to the TRACK/SS pins
of the buck channels allow the LTC3859 buck outputs to
track the other supply during start-up.
I_TH1, I_TH2, I_TH3 (Pins 35, 15, 7/Pins 1, 19, 11): Error
Amplifier Outputs and Switching Regulator Compensation
Points. Each associated channel’s current comparator trip
point increases.
V_FB1, V_FB2, V_FB3 (Pins 36, 14, 6/Pins 2, 18, 10): Receives
the remotely sensed feedback voltage for each controller
from an external resistive divider across the output.
SENSE1⁺, SENSE2⁺, SENSE3⁺ (Pins 37, 13, 4/Pins 3, 17, 8):
The (+) Input to the Differential Current Comparators.
The I_TH pin voltage and controlled offsets between the
SENSE^– and SENSE⁺ pins in conjunction with R_SENSE set the
current trip threshold. For the boost channel, the SENSE3⁺
pin supplies current to the current comparator.
SENSE1^–, SENSE2^–, SENSE3^– (Pins 38, 12, 5/Pins 4,
16, 9): The (–) Input to the Differential Current Compara-
tors. When SENSE1,2^– for the buck channels is greater
than INTV_CC, then SENSE1,2^– pin supplies current to the
current comparator.
PGND (Exposed Pad Pin 39): Driver Power Ground. Con-
nects to the sources of bottom (synchronous) N-channel
MOSFETs and the (–) terminal(s) of C_IN. The exposed
pad must be soldered to the PCB for rated electrical and
thermal performance.
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