LTC3859AL_15 Datasheet, PDF (12/44 Pages) Linear Technology – Triple Output, Buck/Buck/Boost Synchronous Controller with 28A Burst Mode IQ

LTC3859AL
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 LTC3859AL 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 LTC3859AL regulates the
V_FB3 voltage to the smaller of 1.2V, or the voltage on the
SS3 pin. An internal 5µA pull-up current source is con-
nected 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 LTC3859AL
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 with this control voltage.
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 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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