LTC3899_15 Datasheet, PDF (12/38 Pages) Linear Technology – 60V Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller

LTC3899
Pin Functions (QFN/TSSOP)
TRACK/SS1, TRACK/SS2, SS3 (Pins 33, 17, 3/Pins 37,
21, 7): External Tracking and Soft-Start Input. For the buck
channels, the LTC3899 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 LTC3899 regulates the V_FB3
voltage to the smaller of 1.2V, or the voltage on the SS3
pin. An internal 10µA 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 re-
sistor divider on another voltage supply connected to the
TRACK/SS pins of the buck channels allow the LTC3899
buck outputs to track the other supply during start-up.
VPRG3 (Pin 34/Pin 38): Channel 3 Output Control Pin.
This pin sets the boost channel to adjustable output mode
using external feedback resistors or fixed 10V/12V output
mode. Floating this pin allows the output to be programmed
through the V_FB3 pin using external resistors, regulating
V_FB3 to the 1.2V reference. Connecting this pin to GND or
INTV_CC programs the output to 10V or 12V (respectively),
and V_FB3 is used to sense the output voltage.
ITH1, ITH2, ITH3 (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 (Pins 36, 14/Pins 2, 18): These pins receive the
remotely sensed feedback voltage for each buck controller
from an external resistive divider across the output.
V_FB3 (Pins 6/Pins 10): If VPRG3 is floating, this pin receives
the remotely sensed feedback voltage for the boost con-
troller from an external resistive divider across the output.
If VPRG3 is tied to GND or INTV_CC, this pin receives the
remotely sensed output voltage of the boost controller.
SENSE1⁺, SENSE2⁺, SENSE3⁺ (Pins 37, 13, 4/Pins 3,
17, 8): The (+) Input to the Differential Current Compara-
tors. The ITH 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.
GND (Exposed Pad Pin 39/Exposed Pad Pin 39): Ground.
The exposed pad must be soldered to the PCB for rated
electrical and thermal performance.
3899f
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