Variable Output Voltage Design

flux

2:14

Evaluating design adjustments.

Confirming voltage specifications.

Discussing component linking.

Confirming LTC3779 specifications.

Accessing knowledge base.

Reviewing the bill of materials.

Looking for "VFB reference voltage" in ltc3779.pdf

Looking for "Output voltage setting equation VOUT VFB resistive divider" in ltc3779.pdf

Looking for "VFB pin description" in ltc3779.pdf

Looking for "Loop compensation ITH component selection guidelines" in ltc3779.pdf

Looking for "PGOOD threshold relative to VFB regulation" in ltc3779.pdf

Looking for "SS pin soft-start description" in ltc3779.pdf

Looking for "VOUTSENSE pin function and remote sensing guidance" in ltc3779.pdf

Looking for "Output voltage range limitations and minimum on/off-time constraints" in ltc3779.pdf

Looking for "VFB reference voltage" in ltc3779.pdf

Looking for "Output voltage programming equation VOUT" in ltc3779.pdf

Looking for "VFB pin description" in ltc3779.pdf

Looking for "ITH compensation selection" in ltc3779.pdf

Looking for "PGOOD threshold" in ltc3779.pdf

Looking for "SS soft-start" in ltc3779.pdf

Looking for "VOUTSENSE pin function" in ltc3779.pdf

Looking for "minimum on-time off-time output voltage range" in ltc3779.pdf

Exploring adjustable output options.

Yes. This design can be made variable by changing the feedback divider around U1. Per best practice, the output voltage is set by the feedback resistors, so making one leg adjustable will vary VOUT.
Practical options:
  • Front-panel potentiometer:
    • Keep R10 fixed and replace R11 with a series fixed resistor plus a multi-turn pot to the output. Add “stopper” resistors to enforce safe min/max VOUT. This is the simplest way to vary VOUT.
  • MCU/DAC control:
    • Inject a controlled voltage/current into the FB node with a DAC (through a resistor or small summing amp). This avoids a mechanical pot and enables profiles/limits in firmware.
What to watch:
  • Compensation: Varying VOUT changes plant gain. You may need to retune the ITH network (R9, C11) for stability across the range.
  • Status thresholds: PGOOD/OV/UV thresholds track the FB ratio, so they will shift with adjustable VOUT.
  • Remote sense: Keep VOUT sense wiring as-is; do not route the divider wiper through long runs.
  • Range limits: Define hard min/max with fixed resistors so the pot/DAC cannot drive VOUT into unsafe regions.
  • Power/train limits: Ensure the chosen VOUT range stays within controller minimum on/off-time limits, inductor ratings, and MOSFET/diode voltage stress.
If you share:
  • Desired VOUT range (min/max)
  • Adjustment method (pot vs MCU/DAC)
  • Load current over that range
I can put together a concrete change proposal (values for R10/R11, pot value and end-stops, and any ITH tweaks), and then implement it in the project for you.
Give target range
Prefer potentiometer
Ask compensation impact
MCU/DAC control
Check controller limits
157 days
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