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

155 days

SW1

BOTB_DRAIN

FREQ

BOOST2

TOPD_SOURCE

RUN

BOTC_SOURCE

SENSEN

BG2

PGOOD

BOTC_DRAIN

I_AVGSNSN

BOOST2

V_FB

BOOST1

I_AVGSNSP

TOPA_SOURCE

MODE

SW2

BOTB_SOURCE

PGND

SENSEP

ITH

SGND

PILLIN

SW2

V_OUTSNS

TG2

TOPD_DRAIN

Resistance

10kΩ

R10

Resistance

12.1kΩ

Resistance

100 Ω

Resistance

100 Ω

R19

Resistance

100 Ω

R12

Resistance

100 Ω

Inductance

15uH

Resistance

4mΩ

C444

Capacitance

10nF

R13

Resistance

4mΩ

C25

Capacitance

10uF

Capacitance

.22 uF

C16

Capacitance

4.7µF

C12

Capacitance

10uF

Manufacturer Part Number

GRM033R60J224KE15D

Designator Prefix

Capacitance

.22 uF

C10

Capacitance

10uF

C14

Capacitance

220pF

C11

Capacitance

100pF

Reviews

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Project Name

480W, 48V Buck Boost

Description

99% Efficient 480W, 48V Output, 20V to 100V Input Buck-Boost Converter,

Properties

Properties describe core aspects of the project.

Pricing & Availability

Distributor	Qty 1
Digi-Key	$28.96–$35.90
LCSC	$61.99
Mouser	$25.22

Controls

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notbruno / 480W, 48V Buck Boost

Schematic