Modifications to module 1060A DC-DC Converter with XL6019

The operation of the 1060A module is described on the page “DC-DC Step-Up Power Converter module 1060A with the XL6019.” You can find the page here. Basically, Vout is set using an adjustable potentiometer, which is rather inconvenient for a variable power supply.
Since there was a need for an adjustable output voltage ranging from 4.5V to 28V, the values ​​for resistors R1 and R2 (see datasheet and schematic) were recalculated. The starting point was to use a 100k variable potentiometer for R2; however, it turned out that the PWM control did not function correctly with R2 = 10K set to 100k. The module produced after replacement a very high output voltage and became uncontrollable when the variable potentiometer R2 value changed. The cause was that the XL6019’s PWM control circuit had gone out of control; The control loop showed instability.

Possible causes include:

1. Incorrect values ​​in the feedback divider
   The voltage divider (R1, R2) that measures the output voltage for the FB pin must be properly tuned. If the values are too high or too low, the control loop may become unstable. Use standard values ​​for the divider—e.g., R1 = 1k–10k and R2 = 10k–100k.
2. Parasitic effects
   Rapid changes in feedback can introduce noise or inductive effects. Ensure the feedback pin is decoupled using a 10pF–100pF capacitor.
3. Instability in the control loop
   The XL6019 uses a PWM control loop to stabilize the output voltage. If the feedback voltage changes too quickly, the control loop may not respond fast enough
4. Insufficient bulk capacitors at the output
   If the output capacitor (Cout) is too small, the voltage may not stabilize quickly enough during rapid changes.

Calculations for R1 and R2, supported by experimental results, indicate that for an input voltage (U_in) of 4.5 V and an output voltage (U_out) of 28 V, the value for R1 should be 3K3 kΩ, while R2 should be between 10 kΩ and 60 kΩ. This implies the use of a 50 kΩ variable potentiometer.
R1 is also decoupled using a 100 pF capacitor.

See also the diagram below.

The formula for calculating R1 and R2/RV2 can be found alongside, and can be found in the XL6019 datasheet.
The formula has been rearranged in such a way that the result is the value of resistor R2-RV2.

Here are some results of the measurements performed on the modified module.
U_in = 3.7V PWM is out of control, meaning that V_out is undefined and high (>30V) and I_in is >400 mA.
U_in ≥ 4.0V PWM is in control. This means that the output voltage (U_out) can be adjusted from 5V to 23.8V using RV2. The input current with no load on the output ranges from 10mA to 130mA.
Increasing the input voltage (U_in) to 5V reduces the quiescent current, which makes sense, because the PWM control has less work to do.

Additional measurements were taken to observe the ripple effect of the PWM control on the XL6019’s feedback (FB) pin and on the output voltage (U_out). Without the decoupling capacitor on the FB pin, the ripple on the output voltage is significantly higher. The photos above were taken with no load connected to the output.