Hi all,
My output voltage deviates from the set point and is load dependent. The set point is 48 V and the voltage is between 48 V and 52 V.
I am using the evaluation board for the LT8390A (EVAL-LT8390A-AZ).
The boards comes with a default configuration of 2 Mhz switching frequency and 24 V output voltage. I need in my application a 48 V output voltage from 40 V to 50 V input voltage.
I have changed the voltage divider resistor R5 from 232 kOhm to 470 kOhm what should give me 48 V output voltage.
I reduced the switching frequency to 1 MHz to reduce the losses in the controller chip from the higher input voltage.
I replaced the 680 nH inductor with a 4.7 uH version to limit the current ripple.
The converter is working an I can use it over my required load range (up to 6 A load current).
But my output voltage deviates from the setpoint at varies between 48 V and 52 V depending on the load.
At no load: The output capacitance is charged in bursts from 48 V to 52 V. The burst is ~2ms load and consists of shorter burst packages. When the converter reaches 52 V, the converter stops switching and the output capacitance slowly discharges.
At 200 mA load current does the converter switch continuously. The output voltage is continuously at 52 V.
With increased load current does the output voltage drop and stabilises above 1 A load current at 49 V.
The FB pin voltage follows the output voltage and is between 1 V and 1.05 V.
I increased the output capacitance and changed the voltage control loop capacitor. Both had no impact on the voltage level.
My suspicion is, that the switching noise influences the voltage control (converter starts switching at 48V in low load condition). I added a 100 pF capacitor across R6 (FB low side resistor) but this also did not change the behaviour.
Has someone similar experience with the device or the evaluation board?
What can I do to stabilise my output voltage?
Kind Regards
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