UCC28910: Voltage drops and voltage fluctuation while connected to load

Agile2 Agile2

Part Number: UCC28910

Hello,

We made our design as per UCC28910 reference design. We want to 5v 1amp outout but when we connect load with smps voltage fluctuations and voltage drops down. We make some changes with respect to original design to get 5V 1amp output. Changes are listed below.

D4 : schottky diode SSC54 instead MBRS3100

http://www.mouser.in/ProductDetail/Diodes-Incorporated/PDS1040L-13/?qs=%2fha2pyFaduhUB551PcVr8bTH9mwG7y%252b9MROImRpGeRn4MNTBeogaBQ%3d%3d

D2 : Diode BAV21W-FDICT-ND instead BAS21HT1G

http://www.mouser.in/ProductDetail/Diodes-Incorporated/BAV21W-7-F/?qs=%2fha2pyFaduh%2fMVI0ak38pv8ELP12NHFhgix0qm5uV9KnL9YYQioevQ%3d%3d

R4: Resistor 22ohm instead 2.2ohm

R6 : Resistor 36K instead 43K

R7 : Resistor 910K instead 620K

R8 : Resistor 62K instead 82K

R8 : Resistor 15K instead 22ohm

R10: Resistor 3.9K instead Not connected

C4 : Capacior 4.7uF instead 10uF

C5 : Capacitor 470uf instead 330uF

C6 : Capacitor 470uf instead 330uF

C7: Capacitor 1000pF instead 0.1uF

We added 33pF capacitor between GND and Drain (Pin no 8) of UCC28910 IC

I have attached reference design and also our design. Please help us to get steady output.tidrco2_Reference Design.pdf

over 6 years ago

0 DavitKhudaverdyan over 6 years ago

TI__Intellectual 880 points

Hi,

In your schematic, the output electrolytic capacitors appear to be backwards. If you intended to have a negative output on pin 1 of P2, then the polarity of the output capacitors are wrong, and can be the cause of your issue.

If you intended a positive output on pin 1 of P2, then both the diode D4 and the winding polarity of the fly-back transformer is backwards.

Please check your circuit for these issues and that any other components are installed properly.

0 DavitKhudaverdyan over 6 years ago in reply to DavitKhudaverdyan

TI__Intellectual 880 points

Hi again,

There is an Evaluation Module featuring the UCC28910 with a universal input and provides a 5V,6W output like what you are trying to do that I will link to below. I recommend ordering the evaluation module and copying that design.

Here's the link: www.ti.com/.../ucc28910fbevm-526

0 Agile2 Agile2 over 6 years ago in reply to DavitKhudaverdyan

Prodigy 140 points

Hi DavitKhudaverdyan,

Thanks for your reply.

Sorry I attached old schematic by mistake. Earlier we faced that problem as you said in your comment then we changed our circuit. Now our circuit is same as you said but the problem is as it is, voltage drop down and voltage fluctuation while connected to load. What is the solution for that, your suggestions are valuable for us.

Thank you.

0 DavitKhudaverdyan over 6 years ago in reply to Agile2 Agile2

TI__Intellectual 880 points

Hi Agile2 Agile2,

It may be that your board is hitting over-voltage protection (OVP). OVP is reached if the voltage sample on the VS pin exceeds 4.6V. This can occur any time from t_{LK_RESET} all the way to t_SMPL. If this happens then the device stops switching and reduces current consumption to I_FAULT, slowly discharging the VDD capacitor down to the High Voltage on threshold. Following that the standard startup procedure starts again.

The voltage sample on the VS pin has some requirements for reliable operation, including the reset time of the leakage inductance and the duration of any subsequent leakage inductance ring. Following t_{LK_RESET}, the peak-to-peak voltage at the VS pin should be less than approximately 100 mV_p-p at least 200ns before the end of the demagnetization time, t_DMAG.

Our UCC28910EVM User Guide includes waveforms for what the switching signal should look like:

The green waveform is the I_PK voltage and the blue waveform is the drain voltage. The drain voltage and auxiliary winding voltage should look the same except for the voltage levels, where the auxiliary winding will have a lower voltage from the transformer coupling.

Please take some waveforms of your auxiliary winding to see if this is occurring.

I recommend taking a look at the UCC28910EVM as it supports the same specifications that you are looking for.

Additional Resources:

UCC28910EVM: http://www.ti.com/tool/ucc28910fbevm-526

UCC28910EVM User Guide: http://www.ti.com/lit/ug/sluuai4a/sluuai4a.pdf

UCC28910 Datasheet: http://www.ti.com/lit/ds/symlink/ucc28910.pdf