UCC256301: UCC256301 HV Startup Prolbem

Henry

How did you design your board?  We recommend that you use our excel design calculator http://www.ti.com/lit/zip/sluc634 to verify that there are no errors in your design.

My understanding is that the trouble you are having is that the bias VCC voltage is not being generated.  If you are not sure which variant of UCC25630x to use please review the following selection guide to make sure the variant you are using includes the features you are looking for http://www.ti.com/lit/sg/slyt728/slyt728.pdf.  If you don't need x-capacitor discharge function we recommend you switch to UCC256302 or UCC256303

The way that the self bias startup for UCC256301 works is that the HV pin acts as a current source to charge the VCC capacitor up to the enable threshold.  This is explained in section 7.4.2 (page 32) of the datasheet.  In your schematic it appears that HV pin is connected to AC line and neutral, so you must have an source connected to the AC terminals for it to startup.  If you are applying a voltage there and you do not have a voltage increasing on VCC, I recommend you verify that the AC input voltage is making it to the IC.

For new designs we recommend you consider our next generation LLC controller UCC256403/4.  The following app note explains the benefits this new IC provides http://www.ti.com/lit/an/slua966/slua966.pdf

Best Regards,
Eric

I only have the basic swithing principles, at uni they don't offfer any advanced courses. Since the PHD project supervisor has litte exprience with optocouppler design and zero exprience with LLC design, I ended up learning using online materials.

I designed the board using HV traning guide from TI, PDF files on LLC tutorial design on semi, infineon, TI. Also using all the tehcnical documents provided for the UCC256301 chip.

I used the spread sheet to design the schematic, but also used formulas to calculate and verify that the transformer design is correct. I have a confidence level of 100% working before I started creating a PCB. I also created a list of VCR capacitors to use, so the transient response can be fine tuned. I coppied the optocoupler design from webench and going to fine tune the actuall values for transient response. I also have looked at opto design guides however it requires measuring of the actuall system operating and working to get the values calculated, so I'm doing trial and error instead.

My understanding of the VCC voltage from datasheet and design guidelines.

Is that only 2 diodes from ac and a resistor connected to HV pin, and connecting the IC to GND and providing a VCC capacitor is that only reqired to generate a VCC voltage. Regardless of whats going on in otherparts of circut.

Once the VCC voltage is generated from AC input, the controller will detect if theres any fault conditon, if not then the chip will start switching.

Otherwise is there any extra circuitry reqruired that is not mentoned in the datasheet.

Can someone please confirm or tell me the connecteion for the VCC generateion from AC input. 

Currently I'm at the conclusion that there is something went wrong with the TI quality control for unseen circumstances, and I have been sent a faulty chip, the chip has been purchased from mouser.

My plan is to purchase both UCC256302 and 256303 to see if I can get the SMPS going at all. 

1st time installing the IC chip soldered by hand and was fairly quick to not overheat it. 

2nd time ESD precautions and proper SMD installation mehtods was used. 

Is the UCC25630x ICS very senstitive to ESD and or requrie a custom baking temeprature profile to get it working. The standard baking profile was used and it expriences max temp of 250C ramping from 200C in 30s and ramping down back to 200C in 30s. I don't have the actuall temperatiure profile on me but I can get it if it helps.

I have confirmed there is ac input by measuring 230V AC at the diodes input on the PCB, however I have not checked the ciurrent at all into the HV resistors since I don't see how this will help.

I also had measured the capacitance from HV pin to GND on the controller IC pad when the IC is removed, the capacitance is about 20pF with a moderate accuracy capacitance meter.

I was half way in designing the circuit before the new LLC I came out, we don't mind having a slightly older IC to be used in a prodcution amplifier.

SInce the current build is only a rough testing one, the final one will be implemented using mostly SMD components, at the time the new IC could possible be considred but depends on pricing and avalibilty of the new LLC IC. 

Thanks

Henry

If you have not already, I recommend that you review the following material that goes over fundamental for resonant LLC topology and our UCC25630x IC

Design HB LLC Converter: https://www.ti.com/seclit/ml/slup263/slup263.pdf

Design and Optimization of a High-Performance LLC Converter: https://www.ti.com/seclit/ml/slup306/slup306.pdf

LLC Converter Small Signal Modeling: https://www.ti.com/seclit/wp/slup330/slup330.pdf

Maximize Efficiency of LLC: https://training.ti.com/maximizing-efficiency-your-llc-power-stage?cu=1134585

Improving Transient Response in LLC Converters Using Hybrid Hysteretic Control http://www.ti.com/lit/an/slua834/slua834.pdf

UCC25630x Practical Design Guidelines: http://www.ti.com/lit/an/slua836a/slua836a.pdf

I also recommend ordering our EVM http://www.ti.com/tool/UCC25630-1EVM-291 so you can power up and measure a known good design.

As for your question on how VCC is generated, it works by having the HV pin act as a high voltage current source that charges VCC.  In UCC256301 there is a FET that is configured to act as a current source, so when a voltage is applied to it, it will provide a charging current for VCC.  Once VCC reaches the UVLO turn on threshold, the FET is turned off, disabling the current source and UCC256301 is enabled.  The switching action will cause the aux winding to generate the VCC power that will drive UCC256301.  If you do not have any voltage on VCC, we recommend that you verify that there is a voltage being applied to HV pin.  If there is and VCC is still not coming up, we recommend you verify that there is no short (such as failed component or solder bridge) that is holding VCC to GND.

Best Regards,

Eric