UCC27211: HS output is not correct

Sara Jia

Part Number: UCC27211

Hi Tis,

We use UCC27211 as the PWM controller for buck DC/DC,the sch is referred by tidrck9.pdf. when HI /LI are set to 0, HS output is 10VDC. if it is correct?

the sch is as follow:

over 7 years ago

0 Don Dapkus over 7 years ago

TI__Guru**** 189401 points

Hi Sara,

Welcome to e2e, and thanks for your interest in our products!

With HI and LI grounded, the switch node, HS, will essentially be floating. So, it is not surprising to me that you see 10V sitting there. It should be a high impedance node, unless you have a low on the other side of L3.

I noticed your D2 - we usually prefer to have this diode on the output side. For more details, please read section "3.4.1 Turn-Off Diode"
of this app note: www.ti.com/.../slua618.pdf

This is the preferred way to add dead-time in hardware.

Let us know if you have any further questions! If this answered your question, please press the green button to let me know!

0 Sara Jia over 7 years ago in reply to Don Dapkus

Expert 2975 points

Dear Don,

Thanks for your reply. Because behind L3,we connected to GND by 10 kohm, So we think it is not right to output 10V .the leak current is about 0.5mA.We test ON's ncp5109,the output is right. So would you pls help us test the result in your Demo Board?

the sch is as follow:

0 Don Dapkus over 7 years ago in reply to Sara Jia

TI__Guru**** 189401 points

Hi Sara,

That's odd, the 10 kohm resistor should discharge any capacitance.

Can you check the gate-source voltage of Q4 to make sure it's turned off? What is the voltage on PV+?

0 Don Dapkus over 7 years ago in reply to Don Dapkus

TI__Guru**** 189401 points

Hi Sara,

We haven't heard from you in a while. Did you get this issue sorted out?

0 Sara Jia over 7 years ago in reply to Don Dapkus

Expert 2975 points

Dear Don,
I will reply soon.
Thanks a lot.

0 Sara Jia over 7 years ago in reply to Sara Jia

Expert 2975 points

Dear Don,
the gate-source voltage of Q4 is turned off . ncp5109 replaced UCC27211 ,the output is right.We think is the IC issue.So would you test it in Demo board to confirm the issue?
Thanks a lot.

0 Don Dapkus over 7 years ago in reply to Sara Jia

TI__Guru**** 189401 points

Hi Sara,

We fully characterized this device before we released it to the market, and MANY people are using it in high-volume applications. The part works as described in the data sheet.

If you can send me some waveforms that show what's going on in your customer's system, I may be able to help.

Please send an oscilloscope shot showing HB-HS, HO-HS, and LO-VSS.

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UCC27211: HS output is not correct