TPS92691: when vin is close to 50V, is there a better place for Rsense?

Frank(EP) Liu

Part Number: TPS92691

hi ,

my customer uses TPS92691 for laser driver. The vin is 50V. They use "Buck-Boost LED Driver" topology for ~60Vout as below.

they have concern on CSP\CSN. these pins only can take 60V.

Are there better place for RCS to get lower voltage?

Another question, if put Q2 at LED- end, is there any concern?

BR,

frank

over 4 years ago

0 Tuan Tran74 over 4 years ago

TI__Mastermind 18890 points

Hi Frank,

What is the Laser Diode voltage? What do you mean by putting Q2 at the LED end? The key is not to exceed the voltage rating on the part.

Thanks Tuan

0 Frank(EP) Liu over 4 years ago in reply to Tuan Tran74

TI__Expert 4830 points

hi Tuan,

the forward voltage is 4V. They will put different laser in series for different model. They want to use one laser drive board. so, the Laser voltage will be 3x~6x V.

They want to put the Q2 before Rcs if there is no side effect. They don't need to reserve too much Vds for p mos.

understood for voltage rating. that's what they have concern. If there is no better place for Rcs, they need to be careful to be over 60V on CSP\CSN.

BR,

frank

0 Tuan Tran74 over 4 years ago in reply to Frank(EP) Liu

TI__Mastermind 18890 points

Hi Frank,

If input if always above output voltage required then they can use a Buck topology on Figure 27. Please note that the CSP and CSN feedbacks are wrong and reversed in this figure.

Thanks Tuan

0 Frank(EP) Liu over 4 years ago in reply to Tuan Tran74

TI__Expert 4830 points

hi Tuan,

thanks for note.

the vin is around 50V and Vout is 3x-6x.

any other suggestion to place the Rcs? And any concern to place the Q2 before Rcs?

BR,

frank

0 Tuan Tran74 over 4 years ago in reply to Frank(EP) Liu

TI__Mastermind 18890 points

Frank,

I am recommending the Buck topology for their application and not the Buck Boost. Then the voltage is always less than VIN and you do not have any issue with Rcs placement. I hope you understand that.

Thanks Tuan

0 Frank(EP) Liu over 4 years ago in reply to Tuan Tran74

TI__Expert 4830 points

Tuan,

Vin is 50V and VLED is 3x to 6xV. so, they need buck boost, right?

7 laser diodes in series is 28Vf.

16 laser diodes in series is 64Vf.

BR,

frank

0 Caroline Fuschino over 4 years ago in reply to Frank(EP) Liu

TI__Intellectual 1675 points

Hi Frank,

One of our engineers will help you with this question within 24 hours. In the meantime, please feel free to explore the technical details of all of our parts on the Automotive LED Driver portion of ti.com.

Best Regards,

Caroline

0 Tuan Tran74 over 4 years ago in reply to Caroline Fuschino

TI__Mastermind 18890 points

Frank,

When you mentioned that the load is 3x~6x with 4V led voltage, I understood that as the range of output voltage is 12V to 24V. But if the output voltage range is higher then you might consider a SEPIC topology.

Thanks Tuan

0 Tuan Tran74 over 4 years ago in reply to Tuan Tran74

TI__Mastermind 18890 points

Frank,

You can also use the Boost to Battery with the Rcs location as it is in the block diagram. Q2 can be as it is but be sure to have appropriate voltage rating on Q2. The main mis-understanding that I have with your communication is that I thought the LED voltage is less than Vin and that's why I recommend the Buck topology initially.

Thanks Tuan

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TPS92691: when vin is close to 50V, is there a better place for Rsense?