DAC8775: buck boost converter filtering circuit placement

Ashok Reddy1

Part Number: DAC8775

Hi all,

I am using DAC8775 in my custom design. In the design we are not using HART signal and bypass to ground through the capacitor. We are having place constraints on the PCB. Since we are not using Hart signal, can we place the filtering circuit little bit far from the DAC. Yes mean How much distance is acceptable.

Thanks & Regards,

--Ashok

over 7 years ago

0 Matthew Sauceda over 7 years ago

TI__Genius 11750 points

Hi Ashok,

In the post you mention that you plan to terminate the HARTIN pin by placing a bypass to ground, however you subject title mentions the buck-boost filter circuit. Can you please verify which components you plan to to place away from the DAC8775? A schematic with a circle around any components would be helpful in our review.

Best Regards,

Matt

0 Ashok Reddy1 over 7 years ago in reply to Matthew Sauceda

Prodigy 250 points

Dear Mathew,

The above circuit I want place little bit far from the DAC8775.

Thanks & Regards,

--Ashok

0 Matthew Sauceda over 7 years ago in reply to Ashok Reddy1

TI__Genius 11750 points

Howdy Ashok,

From the picture you have provided, please ensure that D179/D178/L6/C411/C412 components are placed very close to the LN and LP pins. If this recommendation is not followed you may run the risk of degrading power efficiency and creating large inductive peak currents. Additionally, we recommend that you place R1128/1129 close to C411/C412 to avoid large switching noise on the board.

The remaining components can be relaxed in comparison to the above for a layout standpoint. However, it is good practice to place these components close to VPOS and VNEG.

Best Regards,

Matt

0 Ashok Reddy1 over 7 years ago in reply to Matthew Sauceda

Prodigy 250 points

Hi Mathew,

Which are all components I should place near to the VPOS and VNEG.

Thanks & Regards,
-- Ashok

0 Matthew Sauceda over 7 years ago in reply to Ashok Reddy1

TI__Genius 11750 points

Hi Ashok,

To clarify, the remaining components (C413/C414/R575/C415/D177) and (C407/C408/R572/C409/C410/D180) should be placed near their respective VPOS and VNEG pins.

Best Regards,
Matt

0 Ashok Reddy1 over 7 years ago in reply to Matthew Sauceda

Prodigy 250 points

Hi Mathew,

Could you please tell maximum length allowed from Inductor to the DAC. In the evaluation board it is 0.7inches. Can we go upto 1inch. Is this distance is acceptable.

Thanks & regards,
--Ashok

0 Kevin Duke over 7 years ago in reply to Ashok Reddy1

TI__Mastermind 46290 points

Hi Ashok,

It is not necessarily for TI to say whether 1 inch would be acceptable or not. All we can really say is that this would not cause any functional impairments or damage to a device, but it would bear an impact on the efficiency and noise of your system as Matt has mentioned.

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DAC8775: buck boost converter filtering circuit placement