LM3489: Questions about LM3489 output capacitor in TPS65987DDJ EVM board

Paul Yeh

Part Number: LM3489

Hi Team,

My customer design portable monitor application and would like to reduce LM3489 output bulk cap value and material because of dimension constraint.

According to EVM board's design, there are 2pcs 47µF Tantalum capacitors 35V .

So can customer change output cap to 2pcs 22uF ceramic capacitor 25V? The system power rating is below 60W

Or please also advise the suitable bulk cap design?

over 5 years ago

0 Paul Yeh over 5 years ago

TI__Genius 16185 points

Hi team,

Customer change output cap material from ceramic to POSCAP. SO now it is 2pcs 22uF POSCAP, please advise, especial for stability concern.

Thanks

0 Iven Su over 5 years ago in reply to Paul Yeh

TI__Expert 8245 points

Hi,

What's the output voltage your customer uses?

0 Paul Yeh over 5 years ago in reply to Iven Su

TI__Genius 16185 points

Iven,

The input voltage is 20V and output voltage will be 5V/3A; 9V/3A; 15V/3A and 20V/3A four setting.

Thanks

0 Iven Su over 5 years ago in reply to Paul Yeh

TI__Expert 8245 points

Hi,

Ceramic capacitors have very low ESRs which are not suitable for this device as output voltage is needed for loop control. If customer wants to use ceramic capacitors they need to add a low value resistor in series. Also 25V rating is too low as DC bias will reduce capacitance a lot.

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LM3489: Questions about LM3489 output capacitor in TPS65987DDJ EVM board