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LP2985A: desing

Arul Murukesan
Prodigy 40 points
Part Number: LP2985A
Other Parts Discussed in Thread: TLV733P, TLV755P

Hi There,

In our board, after program one particular LED should blink. (Means that board got programmed correctly).

In the below circuit at location IC U4 if we use Microchip brand IC (MCP1801T-2502I/OT) or SHARP brand IC (PQ1X251M2ZPH) means that particular LED is blinking correctly.

C9: - CAP CER 10UF 16V Y5V 0805,

C10: - CAP CER 10UF 16V Y5V 0805,

C11:- CAP .1UF 50V CERAMIC Y5V 0603

 But  if I use TI brand IC (LP2985A-25DBVT) at location U4 means that particular LED is not bilking. But am getting +2.5V correctly. In the same board if i replace Microchip brand IC (MCP1801T-2502I/OT) or SHARP brand IC (PQ1X251M2ZPH) means that particular LED is blinking correctly.

Can you please advice, if I want to use TI brand IC in my board… any components/capacitors values need to change at IC U4 area? Or any other comments on this..?  or Output current is not enough in TI brand ICs(150milliamps)?

Expecting your valuable advice..

 

                        

  • 0
    TI__Expert 4320 points

    Hi Arul,

    I see based off of the schematic that you are running at 300mA, these devices are rated for 150mA. With that being said, it doesn't seem like there is an issue with the IC as you mentioned you are still seeing a +2.5V regulation which is being provided by the LP2985A.

    A suggestion that you can implement is to reduce the 100nF/0.1uF bypass capacitor to the recommended 0.01uF or 10nF capacitor. I believe the 0.1uF came from the Sharp device.

    Also, it doesn't seem like you are using the total Input Voltage range this device provides, you may be able to use a different device if you are just going to be using the LDO in this type of situation. Please confirm and I can recommend another device.

    regards,

    Wilson

  • 0 in reply to Wilson Fwu
    Prodigy 40 points

    Hi Wilson,

    Thanks for your reply.

    Please advice that you  proposed/ recommended device part number.  (if possible  please send free samples 10pcs for my evaluation/testing )

    If suppose am using your new  proposed part in my board means,  still I need to change those capacitance values (or ) no need of change capacitors.

    please advice....

    Best Regards, Arul

  • 0 in reply to Arul Murukesan
    TI__Expert 4320 points

    Hi Arul,

    I recommended the same device you had been using before: LP2985A-25DBVR which you mentioned you had already evaluated. Please confirm whether or not you need the total input voltage range capability of this device. Since there doesn't seem to be any hard requirements aside from providing a 2.5V rail, the TLV733P or TLV755P could also work here but have a recommended operating input voltage range up to 5.5V.

    If you are sticking with the LP2985A then you should change to the recommended cap values as stated in the LP2985A datasheet as I mentioned in my previous post.

    You can request samples through the TI Store: https://tisamples.ti.com/order/tisamples/en/p/product/?p=LP2985A-25DBVR

    regards,

    Wilson