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LM5056A: LM5056APMHX/NOPB

John Lwin
Prodigy 130 points
Part Number: LM5056A

Hi TI,

I have got incorrect readings for temperature and voltage measurements. I found out that I have got incorrect VREF voltage on pin 15 of LM5056A . I measured VREF and got 4.1 V which is much higher than 3V (max) as per datasheet. I have got ceramic cap 1uF, 6V placed next to the pin. 

I understand that VREF is an internal reference voltage which is generated precisely 2.97V. I would like to know what could cause my VREF higher than expected value. 

Looking forward to your reply.

Regards,

  • 0
    TI__Mastermind 31685 points

    Hey John,

    You're right that you should not be seeing 4.1V at Vref pin. Could you send us the schematic for how your are configuring the device? Also, are you able to get correct input voltage or readings? Or is the Vref affecting this? If you have any package or lot information please send this information as well.
     
    Sincerely,
    Peter Iliya
    Current Sensing

  • 0 in reply to Peter Iliya
    Prodigy 130 points

    Hi Peter,

    Thanks for your reply. At this moment I am using this chip to measure input voltage and Temperature only. I preserve current and power measurement for next generation of our products. My theory on your chip is : there must be current threshold for  the chip's Vref internal regulator in order to get correct voltage range. I have experience on other TI chips about current through REF pin got influence on the voltage of VREF. At this point of time I just put 3.9k at Vref pin to gnd in parallel with ceramic cap 1uF that draws around 0.75 to 1 mA from Vref. After putting this resistor, I got my Vref 2.97V and my input voltage and temperature readings are correct.

    I just want to know would there be any side effect for doing this configuration. Please correct me if my theory is wrong and advise me better solution for my case. Is there any issue for this chip if I leave these pins [pin1 (OUT), pin 3 (SENSE) & Pin 4 (VIN_K)] open. Kindly let me know your opinion.

    Regards,

    John

     

  • 0 in reply to John Lwin
    TI__Mastermind 31685 points
    Hello John,

    Leaving the OUT, SENSE, and VIN_K pin should not affect performance. If you remove the VREF 3.9kOhm resistor does the VREF pin rise back up to 4.1V?

    Sincerely,
    Peter Iliya
    Current Sensing Applications
  • 0 in reply to Peter Iliya
    Prodigy 130 points

    Hi Peter,

    Yes, it does even after replacing new LM5056A chip. If this configuration is not affecting chip's performance, it is good for now. Thanks.

    Regards,

    John