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LM224: LM224 , I use LM224 in my HID POWER Driver , there some problem about the linearity of LM224 , the consistency about linearity of LM224 is not good ; the sch as the picture, the problem is( 1% device) when the( linearity is 50%),the error is 10%

Andrew Liu74
Intellectual 970 points
Part Number: LM224

LM224 ,  I use LM224 in my HID POWER Driver , there some problem about  the linearity of LM224 , the consistency about  linearity of LM224 is not good ; the sch as the picture, the problem is( 1% device) when the( linearity is 50%),the  error is 10%.  but the normal is  when the( linearity is 50%),the  error is 3%..   please help to review  what may result in it ,many thanks !

  • 0
    TI__Guru**** 157036 points
    Andrew,

    Can you provide a table of input and output voltages? Be sure to identify the measurement locations. Also helpful is supply voltage(s) for the LM224.
  • 0 in reply to Ron Michallick
    Prodigy 10 points

    LM224  Vin=14.5V.

  • 0 in reply to shilong feng
    TI__Guru**** 157036 points

    Shilong,

    The green component values are hard to read, so let me know if I mis-read one. 
    R29 = 4.7k, R32 = 470; RM31 = 680k, RM35 = RM33 = 1k

    Gain of IC3C is variable between 45.8 and 132.5. So pin 8 is (VIN + VIO) * Gain. Where VIO is amplifier's input offset error. However there is limitation that pin 8 can't go lower than about 0.7V because that output has to sink RM35 current that exceeds the NPN sink driver (see data sheet device schematic) 

    Gain of IC3D is -1 and is offset by ADIN voltage (I don't know the value of this voltage). So pin 14 is 2 * ADIN - VIN with the limitation that pin 14 can't go lower than about 0.7V because that output has to sink RM33 current that exceeds the NPN sink driver (see data sheet device schematic) 

    The diode voltage will vary with temperature, linear and logarithmic function of diode current. 

    In summary , I suspect VIO and diode variance as likely causes of perceived gain / offset errors.

    Unfortunately the input range and output equality claim is not enough information to pinpoint a circuit issue.

     

  • 0 in reply to Ron Michallick
    Intellectual 970 points

    Dear , thank you for your help , the sch as below , and the input V, many thanks ~

  • 0 in reply to Andrew Liu74
    TI__Guru**** 157036 points
    Andrew,

    I do not see any new information. Is there an attachment missing?
  • 0
    Guru 140200 points
    Hi Andrew,

    please explain what the circuit does and how you calculate linearity.

    Kai