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LMV602: wildly inaccurate when use LMV602

Gump
Intellectual 490 points
Part Number: LMV602

Hi,

Customer use LMV602 for motor current modulating and then send to ADC (built-in MCU). 

Schematic and Input/output wave form please reafer to attachment. 

Cusotmer use about 400pcs LMV602, and found a dozen output error were wildly- up to 0.4V, they use SD06(3 PEAK) to replace LMV602,the problem is resolved. SD06 dose have better perfermance, but LMV602 should not so wildly inaccurate. Can you give some suggestions?

7367.wave form.docx

  • 0
    TI__Guru*** 149776 points
    Gump,

    It is not obvious what is the issue. Can you provide correct signals?

    Is VCC for U4B 3.3V or some other voltage?
    Is ~SD pin connected to VCC?

    Pin 5 has a low level of 0.4V and high level of 2.42V which I assume is correct, although D9 will be passing current so maybe pin 5 VOH should be higher?

    If I read the resistors correctly R55 is 2.2k and R56 is 1K, then gain is 3.2 V/V offset by 0.5V
    Correct output for pin 5 low is (0.4V-0.5V) * 3.2 = -0.32V which would be 0V for U4B GND pin at ground
    Correct output for pin 5 high is (2.42V-0.5V) * 3.2 = 6.144V which would be clamped to VCC