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LMC6492: IC operation at minimum power supply(v+=2.5v)

Part Number: LMC6492

Hello team,

 

I have an inquiry from customer about IC specifications.

 

The minimum supply voltage for this device is V + = 2.5V in the operating condition table. However, all parameters in the DC and AC electrical characteristics tables are specified only for V + = 5V.

 

How is this part checked to ensure IC operation at V + = 2.5v?

The parameter specified with v + = 2.5V is not in the data sheet, but is there a functional test that ensures IC operation at V + = -2.5V in the shipping test?

 

Best regards,

H.Someno

 

  • Hi Hidekazu,

    I agree with you.

    The front page of datasheet says: "Operates from 5V to 15V Supply"

    The section "Operating Conditions" specifiy a operating supply voltage range of "2.5V <= V+ <= 15.5V".

    And some curves show the performance at V+ = 3V.

    Yes, that's really confusing.

    Kai

  • Hi Kai-san,

    Thanks for your reply.

    Please check the following items.

    - What voltage is the minimum V+ for this part?

    - Is it is 2.5v,  tell me whether the operation at V+=2.5V is checked at shipping test actually.

    A customer is reporting that a IC seems to start the operation at round V+=2.9v in case of V+ rising.

    Regards,

    H.Someno

  • Someno-san,

    2.5V operation is not ensured. The table note in the data sheet say this. 

    Figure 1 in the data sheet shows "Supply Current vs Supply Voltage"; below 4V the supply current is not running at the optimal level. The 2.5V point is on the vertical portion of the curves. With normal process variance there can be a small horizontal shift in performance (for this chart) such that 2.5V supply current would be too close to zero to be functional on some.

    In summary, 2.5V is the typical turn on point however, the supply voltage should be at least 5V for ensured device performance.

     

     

  • Hi Ronald,

    Thanks for your reply.

    Now, I understand that this product has not been tested at V+ = 2.5v in shipping test.

    - Is this understanding correct?

    - If so, What is the minimum power supply voltage that can actually guarantee the operation of the IC?

    A year after the start of mass production on the customer's application, the customer found a defect where one of their products did not start working.
    According to customer analysis, the LMC6492 part used in the application appears to have a higher V+ start-up voltage than other components.
    So, customer is worried about changes in IC power supply starting voltage over time.

    -Is there any factor that causes the symptoms that the operation start voltage of the ic power supply(V+) changes with time?

    Regards,
    H. Someno

  • Hi Ron,

    but does TI at least guarantee that the LMC6492 is working down to Vs=3V? See the many figures (7, 10, 11, 15, 18, 19, 23, 25, 29, 36) which show the performance of LMC6492 at Vs=3V.

    Kai

  • Kai,

    I agree that 3V operation is encouraged by those charts. As always, the charts are "Typical Performance Characteristics" in this case at "VS = +15V, Single Supply, TA = 25°C unless otherwise specified". So the 3V chart are 25C data. 

    I did order samples so I could study low voltage operation in more detail. However storm damage has affected my lab so this effort is delayed.

  • Hi Ron,

    that would be nice. Thanks!

    Kai

  • I have samples from 2 lots and tested 5 from each lot.

    I checked power up/down in VOL and VOH state (10mV input drive) for common mode at V- and common mode at V+ and have mostly consistent results on all samples. My load was 100k to mid supply rails, V+/2.

    Here is VOUT vs V+ sweep. Starting just above 0V, the output is high impedance. Near 1.0V on one lot and near 1.5V on the other the output goes low for both VOL and VOH setups. So I expect all devices output low sometime before the device starts running from the input voltage. The normal 'follow the input' point happens near 2.2V for all tested samples. On the power down sweeps, the output goes into the always low state around 2.2V then goes hi-Z around 0.6V for both lots.          

    For completeness. I also checked linear mode unity gain (input = 1/2 V+) with load terminated to V- (ground)

    VOUT vs V+ again.

    For fun, I also checked linear mode unity gain (input = 1/2 V+) with load terminated to V+ 

    VOUT vs V+ again.

    I did see significant variance for the power up to VOL state, but the supply voltage for normal state is pretty tight near 2.2V

    In summary, 3V operation should be fine. 2.5V doesn't have a lot of margin. The device prefers VOL state when used with too low of a supply voltage; this is generally better than the alternative of preferring VOH state. 

  • Hi Ron,

    thank you for your measurements! I appreciate it very much!

    Kai