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ONET1130EC: 2 question about ONET1130EC

Hale Tan
Expert 3770 points
Part Number: ONET1130EC


Hi team,

We have 2 question about 1130EC.

The first one: Assume that the bias pin of the 1130EC is short-circuited to ground. What is the maximum bias current? The maximum bias current output written in the specification is 150mA. Will it exceed this current value?

There is another question, what is the corresponding relationship between BIAS DAC and ADC? We found that the BIAS current calculated through the BIAS DAC is different from the current calculated through the bias ADC. BIAS DAC is set through register 15, open loop mode The bias ADC is calculated by register 40 reading back the ADC. The problem we are encountering now is that in open loop mode, the BIAS DAC (register 15) is set to 0X2A0, and the corresponding current is about 98mA, but the ADC value read back through the bias ADC (register 40) is 0X2AF, and the current is calculated is about 132mA, the results are different.

  • 0
    TI__Expert 3770 points

    Are the differences caused by test or calculation?

  • 0 in reply to Hale Tan
    TI__Guru* 93570 points

    Hi Hale,

    1). Max bias current is 150mA typically. Up to 160mA has been observed - based on part to part variation. Please note figure 13 of the data sheet.

    2). It is possible it could be due to both test and calculation. For calculation. Perhaps this could be due to part to part variations across many parts.

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Expert 3770 points

    Nasser,

    maybe the questions are not clear, I didn't get the answer.

    So the 1st question is: if I short the bias of the device ONET1130EC to the GND, how much is the short current?  And just want to make sure, will it exceed the max limits?

    The 2nd question is: We use the DAC to control the bias, the calculation is as below:

    In open loop mode, the BIAS DAC (register 15) is set to 0X2A0 and the current may be 98mA, is that right?

    And we use ADC value to read back through the bias ADC (register 40) which is 0X2AF, and the current is calculated is about 132mA as below, is the calculation right?

    So the results are different. First could you help to make sure the calculation is right? Second if the calculation is right, maybe the test exists issue or our devices test precision exists issue.

    We need your confirmation to tell how to move forward this case. We are facing the customer pressure, so please kindly support us as much as you can. Thanks in advance.

  • 0 in reply to Nasser Mohammadi
    TI__Expert 3770 points

    Nasser,

    And add another question about onet1130: we think that onet1130 tosa control end and onet1131 tosa control end are the same. But there is a little difference between them about the Ibias. onet1130 ibias unit is 156uA and the onet1131 unit is 147uA. Could you explain the reason?

  • 0 in reply to Hale Tan
    TI__Guru* 93570 points

    Hi Hale,

    1). It depends whether we are operating in open loop or closed loop. If we are in open loop yes we may exceed bias current. In APC mode we will not exceed and it sets fault flag,

    2). Assuming we are using 0x2A0 for table 18(TXBIAS9:TXBIAS2) and table 19(TXBIAS1 and TXBIAS0), then we expect 104mA in open loop mode. 

    Secondly, if we are 0x2AF, then calculation is correct we are reading about 133mA.

    Given expected value of 104mA vs 133mA, i was expecting a closer correlation. Please send me device register settings so we can review.

    3). Internal bias generation on these two devices are different and this is why we have 147uA for ONET1131 and 156uA for ONET1130.

    Regards, Nasser