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TPS7A8300: Characteristics when input/output voltage difference is small

Taito Takemura
Intellectual 2130 points
Part Number: TPS7A8300

Hi experts,

Could you please tell me the TPS7A8300 characteristics below when input/output voltage difference is small?

(1) Is it possible to output Vout=1.2V under the conditions of with BIAS, Iout=0.085A, Vin=1.3V?

(2) There is a graph of PSRR when Vout = 1.2V, Vbias = open, Iout = 1.5A in the data sheet, but could you tell me the PSRR information when 1.3V is input with BIAS?

(3) If the input/output voltage difference is small, are there any characteristics other than dropout voltage and PSRR that we should be aware of?

Thank you for your help.

Best Regards,

Taito Takemura

  • 0
    TI__Genius 12511 points

    Hi Taito,

    (1) Yes, the Dropout for this part does not exceed 300mV even at temperature. With 1V of headroom the device will operate.

    (2) We do not have a specific graph for these exact conditions, but as you can see from the graphs given, the shape is relatively the same across conditions, the level is what shifts. In your specific case, Vin is lower than the lowest which will negatively impact the graph shifting the low and midband frequencies to lower quantities, while the high frequency will not have a significant effect. Additionally this is at 1.5A by decreasing the load current to 85mA you will see a step up in PSRR performance. PSRR can also be increased by suppling the BIAS rail and not leaving it open.

    (3) When the headroom on the LDO is very small, Transient performance, such as line and load regulation, are degraded and VOUT will have larger, and subsequently worse, responses to the transient conditions.

    Regards,

    John

  • 0 in reply to John Schneider
    TI__Intellectual 2130 points

    Hi John,

    Thank you for your answer.

    PSRR can also be increased by suppling the BIAS rail and not leaving it open.

    When inputting 1.3V to 1.4V with bias, will PSRR in the low and midband frequencies improve to the same extent as at 1.5V?

    Best Regards,

    Taito Takemura

  • 0 in reply to Taito Takemura
    TI__Genius 12511 points

    Hi Taito,

    By using BIAS rail to power the device, you will see improvements in the low and midband frequencies, not in the highband as those are dominated by parasitic frequencies. However as you are close to dropout, the 1.3 and 1.4V VIN operation will still have worse performance than 1.5V Vin. 1.4V should appear closer with VBIAS supplied but there will still be differences with this part. 

    Regards,

    John