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TPS22968-Q1: Vout rise time

Part Number: TPS22968-Q1
Other Parts Discussed in Thread: TPS22965-Q1, TPS22918-Q1

Hi,

We got a question from customer about TPS22968-Q1.
Could you help us?

[Question]
Our customer considers to use load SW at below condition.

Vin=3.3V
Vbias=3.3V
Iout=2.5A
Vout rise time=5m to 6.6ms

They want the load SW which can be set high accuracy Vout rise time.

- According to TPS22968-Q1 datasheet figure 21, we can see the variation of tr is better than other IC such as TPS22965-Q1.
Is the variation of tr better than other products?

- Can the IC achieve their Vout rise time requirement? If it can't, is there any other products which achieve it?

- How can we estimate the tr at Vbias=3.3V? Could you give us equation at Vbias=3.3V?

Best Regards,
tateo

  • Hi Tateo,

    When you say that you need "high accuracy rise time", what is the acceptable accuracy for the application (ex.50%, 25%)? Do you need the rise time to be accurate across temperature, or do you have a reduced temperature range for the application?

    For your questions:

    - According to TPS22968-Q1 datasheet figure 21, we can see the variation of tr is better than other IC such as TPS22965-Q1.
    Is the variation of tr better than other products?

    The only Q1 load switches we have are the TPS22965-Q1, TPS22968-Q1, and TPS22918-Q1. Judging by the graphs, the TPS22968-Q1 and TPS22918-Q1 have the least  variation across temperature, but the TPS22918-Q1 will not be able to meet your current requirements.

    - Can the IC achieve their Vout rise time requirement? If it can't, is there any other products which achieve it?

    There is no limit on the size of the CT capacitor, but this would also be dependent on the load capacitance. What is the capacitor on the load for this application?

    - How can we estimate the tr at Vbias=3.3V? Could you give us equation at Vbias=3.3V?

    I will take a look at the data we have and provide an equation soon.

    Thanks,

    Alek Kaknevicius

  • Hi Tateo,

    You can use the following equation to estimate rise time at VBIAS=VIN=3.3V:

    tR = 1.48 x CT(pF) + 104

    Please note that this equation does not apply for CT capacitors lower than 100pF and will be more accurate for larger CT capacitor values.

    Thanks,

    Alek Kaknevicius

  • Thank you for your support.
    They need to set Vout rise time between 5msec to 6.5msec at Ta=-40 to 95C. *Rise time is specified 10% to 90% of Voout.
    Can the device meet thier requirement? For exzample, If they set CT=6,200pF(SR=2,195us/V), how much is the variation of SR?

    Best Regards,
    tateo

  • Hi Tateo,

    If the customer is looking for a rise time between 5ms and 6.5ms, then CT=6200pF would be too high. We can calculate for 5.75ms using the equation:

    tR(us) = 1.48 x CT(pF) + 104

    5750us = 1.48 x CT(pF) + 104

    CT = ~3800pF

    To stay within the 5ms to 6.5ms range, there cannot be rise time deviation more than +/-13%. I just looked up some lab data we took across 3 devices, and it looks like for the temperature range of -40C to 105C we see a maximum deviation of 10%. However, we cannot guarantee that the deviation won't be larger since there are many things which can affect rise time (device variation, temperature, CT capacitor variation, board layout).

    Thanks,

    Alek Kaknevicius

  • Hi, Thank you for your support. They understood the IC can't meet thier requirment. But they have to control rise time.
    They consider allowable spec. So they would like to know the variation of rise time which is set approximatly 5.8msec by TPS22968-Q1 and TPS22965-Q1.
    They think load SW IC is better rise time accuracy than discrete circuit. So they want to know the variation and consider allowable spec.

    Best Regards,
    tateo