• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 4 answers
  • Subscribers 63 subscribers
  • Views 217 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLV743P: detection frequency

Howard Zou
Genius 12365 points
Part Number: TLV743P
Other Parts Discussed in Thread: TPS7A05

Hi,

my customer is evaluating TLV743P and they raise a strange question.

What's the detection frequency of TLV743P?

They said that to keep the output stable, LDO has to monitor the output voltage at a frequency. Lower detection frequency could result in Low Iq LDO.

But I argue that there is no parameter called detection frequency because the feedback loop is analog not digital.

But I've got no idea why some LDO could achieve low Iq.

I believe it's not something related to detection frequency, right?

  • 0
    TI__Mastermind 29260 points

    Hi Howard,

    "Detection frequency" is not a parameter used when discussing linear regulators.  I'm not sure what they are referring to.  The Iq of an LDO has to do with the internal topology and the current needed to run the internal circuits, especially the current needed to turn on / off the internal pass device.  The following app note might be useful as it discusses how the Iq can change based on whether the internal pass element is a MOSFET or a BJT.

    https://www.ti.com/lit/an/snva020b/snva020b.pdf

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Genius 12365 points

    Stephen,

    then do we have the terminology "high speed LDO"?

    How can we achieve high speed LDO?

  • 0 in reply to Howard Zou
    TI__Mastermind 29260 points

    Hi Howard,

    These terms sound like digital electronics terms as opposed to analog terms.
    Linear regulators have analog building blocks like voltage references, op-amps and the like.  If the datasheet has a phrase like "high speed" it would be referring to high bandwidth of the feedback loop.  The high bandwidth is a function of the internal error amplifier, pass element, output capacitor and feedback resistors if a Cff is used.

    Section 7 of the app note I linked gives a good overview of stability analysis inside linear regulators.
    The customer has control over items like output capacitance and for adjustable regulators, feed forward capacitance across the high side setpoint resistor.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Genius 12365 points

    Stephen,

    then is it true that with higher bandwidth of the feedback loop, the transient response will be faster for load change? And the negative impact is that it will have larger Iq?

  • 0 in reply to Howard Zou
    TI__Mastermind 29260 points

    Howard,

    With a higher bandwidth of the feedback loop, the transient response will be faster for a load change.
    It is not for certain that there will be a larger Iq.  You will want to refer to the datasheet, and I would also lean towards newer linear regulators where the architectures are more complex to improve these types of metrics.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Genius 12365 points

    Stephen,

    after reading the article you provided, it seems that with P-FET LDO, we can naturally get low Iq, right?

    Are there any sacrifice for using P-FET against PNP transistor?

    And are there any other method to decrease Iq of an LDO?

  • 0 in reply to Howard Zou
    TI__Mastermind 29260 points

    Hi Howard,

    Most modern LDO's will be using CMOS as the pass element instead of BJT's.  I think the last BJT linear regulator we designed was somewhere around 10 years ago.  If you use a modern LDO with low Iq, it may have a PMOS pass element.  To achieve even lower Iq you could take advantage of an LDO which has an enable pin, and disable the device anytime you do not need the LDO output to be powering electronics.  The Iq in standby mode (when the device is disabled) is very small.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Genius 12365 points

    Stephen,

    thanks.

    I would like to be specific, TLV743P and TPS7A05 are both new devices(released later than 2017) and both have enable pin.

    But TLV743P Iq=34uA, TPS7A05 Iq=1uA.

    What caused the Iq difference? Are there any trade-off for TPS7A05 to achieve such low Iq?

  • 0 in reply to Howard Zou
    TI__Genius 13085 points

    Hi Howard,

    While there is not a direct correlation between the Iq and the bandwidth (response time), in general a lower Iq device will have a lower bandwidth and will respond to transients less quickly. This is because you need current to charge/discharge the internal nodes/parasitic capacitance and the less current available the longer it takes to charge/discharge. As Stephen mentioned there are some modern circuit techniques/topologies which help improve transient response  even with low Iq. 

    As for the two parts you discussed if you compare the load transient response time and the PSRR roll off in the typical char graphs in the datasheets you can see a difference between the two.