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BQ24640: power management circuit to absorb current spikes

Kitong-H
Prodigy 100 points
Part Number: BQ24640

I want to extend a measuring device by an interface to an active external sensor. My device is USB powered
and transmits its output data via the USB interface. The external sensor draws its power from the device, so
that the (limited) USB power is splitted to the device as well as to the sensor. The USB power is sufficient to
drive both, the device and on average the sensor. But the problem is that the active sensor draws huge and
sharp current spikes periodically, that causes interferences on VBUS.

Now I need a power management circuit to place in front of the sensor, with following requirements:
- continous current flow at its input (no spikes)
- energy buffering
- high current capability (short-term) at its output to satisfy the current demand during the spike phase

without affecting the countinous input current flow

Sensor behaviour:
- Spike width: 20ms
- Bias current: 50mA
- Spike peak: 200mA
- Sensor voltage: 5V

  • 0
    TI__Mastermind 24075 points
    Hi Kitong,
    BQ24640 is High-Efficiency Synchronous Switched-Mode Super Capacitor Charger. I am unsure how this could be used in your application. Here is the link to the d.s : www.ti.com/.../bq24640.pdf
    Could you give me more information on how you plan to use BQ24640 in your system?
  • 0 in reply to Kedar Manishankar
    Prodigy 100 points

    I am also not sure whether the BQ24640 is a suitable component to solve my issue, so I would like to ask you to recommend an alternative circuit. The goal is to get a power source circuit which provides at its output enough current for the spikes whereas at its input an approximate continous current flows (blue graph 'Average'). To accomplish this the circuit should contain an energy buffer (e.g. supercap). Note that the spike current must come from this power source circuit and must not affect the input current.

  • 0 in reply to Kitong-H
    TI__Mastermind 24075 points
    HI Kitong,
    A supercapacitor is a possible use to supplement the current for frequent charge/discharge cycles. You can set the charge current of the BQ24640, however this part does not have Dynamic Path Management, and cannot regulate input current to BQ24640 (output from USB). From your application, the charge current is low, and as this part was designed for higher currents, the accuracy for charge current will not be ideal, resulting in fluctuating input currents. For example in the d.s at 1.5mV differential voltage, charge current accuracy is +/- 50% and from your description of USB input source, it probably won't be able to supply this current, causing VBUS to sag and hitting the undervoltage lockout of BQ24640.

    Unfortunately for such low current, we do not have charger IC to support your application. I am able to support charger questions, however if you have questions about your application regarding other specific parts, you can direct your question to the relevant E2E forum, and an expert regarding those parts can answer your questions.
  • 0 in reply to Kedar Manishankar
    Prodigy 100 points
    Would you please recommend an E2E forum that is relevant to my issue?
  • 0 in reply to Kitong-H
    TI__Mastermind 24075 points
    Hi Kitong,
    I am not too sure about which part would work, but I would direct you to TI.com, where you can use the parametric search tool for identifying which part would best fit your application. Product folders will have collateral and documents that can assist you in designing your system, and from there you can use the specific part and post to the E2E forum, and it will be directed to the appropriate TI expert engineer, who can answer your question.