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CSD95490Q5MC: I cant seem to get a useful waveform from the IOUT pin on the CSD95490Q5MC

Dean Yencer
Prodigy 20 points
Part Number: CSD95490Q5MC

I am using the CSD95490Q5MC as a smart controller for a buck circuit in a larger power supply. i am trying to obtain useful information from the IOUT pin and am running into issues. my company has access to the full data sheet but without an example waveform or example circuitry its hard to tell exactly what i should be seeing and how to correctly setup the circuit. i have setup the LOUT pin with 250KΩ resistor as my output inductor is 300nH. TLDR; has anyone had success with the IOUT/ current monitorin circuitry and do you have information as to what i should be seeing on the pin itself/

  • 0
    TI__Expert 3525 points

    Hi Dean,

    Thank you for your interest in CSD95490Q5MC.

    With 300nH inductor, you will need to use the 250k ohm resistor between LSET pin and PGND.

    The IOUT is an output pin, and should be used in pair with REFIN pin. The REFIN pin needs to be connected to an external reference voltage, such as 1.7V.  The differential voltage between IOUT and REFIN is proportional to the sensed current (typically 5mv/A). By monitoring this differential voltage with differential voltage probe or sensing circuit, you can get sensed inductor current information. You may add a 0.1uf/X7R bypass capacitor between REFIN and PGND to filter out noises on the reference voltage, and this bypass cap needs to be as close as possible to REFIN pin if you add it.

    Please note that, the differential voltage signal between IOUT and REFIN is a small signal, so it's suggested to keep it away from any noisy sources. Please let me know if this solves your problems.

    Best,

    Qingquan

  • 0 in reply to Qingquan Tang
    Prodigy 20 points

    Hello Qingquan,

    I have purchased the PS53667EVM-769 evaluation board in an effort to eliminate any variables surrounding board layout, incorrect Lout resistor choice etc. However even with he dedicated CS pins i am still finding it difficult to get anything remotely consistent from the lout pins. the datasheet for the buck controller says the pin represents emulated current on my output inductor, so what i fail to understand is how comparing that to a dc voltage gives me the formula of ref(V)- iout(V)/5(MV/A). perhaps you could tell me specifically in regard to the evaluation board what points to measure across and what i should be looking for in terms of output.

    thank you!

    Dean

  • 0 in reply to Dean Yencer
    TI__Expert 3525 points

    Hi Dean,

    Have you tried to measure voltage between IOUT and REFIN pins with a differential voltage probe? That should give you the signal emulates inductor current. (V_IOUT-V_REFIN)/5mV=I_out (A).

    For example, if you measure the signal for U2 on the EVM, you can measure across C54 (cap may not be populated, but it's OK, you can measure across the solder pads), you should get emulated current signal.

    If you still have difficulty, please send me the waveforms you measured to my email: q-tang1@ti.com.

    Best,

    Qingquan