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TPS40210 Not Boosted, help

Qing Zhou1
Prodigy 30 points
Other Parts Discussed in Thread: TPS40210EVM

Hi

I try to use TPS40210 for our boost power supply design. I got a boost converter designed using Webench w/ device TPS40210 for 24V to 180V @ 0.04A boost converter. The schematic is attached. The only thing we changed from the schematic is we using 0.1uF/250V on Cout instead of 105uF.

The output voltage is not boosted to DC180V but DC23.5V (input - diode drop). On checking the frequency at RC (pin 1) is found to be about 330Khz and Voltage at BP (pin 9) is 8.14 V but no voltage at GDRV (pin 8).

1. Can the change of Cout cause this?

2. I use 24V DC switching power supply as the Vin, will it cause this?

3. When I make the GDVR open, it reads 7.85Volts. Otherwise it keeps 0V even I varied the resistant Rg from 4.87Ohm to 200Ohms, 2K and even 220Kohms.

4. I connected all the Ground point together with the Power Pad, will it cause this?

5. Do you have any evaluation board on this output range I can place order?

I appreciate with your help.

Regards,

Qing

 

  • 0
    TI__Mastermind 35115 points

    Qing, please see my comments below. Hope this helps get you in the right direction.

    1. Can the change of Cout cause this?

    I would expect there to still be some switching on the GDRV signal even with the change in Cout. However I still recommend using the values selected by WEBENCH because the compensation is selected for these values. However, WEBENCH's selection might not be the best for the high output voltage with such a low current. It targets CCM operation while this type application could be better off operating DCM. This helps by reducing the inductor size and avoiding any issue due to minimum off-time.

    2. I use 24V DC switching power supply as the Vin, will it cause this?

    This should not cause any issues.

    3. When I make the GDVR open, it reads 7.85Volts. Otherwise it keeps 0V even I varied the resistant Rg from 4.87Ohm to 200Ohms, 2K and even 220Kohms.

    I do not recommend using such large values on the GDRV signal. The small resistance is there to reduce the average current for turning on the FET. Large resistors will reduce the current so much that the FET won't be able to turn on.

    4. I connected all the Ground point together with the Power Pad, will it cause this?

    I'm not sure what you mean, is there a layout you could show?

    5. Do you have any evaluation board on this output range I can place order?

    We don't have one for this output range but the standard TPS40210EVM could be modified to do this. This could help to rule out any layout issues.

  • 0 in reply to Anthony F
    Prodigy 30 points

    Hi Anthony

    Thanks a lot for your answers.

    I ordered the TPS40210EVM and received today.

    Now, I'm going to test the function on the TPS40210EVM.

    Can you please to tell me how can I modify the EVM to get 180VDC output? Can I just use the former design we got from Webench, or we can do something else?

    Appreciate.

     

    Qing Zhou 10/30/2013

  • 0 in reply to Qing Zhou1
    TI__Mastermind 35115 points

    The former design should work well as a starting point. Follow it as close as possible for best results.

    If you have issues, some things to try are:

    1. Lower the switching frequency to increase the maximum duty cycle. The maximum duty cycle is limited by the minimum off time of the GDRV signal.
    2. Reduce the inductance to operate in DCM mode instead. 
    3. The combination of reducing the switching frequency and inductance leads to higher peak currents in the inductor. This could cause the hiccup over current protection (OCP) to be triggered. If hiccup is an issue, the Rsense resistor should be decreased to increase the OCP threshold.