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LM5170EVM-BIDIR: LM5170EVM-BIDIR: Voltage regulation, current control

Tri Cuong Do
Prodigy 20 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170

Dear support member,

Hi, I bought the model LM5170EVM-BIDIR. I want to make it operate as a buck converter. 
Desired operating as below:
Input Voltage: 48V
Output : 12V and charge to battery
The set up is as the attached picture. 

When I close J36 and do not used ISETA, the output voltage is 14.5V. How can I control the output current with this fixed voltage value? I want to charge a 12V battery with different current values. I mean I need a controllable output current but at fixed 12V or 14.5V.

When I open J36 and use ISETA (0 to 1.5V), the output voltage is kept at 20V. It's not possible to use the DC/DC converter to any application.
Can you give me some suggestions for my problem? 

Thank you so much and I am looking forward to your response. 

Best Regards,

  • 0
    TI__Guru 68875 points

    Hi Tri Cuong Do,

    Thank you considering the LM5170. 

    First, you are correct to control the current :  Open J36, and use ISETA.

    However, from your picture, I don't see anything is connected to the 12V port. Basically you have an open circuit there.  If you apply a voltage to ISETA, then the LM5170 tries to produce a load current proportional to the ISETA voltage, but the current has nowhere to go after the output capacitor is charged up.  Then you hit the output OVP (preset at about 20V) and the circuit gets stuck there.

    When you use the LM5170 to control the charging current, you must have the battery connected. You can first try to use an E-load in CV mode, and set the CV level to any value between 0 and 20V (avoid hitting the OVP), then you can freely control the charging current by ISETA.

    If you want to adjust the output OVP, change the resistor at OVPB pin.  Please refer to the datasheet for the selection equation.

    Thanks,

    Youhao Xi, Applications Engineering 

  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hi Youhao Xi, 

    Thank for your reply. 

    I already connected a power resistance 1 ohm and 300W to the 12V port. However, when I used J36, the output voltage is 14,5B and the current is overload. 

    When I used ISETA, the output voltage at 12V port was 20V and we could not adjust the voltage and current. The set up is as the attached picture.

    Can you give me some suggestions for my problem? 

    Thank you so much and I am looking forward to your response. 

    Best Regards,

     

  • 0 in reply to Tri Cuong Do
    TI__Guru 68875 points

    You should not use a resistor as the load to operate with ISETA.  ISETA forces a current proportional to it value.  If  you set ISETA=1.5, you will basically forces 60A (dual phase) to the output, and it would produce 60V across this 1Ohm resistor, well above the OVP threshold of about 20V.  For sure your circuit will get stuck there.

    Like I mentioned, you need to use an E-load at CV mode, and you can adjust your CV voltage level between 0V and 20V, and set you ISETA from 0 to 1.5V, then you can see 0 to 60A current is produces, regardless of the CV voltage level. This is just the expected behavior of current source. 

    If you insist to only test the EVM with your 1Ohm resistor load, you cannot apply a voltage higher than  0.475V at ISETA for dual phase operation, or 0.95V for single phase operation.  Then you can see  your output voltage is proportional to ISETA:  Vout = 1 Ohm x Iout  = 1 Ohm x V(ISETA) x 40, for dual phase.

    Thanks,

    Youhao