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LM5175EVM-HP: Battery Charger based off LM5175EVM-Hp

Part Number: LM5175EVM-HP

Hello I am attempting to make a battery charger based off the TI LM5175EVM-HP board. I am attempting to use this so I can charge a 12V lead acid battery off a variable input. My power source is going to be variable but capable of approximately 4V - 16V. need to be able to charge the battery at up to 20A. 

I have already changed the board so it has a higher switching frequency ( about 300 kHz), lowered UVLO ( set to 4V now), changed my output voltage ( set to 13.8V), and changed the sense resistors to be able to accommodate the higher currents. So far everything is working ok when I am supplying a voltage on the top half of my range but it isn't working correctly at the low end. 

Any suggestions on how to make this work? I think the issues at the low end are related to VCC maybe being to low for the mosfets.

Is there a different mosfet you know of i could replace these with to help?

Is it possible to supply the power to turn on the fets from the battery i would be charging since even when it is drained it will have a pretty high voltage and then use the incoming power from supply to still charge the battery? Sorry just throwing out ideas.

Any help is appreciated


  • I don't think the MOSFETs on the EVM causes such problem. But as your operating voltage is low, you may be able to use lower voltage rated MOSFETs than those on the EVMs, for better efficiency (smaller RdsON and gate charge). You are correct that the device requires adequate bias to operate properly. Yes you can feed your battery voltage to the BIAS pin.
  • Thanks for the response. i think i have managed to solve this part of my issue but now have another question. I am trying to use the Average Current limiting feature of this to basically limit my output current when my input power is not sufficient to maintain the proper output power. Basically i want to use in a constant current mode but be able to adjust what the current limit for the constant current mode is based off my input voltage.

    Any suggestions?

    Maybe you could explain better what determines the constant current mode limit and how to adjust it.

  • In your case, you may consider to use the average current limit feature to limit your input current, as you input capability is limited.

    Either the output current or input current can be limited. When the current passing through the sense resistor exceeds the internal prefixed threshold (50mV), it starts to discharge the SS capacitor, which pulls down the COMP pin and reduces the duty cycle until the current reaches an equilibrium at 50mV.

    Hope this clarifies.