LM25037 Modified Square Wave Inverter

Hello

The LM25037 could work as an inverter provided that ...

     An external error amplifier is used to generate the control signal for the LM25037. This external amplifier would have to have to compare the actual output voltage to a reference signal.

Whether or not you need gate drivers depends on the topology you choose. If you use a push pull topology with a centre tapped transformer primary, like that shown in the datasheet, then you won't need gate drivers - although you may still choose use them for other reasons, dissipation, physical layout for example. If you choose a half bridge topology then you will. Remember too, that driving the MOSFETS directly from the OUTA and OUTB pins will increase the dissipation in the controller - using an external gate driver reduces dissipation in the controller.

 The 75V maximum voltage at the VIN pin is respected as is the total chip dissipation limits.

I'm not sure what your application is so some questions

What do you mean by 'Modified Square Wave Inverter' - is the output a square wave or trapezoidal or stepped in some way?

What is Freq_mod? is this the output frequency?

Is the input 300VDC? - what is the expected range of operation - min/max?

What is the power level? - this would feed into choice of topology.

Regards
Colin

Hi Colin-san

I appreciate your support.

I answer your questions below.

1.What do you mean by 'Modified Square Wave Inverter' - is the output a square wave or trapezoidal or stepped in some way?

    -> "Modified Square Wave Inverter" means that it is DC-AC converter and the output is AC that it is not an accurate SIN wave, it is quasi-sine wave (modified Square wave) 

    -> Please refer to UCC28089 datasheet. (P.11)

      http://www.ti.com/lit/ds/slus623a/slus623a.pdf

2. What is Freq_mod? is this the output frequency?

    -> Yes, it is the output frequency.

3.Is the input 300VDC? - what is the expected range of operation - min/max?

    ->  The input  voltage is 300Vdc. But min/max is not decided exactly yet.

4.What is the power level? - this would feed into choice of topology.

     ->  The output power is 100W.

5.The application is car equipment like below.

      http://car-inverter-review.toptenreviews.com/whistler-pro-200w-details.html

The customer would like to use LM25037 for above application.

Could you give us any advice about LM25037 if it is possible.

Regards,

Koji Hamamoto.

Hello Koji

Thanks for the extra information, things are a lot clearer to me now.

I assume that the system input is 12Vdc which is converted to a regulated 300Vdc by a flyback or other isolated stage. That means that the inversion function becomes very simple in concept - essentially the circuit shown in the UCC28089 data sheet - thanks for pointing this out to me. So the inverter runs at a low frequency (55Hz for example). The minimum oscillator frequency of the LM25037 is not going to be less than about 20kHz, which is a long way from the 55Hz you are looking to reach. I think this eliminates the LM25037 from consideration. Why not use the UCC28089? - the application drawing shows a 145V input bus, but there is no reason why it couldn't run off a 300V bus.

Regards
Colin.

Hi Colin-san

Thank you for quickly reply.

Your assumption is correct.　The whole power flow of this application looks like the following.

  12Vdc -- ( Isolated DCDC: push-pull ) -- 300Vdc -- ( DCAC ) -- 220Vac

Regarding the frequency, I understood that it is difficult going in LM25037.

>Why not use the UCC28089?

   Because UCC28089 is not for Automotive (means Q1).

Regards,

Koji Hamamoto.

Hi Colin-san

Would you please give us any information if there is a device that you recommend to this application.

(I would like to automotive products.)

I appreciate your great support.

Regards,

Koji Hamamoto

Hello Koji-san

The best thing to do would be to post this query in the automotive forum at http://e2e.ti.com/support/applications/automotive/f/26.aspx because it will then be directed to people who are more familiar with the automotive product line.

Having said that - does the product really need to be automotive rated. The Whistler application you mentioned earlier is clearly an aftermarket device, not an embedded device so it can be suggested that a commercial device is suitable. Of course, if the application is an embedded one, then an Automotive rated part may be necessary.

Another idea would be to use the switching circuit shown in the UCC28089 datasheet and use a really simple state machine to drive the MOSFETs - for example a simple 555 timer with some basic dividers and steering logic - although I didn't see an automotive rated 555 in our product offering. How about using an automotive rated microcontroller such as the MSP430F2013-EP. This device would allow some additional functionality too - current limiting, over temp protection and so on. It would also be possible to use it to control the input stage flyback too - although it might be simpler to use two separate controllers.

As I said, the best way forward for you would be to re-post in the automotive forum but I hope that my suggestions above give you some food for thought.

Regards
Colin