Viper26LN 400V to 24V

[MNeun.1]

Hello,

I'am currently working on a implemented design out of the DesignStudio. The general purpose of the Viper26 in Buck Config is to supply another DCDC with 24V. Currently a load of 110 Ohm (Bleeder) Resistor is placed for testing purposes which results in a avg. I of around 180 mA. (peak at around 225mA) with 4400 µH Inductor.

Now the question: The circuitry works as expected up to about 180V. After this the circuit shuts down. I have tried several things including: reducing output voltage to 18V (overvoltage Vdd?), higher inductor values (lower ripple current), thermal measurement (case temp 40 °C) , changing comp network etc. The ton time at 170 V is still 3µs so no minimal ton time...

What could be the reason for this shutdown?

Thanks a lot in advance and all the best

Matthias Neuner

[Peter BENSCH]

Welcome, @Matthias Neuner​, to the community!

The VIPER26LN is not suitable for a 400V buck. the eDesignSuite also prohibits this when trying to specify a voltage higher than 300V.

Instead, you could consider the VIPER267K, with which this is feasible.

Also, your buck inductance seems to be significantly too large. With a quick check, I currently come up with 10% of your current value, which is about 400µH.

Hope that helps?

Regards

/Peter

[MNeun.1]

Dear Peter,

thanks for the clarification.

Okay because the option was selectable inside the eDesigner, which was probably some bug than (see picture below). By the way the VIPER are really powerful! 🙂

Nevertheless the VIPER267K is only available with the SO-16 package. Is there something available with the PDIP 7 package and equal pin-out than the VIPER26LN which can handle this conditions?

Thanks a lot and best regards

Matthias

[MNeun.1]

Hi Peter,

just to be clear: Input is 400V DC not AC! I am simply not using the rectifier at the input.

[Peter BENSCH]

The VIPER26K is indeed not available in DIP.

But with the screenshot, the requirements are a little clearer and the VIPER26LN should work for your application - if the conditions fit.

If I understand you correctly, everything works down to approx. 180VDC, right?

What voltage range would you want to cover?

[MNeun.1]

Okay, maybe for the next design I'm using this one.

It works up to 180VDC yes, depending on the conditions. Maximum i reached was about 220V DC with lower load of some mA.

I would like to use it in a inverter application with 100S battery pack => around 300-400VDC. I expect a max. DC current of about 300mA. If this is too much I coud go a little bit higher with the Output Voltage, max up to 30V (For sure than a resistor connected to the VDD is required to limit this). As you have mentioned the smaller inductance, is it better for the VIPER to be used in DCM?

[MNeun.1]

Hello,

maybe to clear up things a little more. The first image (scope_1) is done with 204VDC, 214 Ohm of bleeder resistance + some other circuitry, 470 µH and 47µF cap. This results in a avg. current of 100mA. Switching f is 63 kHz and clearly in DCM. ton time around 850 ns. If I increase the voltage to 207 it will stop.

The second image (scope_0) was done also using 470µH and 47µF cap (50V) with a VDC of 206 volt. Here the burst mode is active as the avg. I is only 20mA.

After this (around 207VDC) the circuit tries to restart . I can't identify the reason for this as no overcurrent is given and no minimum ton time is reached...

Just to be sure that I have a original product: The package text is: CHN VIPER26L F52207.

Do you have any ideas? Thanks a lot!

 

[Peter BENSCH]

In order to recognise a component as a fake, at least the Bulk ID is required, which can be found on the sticker of the packaging. If you have it, you should keep it confidential and only give it to us via PM and as a photo for verification, because otherwise it can be misused.

However, I do not suspect a fake component, but other reasons. You are not yet at the min on-time, but you are getting closer and closer to it as the input voltage increases, whereby the parameters of the surrounding devices become increasingly noticeable: especially the layout should be mentioned here, but also the parameters of the buck coil, for example.

If you have a contact, e.g. the FAE of a local distributor, you should take a look at your setup together with him to narrow down the problem.