LM3550: BAL pin vs no or single supercap

Hi Fred,
If you don't have the supercap, just leave this pin float, you should not connect a single supercap to this pin, because this pin was used to balance two supercaps.
Sean

Hi Sean,

I did not intend to connect a single supercap to the BAL pin and won't do it.

I asked what to do with BAL pin if using a single supercap (connected to Vout...)

I would connect a single supercap to Vout and leave BAL floating. Will it impact in any way the charge control or the part behavior?

Thanks

Hi Fred,

    Why you consider to put a supercap to the Vout, In most application, put a 2.2uF ceramic capacitor to the Vout is ok.

Sean

Are you serious or just looking at the wrong IC?

The datasheet title is "LM3550 5-A Super-Capacitor Flash LED Driver" and you ask me why I need a supercap?

Try doing the maths to flash at 5A during 50ms with a 2.2uF alone and let me know how it goes.

Meanwhile, I'll assume putting a supercap on Vout and leaving BAL open will work.

Case close until it blows.

Hi Fred,

     I'm sorry that I have misunderstand your meaning. Could you tell me your output voltage? How many leds on the output? And what's your maximum voltage rating of your supercap?

You need output 5A for 50ms? what's your input voltage? Thanks.

Best Regards

Sean

Hi Sean,

Input voltage: 3 to 3.6V

3 LEDS parallel

The output current pattern could also be around 9A for 20ms (once per second).  The exact numbers have yet to be determined.

Considering setting the charge voltage to 5V or 5.3V.

AVX and Illinois Capacitors have supercap series of 5.5V or more without any "center tap".  We are interested in using them.  Hence my question about the BAL pin...

Thanks

Frederic

Hi Fred,
To be honest, we don't have the experience about driving output 9A with LM3550. But it seems ok to drive 9A for 20ms with 1Hz. I suggest to make a simple demo to verify this application. And please tell me the text results.
Sean

9A is a lot of current but using the right FET and sense resistor should make it work.
Talking FET, what's the drive characteristics for the FET_CON pin?

Hi Fred,

    Because this is an old device and I don't find many reference technical materials. You can refer to http://www.ti.com/tool/TIDA-00376 for some reference. Thanks.

Sean

Hi Fred,
I'm sorry that for your application. The answer now is that you can leave BAL pin alone and use one super-cap alone. When you have tested the result , you can reply to this.
I prefer to close this first, when you have the result, we can open this again? How do you think about this? Thanks.
Best regards
Sean