Need IC recommendation - OLED Light Panel (Vf=8.5V @ 0.75A) from 3.7V LION

Hi Sadry,

You may want to try LM3410.

Best Regards,

Issac.

Hi Issac,

I actually use the LM3410 in a lower powered OLED application (~250mA @ vf=8.5V).  However, I wonder if the switcher can support  0.75A of current. It will have almost 6.5W thru it!

Why the TI Workench does not show it as a solution when I choose a custom LED with vf=8.5V and 0.75A of current and power source of 3-4.2V (Lithium Polymer) battery?

Sadry

Hi Sadry,

With a worst case calculation, I assume the input voltage at 3 V and the max output voltage at 8.5 V.

The boost conversion ratio is at 2.83.

Assuming further that the efficiency only at 83%, the boost conversion ratio will be at 2.83 / 0.83 = 3.41.

Your target application is running at 0.75 A, therefore, the average current flowing through the NMOS inside LM3410 will be at most 3.41 x 0.75 = 2.56 A.

LM3410 can support max 2.8 A peak current.

I believe it is feasible for using LM3410 if inductor and switching frequency are chosen carefully.

Best Regards,

Issac.

Hi Issac,

Thanks for the analysis.  I would like to have some margin on the design if possible since the OLED intensity may have to be adjusted by pumping more current thru it than 0.75A and that will also increase the Vf to ~8.9V.

Two questions

1) How do I select the regulator switching frequency and inductor for the case you provided analysis for? The TI Workbench simulator does not provide this information for these parameters even when I choose a "custom" LED.  Is there a way to get the workbench provide information for a given product (i.e. LM3410) instead of by application type?

2) What other part will be able to do what I need some I can assume 1A of current and vf=8.9V?  

FYI, I need dimming control as well (PWM DIM is preferred).  With LM3410, I have noticed that the DIM pin can impact the noise on VIN significantly when the switcher is turned off and on with DIM.  That has created issues with my CPU resetting due to VCC dips and I had to play a lot with DIM frequency and output capacitance, etc. to get it working correctly.  Low ESR input bulk capacitance did not help with this.

Best,

Sadry

Hi Sadry,

I looked through Webench and now I know why it does not list LM3410 as an option.

The minimum current limit listed on the datasheet is 2.1 A.

That's why with 8.5 V / 0.75 A application, it is not suggested as the current flowing into the MOSFET inside would be exceeding 2.1 A.

I'm sorry that I'm not able to suggest any products within the Lighting Power Products product line for your purpose.

However, I suggest you seek for other products from other product line (such as TPS611xx) for possible answer.

Thank you very much and sorry for making a not suitable suggestion!

Best Regards,

Issac.

Thanks Issac for your prompt response on this.  I will look into TPS611xx

Sadry