LM3643: Transfer efficiency

Went Cao

Genius 5550 points

Part Number: LM3643

Dear all

As below link, it said using the LM3643/4/8 in an Inductorless, I have two questions about this application.

1. What about transfer efficiency in this application ? Is there any conversion efficiency curve ?

2. How long will be output after enable the TORCH/TEMP pin?

http://www.ti.com/lit/an/snva759/snva759.pdf

over 5 years ago

0 Sean Zhou over 5 years ago

TI__Mastermind 22745 points

Hi Went,
1.When it works at pass mode(without the inductor), this a linear transfer system, efficiency equals to Vout/Vin, because the Vout various from the LED specs , there is no detail efficiency curve.
2.For torch mode, the ramp time depends on the how much current that you need. it should be less than 200us.

0 Went Cao over 5 years ago in reply to Sean Zhou

Genius 5550 points

Dear Sean

3. If shut down the LEDs, is there any voltage on LED1 and LED2 pins ?

4. At the pass mode, does it need a big input capacitance on the IN pin ? I had check other design, there is a 330uF input capacitance, what is function of the 330uF capacitance ?

0 Sean Zhou over 5 years ago in reply to Went Cao

TI__Mastermind 22745 points

Hi Went,
3. If it shot down, there is no voltage on LED1/2 pins;
4. Some customer and application has used large input capacitor, 330uF was used to decrase the input volatge drop when you use the battery to power supply the system.

0 Went Cao over 5 years ago in reply to Sean Zhou

Genius 5550 points

Dear Sean

3. What about Vout pin ? Is there any voltage on this pin ?

5. Below MOSFET,can I shut down it ? How to do ?

0 Sean Zhou over 5 years ago in reply to Went Cao

TI__Mastermind 22745 points

Hi Went,
Yes, there is voltage on VOUT pin for fast response. Yes, in pass mode(Vin is larger enough for output), this MOSFET will not turn on, it will keep off.
Regards
Sean

0 Sean Zhou over 5 years ago in reply to Went Cao

TI__Mastermind 22745 points

Hi Went,
Please help me click "Resolve", thanks.
Regards
Sean

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LM3643: Transfer efficiency