LM3643: Simulation using Pspice for TI

hi Kelly

Would you mind sharing the waveform of inductor? and how you set the current limit related register shown below?

Mason,

ICL is configured to be 2.8A. Please see attached schematic.  I set run time to 20ms, then I see LED current rise to 700mA. Before I set it to 10ms. Yet, the current rise time is super long, please see attached simulation result. But the falling time is much shorter compared with the rising time. LED current at its set current value of 700mA only for 1.3ms although strobe duty is s16ms. Is it normal or the trans model parameter is not properly configured? When I look at the data sheet, it is very different. IR mode waveform in data sheet is attached also. Thank you for your help. 

hi kelly

what is the forward voltage of LED? now the input voltage is 5V, based on my understanding, normally, Vf=3V, then buck converter is needed rather than boost.

Since I have not found a LED Pspice model that I can edit, I use the one comes together with the TI simulation sample. Considering most LED is of VF from 2.8V to 3.4V, I agree that LM3643 works in pass mode not boost mode. Waveform shows in pass mode, response is even better. 

hi kelly

yes, this mode is specially for better response speed in some IR applications. Would you mind sharing your application here for LM3643?

Mason,

Thank you for your reply.  Our application is the same as in the simulation schematic. It is not exactly IR application since the LED it drives is not IR LED. It is a white LED. 

hi kelly

thanks for the information. BTW, is this device used for phone camera

It is not for phone camera. It is for scanner.

Mason, do you have any update on the simulation result of the delay in IR mode? Thanks. 

hi Kelly

pls allow me some time to download this model and see how it works. thanks

hi kelly

Pls follow below configuration. 

to better the performance of LM3643, recommend to apply for one EVM

meanwhile, would you mind sharing what application is for LM3643 

Thank you for your reply.  It is used to drive a large power LED which is rated 1.5A. The exact schematic is as picture.  

 It is trying to control the LED on time by duty of strobe signal.  LED1 in set to current 1.4A, LED2 is set to not in use.  But when Strobe signal pulsing, OVP error shows. Simulation is performed to see its output voltage levels.   I revised the simulation to turn on only LED1. It is the like the following,  

Simulation results is as above. Somehow, no output voltage beyond 5V is observed according to the simulation result.  Is it because continuous strobe driving it? If it is, what is the maximum driving current in continuous flash mode? 

hi Kelly

min. threshold of OVP is 4.86V. From waveform, it is possible to trigger.

Mason,

Does it mean LM3643 actually can't be use with 5VDC input? When I change source V14 from 3.6V to 5V, the Vout is always goes up to 5V which is always beyond the minimum OVP threshold 4.86V.  Can you let me know how to configure LM3643 simulation model so that it can be used with 5VDC power supply?  LM3643 data sheet says its input can be from 2.5V to 5.5V. 

Thank you. 

Mason,

Do you have further information on the OVP spec and how to avoid it?

Thanks,

hi Kelly

From the simulation result at my side, the output voltage will reach OVP point when input is in the range of 5V-5.5V, but as this is recovered fault, I do not see big impact on dimming current from simulation.