This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Part Number: LM3409HV
I've been looking at the evaluation kit documentation and the datasheet for the LM3409HV LED driver. The datasheet says that I can connect an external power source between 0-1.243V to limit the current. I was wondering if it is possible to use the IADJ pin to do just this and then also use PWM on the EN pin to limit the final current to the LEDs. For e.g. if my design is set for max LED current of 4A then can I use the IADJ to set this max current to say 3A by varying the VADJ and then use a PWM signal to vary the end output current between 0 to 3A?
Yes, that is a common way to operate the device. You can use any combination of IADJ voltage and EN pin duty cycle to adjust your average LED current.
In reply to Clinton Jensen:
In reply to HPB:
This device is designed to start very quickly which is how you get fast PWM dimming. However if you apply the IADJ voltage through an RC after you have reached your UVLO level it will implement a soft start as the peak current will start low and increase as the cap charges.
Awesome. Is there a way to calculate the soft start time? Rather is it possible to calculate the RC values to match a specific soft start time?
You can approximate it as tss = VIADJ*R*C where VIADJ is the max voltage applied to IADJ. You can get even closer if you want by using a natural log equation for charging a capacitor, but a simple RC time constant will be close.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.