Welcome to the LED Drivers/LCD Bias Section of the TI E2E Support Community. Ask questions, share knowledge, explore ideas, and help solve problems with fellow engineers. To post a question, click on the forum tab then "New Post".
Q: TLC5940 - Current Limitation by 1140759
We inherited a design from another company which uses the TLC5940 to drive a set of infrared LEDs at high-current. The VCC they are applying to the LEDs and the 5940 chip is 3.6V.
We are setting the current using a 332 ohm resistor on pin 27 (IREF), which should give us approximately 120mA of output current per channel. However, the datasheet states that operating the part at less than 3.6V limits our maximum current to 60mA. Could the part be damaged by this configuration?
If not, where does the 60mA limit come from? Is it possible to drive some of the channels at the full 120mA despite the lower VCC? If so, how many?
A: Re: TLC5940 - Current Limitation by 10449
Powering the TLC5940 with less than 3.6V and trying to sink 120mA will not damage the IC. The 60mA limitation exists becasuse 3.6V input voltage is not enough voltage to fully turn on the internal FETs to sink 120mA. Although some TLC5940 IC may have outputs that can sink 120mA with Vcc=3.6V, this functionality is not specified to work and may not be repeatable from IC to IC. Note that you can connect TLC5940 outputs in parallel. With Vin=3.6V, you can change RIREF to set each output to 60mA and then connect two outputs in parallel to drive a single LED at 120mA.
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.