TLC5925, Very low requested current (~1mA) with regard to the setting (15mA or 50mA)

Pascal,

The datasheet shows the current range for the TLC5925 as 3mA to 45mA.  We have fully characterized over that range.  We have taken lab data below 1mA.  The driver continues to work, but the accuracy is not necessarily within the same range.  

If you are looking at levels below 3mA, our lab data suggests there will be no issues.  But, we do not test or specify the driver in this range.  I suggest you evaluate the device under your specific requirements to verify our lab results.

Regards,

Dick

Thank you Dick for the answer,

Before to start anything, I look for any contraindication.

Can you confirm if I understood well? If I have a the TLC5925 which have Rext defined to deliver 50mA (or 15mA), but I use only 3mA, I keep the all characteristics of the TLC5925.

Best regards,

Pascal

Pascal,

The TLC5925 is a constant current LED Driver.  What that means is if you set the output current to 15mA, the device will sink 15mA when programmed ON.  You cannot get to only 3mA.  If you need 3mA, you must program the REXT for 3mA.

If you need to change the current outside of changing the REXT,  you may consider the TLC5926.  The TLC5926 features a Current Gain register that allows the device to be programmed to change the output to less than 100% of the programmed output current.  You can program the current with the REXT to be 15mA, then change the Current Gain register for 50% and the result will be 7.5mA per channel.

Pulse Width Modulation (PWM) dimming is also an option.  In this case, you program 15mA, but use the OE signal to operate at 50% duty cycle.  With a fast enough frequency on the OE pin, the LED will appear to be operating at 50% of its programmed brightness.  

Regards,

Dick

Hi Dick,

Many thanks for your follow-up.

Sorry, but I did not say everything. In reality for diverse problems, I am obliged to use a transistor as driver Leds (voltage source). So the current given by the TLC5925 is only for the command of the transistor.

This is the reason, that I use only 3mA among 15mA or 50mA fixed.

I can't change any thing, except the side of Led. And If possible, I wouldn't like to consume twice more.

Best regards,

Pascal

Pascal,

Thank you for the clarification.  So, you are using a resistor divider at the output of the TLC5925 to drive the base of an external transistor.  The output of the driver will pull the signal low and the resistor ration will be set to allow the correct "on" voltage level at the transistor and will pull up when to the supply level when "off".

This method will work.  I understand the need to keep the output low.  I would suggest an experiment to monitor the output voltage as the available current is reduced.  How low will the output pull when current limited?

Regards,

Dick

Hi Dick,

Finally, we shall not use this solution.

But on a corner of table, in high and low temperature the component worked for a current lower than that planned ( 0.5mA ).

Thank you very much for your help.

Best Regards,

Pascal