TLC59711: Current consumption when not in use

Hi Nir,

There is no shutdown pin on TLC59711. You can set the 'BLANK' bit to '1' to force off all constant-current outputs. You can find the supply current when BLANK = 1 from the 'ELECTRICAL CHARACTERISTICS' section on the datasheet. (A screenshot is shown below.) 

Since your system is battery powered, I think we may have some better choices for you. For example, you can check LP586x series which has an ultra-low power consumption Icc <= 1uA in shutdown mode. 

Could you please provide more detailed information so that I can make a better recommendation for you? For example,

1. What is your application? What lighting effects do you want to achieve with our device?

2. How many LEDs are you going to drive? How many LEDs are in series / parallel? What's the current requirement?

3. What are the available power rails?

Best Regards,

Steven

Hey Steven,

Thank you for your detailed answer. I'll try an answer all of your questions and explain further:

Our system, which is a special display device, is comprised of 3 boards. Each board has 192 white leds, each led brightness should be controlled individually using a 16 bit PWM signal to a total of 576 leds. To make things more complicated, each led can draw up to 0.4W of power. Usually not more than 100 leds will light up at once. No leds are connected in series or in parallel. The power rail is arriving from a 10.4V battery but that power rail, while charging, can reach a voltage of 17V.

When I began looking at your display controllers, I did want to use the LP586x series but soon realized they did not have the needed current drive I was looking for. I then turned to the TLC59711 device since instead of going up in the current, it offered the possibility of increasing the voltage (up to 17 volts as compared to the 5.5V VLED on the LP586x) so for example I could use 6V leds instead of 3V leds. Using 6V leds with a current of up to 60mA per channel (led), gave me 0.36W of power which is good enough.

Using the TLC59711, I will require (576/12) 48 devices. Even if I set the  'BLANK' bit in all of them, teh system will still consume (2mA * 48) ~ 100mA which 

is a lot!

One idea I had was to stick with the TLC59711 based design and control the power going into the VCC pin of all the 48 devices - just shut it down

when there is no need for any display.

I would love to hear your mind on all of this.

Thank you,

Nir.

Hi Nir,

Thanks for replying. Below is a summarized list of your requirements. Please make a correction or supplement if I misunderstand or miss something.

• Number of LEDs per board: 192
• Scan or direct drive: direct drive
• Dimming method: 16-bit individual PWM dimming
• LED current / voltage: 60mA / 6V
• LED voltage rail: 10.4V ~ 17V

Below are some comments:

Nir Dvash1 said:

The power rail is arriving from a 10.4V battery but that power rail, while charging, can reach a voltage of 17V.

1. Directly driving LEDs with TLC59711 in such a case won't work: 
   1. Nearly half or even larger than half of the power is wasted on the current sinks. This is unacceptable if your system is a power-critical case, like a battery-powered system.
   2. An extreme case is that when you turn on all 12 channels at full 60mA at power rail = 17V, then the power dissipation at the chip is going to be 12 * 60mA * (17V - 6V) = 7.92W. TLC59711 cannot withstand such big power dissipation (You can refer to ABSOLUTE MAXIMUM RATINGS and THERMAL INFORMATION from the datasheet). You can add resistor in series with LED to share power dissipation. But it only helps with protecting the chip, not improving the power efficiency. 
2. LP586x does not fit your application.
3. A better solution coming to my mind is using a BUCK converter to step down the voltage before it is supplied to LEDs. 
• Nir Dvash1 said:

  One idea I had was to stick with the TLC59711 based design and control the power going into the VCC pin of all the 48 devices - just shut it down

  when there is no need for any display.

Having a power switch may help, but you should also take into consideration the power dissipation on that power switch.

4. If you plan to step down the LED voltage rail, then you can check TLC5948A, which has a power-save mode to minimize VCC current.

Best Regards,

Steven

Hey Steven,

Oh sure - I did not mention it but the power rail will be fed to a buck converter that will lower the voltage down to about 6.5 volts. That DC/DC will have an enable pin which I would use to turn that power on/off.

Nir.