Is there a way to switch the TLC59108 chip into a truly low power mode? I have a board with 3 of these chips driving some surface mount LEDs. On power down I turn off all LED driver outputs and disable the oscillator by changing the MODE1 register but the chips still continue to draw 6 to 8mA each. Alternately is there a more suitable chip I should be using in a battery powered application or do I need to resort to switching the VCC line using a MOSFET.
The data sheet mentions a SLEEP bit on page 17 which I presume should be OSC but maybe I am reading this wrong.
You are correct, on page 17 there should be OSC written instead of SLEEP in the note.
If you would share some of your requirements, we will check if this part is the best fit for you. As far as I understand above, you are driving 24 LED strings. What are your requirements for driving the LEDs? Do you need I2C or could you use another interface as well?
I am designing a small LiPo battery powered device. It uses an ARM controller with I2C and SPI bus and switches to low power mode when not in active use. The device has a string of 10 dual colour LEDs arranged in a bar graph and 4 other LEDs to indicate status. I need a driver for these 24 LEDs that has PWM control for each LED. The current design uses 3 TLC59108 ICs and works well except for the quiescent current when the device is off. I2C is not essential but the SPI bus on the device is currently shared between SRAM, flash and an audio DAC all runnning at 20MHz. The I2C bus is a good fit for controlling the LEDs in this application. Any suggestion for an alternative LED driver would be appreciated.
Rather than an alternative LED driver, you may want to consider adding a load switch to the input voltage for your 3 TLC59108 ICs. I have just tested the TPS22911EVM for this purpose with the TLC59116EVM-360 (in development) and it seemed to work fine. When the TPS22911 load switch was on, and the three TLC59116 LED drivers were running, the ICs were pulling about 68mA of current. The load switch was turned off and that number was reduced to 0.2uA with the LED voltage still active but the LEDs off. When repowering the ICs, the system worked fine. The same results were obtained when the IC power was turned off and on with the load switch staying on.
Although the load switch used above was the TPS22911, it is still in development. You may want to consider the TPS22929. It has an active high QOD and has a leaded package available. Also, it will be able to handle the maximum 5.5V that your LED drivers would be powered by and can handle the maximum amount of quiescent current they would deliver. Other possible options are the TPS22913 and TPS22910.
Load switches are very popular in mobile battery powered applications. If you would like to know more about them, do not hesitate to ask.
The load switch is a good suggestion which I will look into further. I am testing a modification to the current system feeding VCC to these chips from a switch 3.3V source from another part of the board. It seems to work. The chips have their I2C address set via the A0 - A3 pins. Should the ones that pull up to VCC also be switched to prevent possible latchup? I also need to do some testing to check that the I2C bus still functions if these 3 devices are off.
I would recommend tying the VCC from your chips to the address pins (A0-A3) which you have set high. Also, there should not be any problems if the I2C bus is still powered on while the ICs are turned off.
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