Recommendations please – I2C or SPI controlled 2 channel 12 bit PWM driver

• Recommendations please – I2C or SPI controlled 2 channel 12 bit PWM driver
  Posted by Mr.B on 30 Jun, 2014 04:20
• Hi all,
  
  I don’t know if this is the appropriate place to post this…
  
  I have recently been working with the NXP PCA9685, an I2C controlled 16 channel 12 bit PWM driver.
  They are relatively cheap and easy to implement.
  
  A design I am currently working on requires only 2 channels and the board needs to be fairly small. The PCA9685 is a bit of overkill with its 16 channels, and a bit physically large (TSSOP-28).
  Can anyone recommend an I2C controlled 2 channel 12 bit (or more) PWM driver in a small SMD package?
  I have hunted through Mouser search and cannot find anything suitable.
  
  The device will be controlled by an ATmega328p-au, so the comms to the PWM chip can be either I2C or SPI.
  
  Background to the design: ATmega328p-au, nRF24L01 radio, PWM driver, Power MOSFET x 2.
  Forms the basis for a receiver module for dimmer control of 12vdc LED strip.
  Transmitter/Controller yet to be designed.
  
  Thanks in advance for any help.
  
• #1 Reply
  Posted by Kremmen on 30 Jun, 2014 04:43
• Any reason why you can't do it directly from the MCU? The 328 has 6 pwm channels built in.
• #2 Reply
  Posted by Mr.B on 30 Jun, 2014 04:56
• They are only 8 bit.
  The first 20 or so steps of fade up look terrible.
  Particularly if you are doing a slow fade - 0 to 100% over 10 seconds.
  
  Thanks for your response anyway.
  
• #3 Reply
  Posted by PedroDaGr8 on 30 Jun, 2014 05:14
• Quote from: Mr.B on 30 Jun, 2014 04:56

  They are only 8 bit.
  The first 20 or so steps of fade up look terrible.
  Particularly if you are doing a slow fade - 0 to 100% over 10 seconds.
  
  Thanks for your response anyway.
  

  
  What about the TLC5973. I just saw it mentioned in another thread.
• #4 Reply
  Posted by Mr.B on 30 Jun, 2014 05:28
• Thanks for that.
  I will have a good look through the data sheet tonight.
  
  Cheers
• #5 Reply
  Posted by Kjelt on 30 Jun, 2014 08:32
• In the same family there are also serial controlled devices (the TLC5973 is one wire protocol) like the TLC5970 which besides the 12 bit PWM has an additional 8 bit analog dimming.
  Edit: The package of the TLC5970 does not meet your requirements 
• #6 Reply
  Posted by Jeroen3 on 30 Jun, 2014 09:45
• Quote

  "One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
  Mode"

  Whats wrong with timer/counter 2?
  
  And you need a log function pwm to get linear brightness for your eyes.
• #7 Reply
  Posted by Kjelt on 30 Jun, 2014 09:48
• or a LUT a bit more costly but fast and precise.
• #8 Reply
  Posted by miceuz on 30 Jun, 2014 10:24
• What if you just slap in another micro that has two PWM channels on 16bit timer? I guess you can find a lot sot23-6 packaged micros from Microchip or Atmel to do that.
  
  PCA9685 is an interesting part though, shame didn't stumble on it a while ago when I was looking for something like that, almost was going to do my own CPLD solution for that, luckily, the project didn't fly.
  
  
• #9 Reply
  Posted by Jeroen3 on 30 Jun, 2014 12:26
• Great idea, keep rising the bill of material costs. 
• #10 Reply
  Posted by katzohki on 30 Jun, 2014 16:29
• This is an app note from Micro, but the concept applies to any micro you would want to use. Might give you inspiration?
  
  http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en560120
• #11 Reply
  Posted by filip_cro on 30 Jun, 2014 18:46
• You can use 2 channel PWM on OCR1A and OCR1B.
• #12 Reply
  Posted by Mr.B on 30 Jun, 2014 20:26
• Many thanks for all your input.
  It looks to me like the TLC5973 will do the job nicely.
  
  @katzohki
  Thanks for the link. I will need to upskill myself on micros a bit more before I was to jump in to that.
  However, the effort would be well worth it.
• #13 Reply
  Posted by Mr.B on 02 Jul, 2014 04:46
• Quote from: filip_cro on 30 Jun, 2014 18:46

  You can use 2 channel PWM on OCR1A and OCR1B.
  

  
  Thanks for that suggestion.
  After a bit more research it appears that I should be able to implement it within the MCU.
  http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM
  
  I haven't read the full article yet... Looks like Saturday will be spent working through this.