PWM IC question

I don;t use it because findchips.com shows no one carrying that part.

If Newark, Furure, Mouser and DigiKey don't carry it, I'm unlikely to use it.

The Dallas datasheet is dated 7/2001 so either it didn't take off, and is due to get discontinued, or ........

Why not just use the PWM output from a micro? 8 or 10 bits instead of

5 and (the micro I'm working on at the moment has 5 of them), which ought to be enough for most purposes. Then there is the M*x*m issue.

Best regards, Spehro Pefhany

The micronctroller's I've used were tied up completely when running a PWM channel, and only offered a couple of them.

I'm envisioning a project that will require simultaneous control of four independent motors, along with a fair number of other activities, and for that, I'm going to take a serious look at a dedicated PWM chip.

Then you probably weren't doing something right. I've made an eight-channel servo controller out of a atmega32. It managed 8 PWM channels, 8 A2D channels, and responded quickly to i2c bus commands without skipping a beat. As long as your chip is fast enough and the interrupts are configured correctly, PWM should never be too much of a load. Only when you need a serious number of channels, in the dozens, should a separate chip be needed.

If you use an atmel 8051F??? with a PCA (programmable counter array) you can use 5 channels PWM without it costing you any cycles.

Good luck,

Peter

Thanks for all of your responses. It all makes sense. I did have a tough time finding these chips too. I ended up ordering them from Dallas/Maxim themselves.

These IC's do cost money too. Where as PWM in a processor would be "free". Just would take a bit of configuration code.

I guess I prefer the ease of use factor. The IC is very small(MSOP-8) an d I have I2C available anyway. I am only using two of these PWM IC's but I can add up to six more later if needed.

I am using a PIC 16F877A processor. While the '877 does have PWM, I felt it would be a better use of the on-chip resources to take the PWM off chip. This way I have full use of all of the IO pins on the processor as well as all of the timers and such. Addtionally, I find the PWM on this part to be too low of a frequency which causes the motors to emit a whining noise.

I will look into the processors you have mentioned. I am interested in trying some different microcontrollers and learning to program them.

Thanks aga> Hi all,

At 20MHz you can get 10 bit resolution with a 19.53kHz PWM frequency. If 8 bits is okay, you can get 78.12kHz, or with a 4MHz clock, 15kHz. You can get 31.26kHz even with a slow 4MHz clock by going down to 7 bits resolution. See the midrange reference manual for details.

At 5.5 bits & 20MHz clock you could do a 200kHz+ PWM!

If you can handle SMT, the PIC18F series has some members with 5 PWM channels and loads of other goodies in an 80 pin TQFP, and not that expensive. They run at 40MHz.

Best regards, Spehro Pefhany

If it means buying a $50 microcontroller instead of a $6 microcontroller, it's not "free".

Many micros have dedicated PWM that is done in hardware. After you configure it for the clock rate, period, etc, you just set your duty cycle value in a register and the hardware does the rest in the background. No processor cycles are consumed handling the PWM at that point. For example, my MAVRIC-II board that uses an Atmel ATmega128 (see the URL in my sig for more info) has 6 of these channels that can be run at pretty high resolution depending on how they are configured. Most of the smaller AVRs have 2 or 3 of these channels. I'm sure PICs have them too, but I'm not so familiar with those.

-Brian