Integrated PWM IC?  (for Class D audio) - Page 1
Forum section: electronics / projects

author: me_engineer
author_rank: Contributor
timestamp: October 11, 2019, 08:14:08 pm
content: Is there an integrated PWM chip available out there, something that contains a clean triangle wave generator and comparator? Ideally I feed it a square wave, and an audio signal, and it spits out a PWM with high fidelity/accuracy. 1-2 channels.There are lots of modulator chips available, but they all seem to require use of their own oscillators and have other restrictions.

author: Boscoe
author_rank: Frequent Contributor
timestamp: October 12, 2019, 06:07:29 pm
content: The LTC6992 is perhaps what you’re after.FYI. If you’re looking to build a class D amplifier you’re best off just using one of the offerings from TI. You’ll never get any where near the performance of the TI solutions without feedback, using feedback in these systems is a nightmare. If you want to build a class d amplifier simply with a PWM generator and a half Bridge it’ll be rubbish.

author: me_engineer
author_rank: Contributor
timestamp: October 14, 2019, 12:38:00 pm
content: Thanks, you are correct that would normally be the case, this is a special use case for some instrumentation. Open loop is fine.The LTC6992 is a nice chip but it looks like it has to use its own oscillator, set by Rset; I'm looking for something that can sync with an external clock (i.e. feed my own square wave).

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 14, 2019, 02:50:18 pm
content: What are you going to do with the output? Do you need a full class-D amplifier in the end? If so, I second the idea of using an integrated class D amplifier instead of rolling your own.Is the requirement of using an external clock mandatory? It will certainly make things more difficult. As you saw, many PWM controllers embed their own oscillator (making it a lot easier to generate a sawtooth signal internally). If you're using a full integrated class D amplifier, you may be able to feed it an external clock, but it will most likely be a multiple of the modulation frequency, and not the modulation frequency directly... so you'll probably need a PLL.What is this last requirement for exactly? Tell us more. Do you just need to control the frequency, or will it have to be fully synchronous? Will the frequency be fixed once and for all, or variable?If it's a hard requirement, you could always design your own PWM modulator, with a square to sawtooth converter (basically an integrator), but the result will be extremely disappointing unless you spend unreasonable time designing all this. And even so...Another approach could be to design it all digitally on a CPLD/small FPGA. Either way, if you're going to drive output power transistors, you'll also need to implement dead-time (otherwise your amplifier would have poor efficiency and may even fry.) For this, you could use an additional integrated half-bridge controller.If I were to implement this digitally for some reason, I would rather implement a sigma-delta modulator, and embed the dead-time controller. It would require an ADC for the input signal if you really need an analog input. Then the input clock would be multiplied with an embedded PLL to feed to modulator.But again, unless you have a very specific reason to do this, just use an integrated class-D amplifier.