TL5001 as a audio PWM - Page 1
Forum section: electronics / beginners

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 01:15:08 am
content: Hello everyoneI want to develop a PWM modulator for an AM transmitter on a TL5001 chip (https://www.lcsc.com/product-detail/DC-DC-Converters_Texas-Instruments-TL5001CDR_C2867084.html). An audio signal is received at the input, linear (0...0.5 V), at the output there should be a PWM signal of 100 kHz, the duty cycle of which should vary from 0% to 100% with the sound.I have drawn 6 options for connecting the chip. Which one is the correct one?

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 10:56:18 am
content: Information for understanding. Purpose of the microcircuit pins.1. Output. The microcircuit has an open collector, so a pull-up resistor is needed on the + power supply. The resistor resistance should provide the required current in the load and not exceed the maximum current of the microcircuit itself. My load will be the optodriver LED, so 330 Ohm is the optimal value with a 5V supply.2. Positive supply. No questions here.3. Compensation. The pin is needed when the microcircuit works for its intended purpose - a PWM voltage converter. But is this pin needed when the microcircuit will work as a PWM audio modulator?4. Feedback. The pin is needed to stabilize the output voltage when the microcircuit works as a PWM voltage converter. It seems to me that this pin has a very small voltage range, so it cannot be used as an input for audio modulation.5. Short circuit protection. When the chip works as an audio modulator, this protection is not needed. How to disable it correctly? A resistor to the positive power supply? Or a capacitor to ground?6. Adjusting the dead time. It seems to me that if I feed an audio signal to this input, I will get what I want - 100% PWM audio modulation. Am I right or not?7. Setting the PWM frequency. Everything is simple here and there are no questions.8. Ground, no questions.It seems to me that the correct circuit is either number 3 or number 4. Help me figure it out.

author: shabaz
author_rank: Frequent Contributor
timestamp: June 07, 2025, 11:25:18 am
content: Physically the wiring differences are small. Why don't you try them out, see the effects of each and decide what works for your needs?

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 11:28:36 am
content: Quote from: shabaz on June 07, 2025, 11:25:18 am100kHz is the frequency at which you already need to make a printed circuit board for a high-quality result. The result will be worse on the manual circuit board and "wiring". And in order to develop and then order a printed circuit board at the factory, I need to find out which option would be the right one.

author: shabaz
author_rank: Frequent Contributor
timestamp: June 07, 2025, 11:37:56 am
content: There are plenty of ways to prototype. Besides, you could easily make the PCB have resistor links to try the various topologies. It makes little sense not to prototype or at least simulate before committing to a final design.

author: MariuszD
author_rank: Regular Contributor
timestamp: June 07, 2025, 12:10:42 pm
content: No one is correct.I don't see the point in this design method of creating multiple schematics and asking which one is good. Is there AI involved?Ask how to properly connect each pinpin 1, 2, 8 in ver 1 is okpin 7 is ok but resistor should be 100kpin 6 leave it NC (dead time not used)pin 5 connect to GND (SCP not used)pin 3, 4 make inverting amplifier.Quote from: AlexRG on June 07, 2025, 11:28:36 amIt's not true. RF circuit can be made with dead bug on ground plane style. Not only at 0,1MHz but much higher.QuoteThat is interesting. How do you want to do it?

author: shabaz
author_rank: Frequent Contributor
timestamp: June 07, 2025, 12:50:20 pm
content: Quote from: MariuszD on June 07, 2025, 12:10:42 pmIf you want to run your microphone some distance away from the transmission, to make your location difficult to locate, then I can see why someone may want to use PWM between mic circuitry and the rest of the transmitter. Not sure people should be helping without trying to understand the actual context, because it doesn't sound like an innocent request for information.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 12:50:38 pm
content: Quote from: MariuszD on June 07, 2025, 12:10:42 pm1. To which pin should I connect the audio signal and reference voltage, to pin 3 or pin 4?2. If to pin 3, what to do with pin 4?3. If to pin 4, what to do with pin 3?4. What should be the voltage interval "from" and "to" according to the datasheet on pin 3 or pin 4 to get PWM modulation from 0% to 100% at the output?Please provide a quote from the datasheet about this.https://www.lcsc.com/datasheet/lcsc_datasheet_2411121145_UTC-Unisonic-Tech-TL5001G-1_C7509624.pdfThe only place in the datasheet that indicates a duty cycle amplitude of 0-100% is the dead time pin. Maybe it is better to feed the audio signal to it?

author: MariuszD
author_rank: Regular Contributor
timestamp: June 07, 2025, 01:26:04 pm
content: Quote from: AlexRG on June 07, 2025, 12:50:38 pmQuoteTwo resistors R43 and R44 are needed to complete inverting amplifier and make input.Dead time pin can be used instead FB

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 01:36:23 pm
content: Quote from: MariuszD on June 07, 2025, 01:26:04 pmTo create PWM modulation, a triangular (sawtooth) signal is used, it is fed to the comparator, where the modulating signal is also fed. See the diagram:The blue arrow is the sawtooth signal from the generator.The green arrow is the modulating signal from the dead time pin.The red arrow is the modulating signal from the compensation pin.Now look at the datasheet. The interval for compensation is 0.95-1.05V, that is, the amplitude is only 100mV! This is a very small amplitude interval to feed an audio signal.Now look at the dead time. The interval for dead time is 0.7-1.3V. That is, 600mV. This is exactly the average amplitude of the linear audio signal.1) set the dead time pin to 1V reference voltage, this will give a 50% duty cycle of the PWM at the output.2) feed the audio signal to the same pin. When its amplitude is 0-600mV, the output will have a PWM duty cycle amplitude of 0-100%Or am I wrong somewhere?

author: shabaz
author_rank: Frequent Contributor
timestamp: June 07, 2025, 02:00:05 pm
content: Quote from: MariuszD on June 07, 2025, 01:26:04 pmWhat bit of "it doesn't sound like an innocent request for information" didn't you understand?

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 02:42:01 pm
content: Quote from: shabaz on June 07, 2025, 12:50:20 pmThere is a civil radio communication at a frequency of 27 MHz, which uses AM modulation. Please stop writing accusations, spam and flood in my topic.

author: shabaz
author_rank: Frequent Contributor
timestamp: June 07, 2025, 03:04:47 pm
content: Quote from: AlexRG on June 07, 2025, 02:42:01 pmThat doesn't hold water. You specified 0.5-7MHz in your other thread regarding a receiver portion of circuitry.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 07, 2025, 03:15:28 pm
content: Quote from: MariuszD on June 07, 2025, 12:10:42 pmThe linear modulator has a very low efficiency, so it is better to use a PWM modulator, whose efficiency is close to 95%. The circuit is very simple. When a 100 kHz signal with a duty cycle of 50% comes out of the PWM chip, after the LPF there will be 50% of the supply voltage. With a supply of 24 V, this will be 12 V. The AM transmitter will emit a carrier with a power of 12 V. When an audio signal is fed to the PWM chip, the duty cycle of the 100 kHz signal will change from 0% to 100%, as a result, after the LPF, the voltage will change from 0 V to 24 V in time with the audio, providing modulation to the transmitter.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 08, 2025, 01:35:25 am
content: Quote from: MariuszD on June 07, 2025, 01:26:04 pmDeveloped a printed circuit board for two variants. Let's see which one is better.One more question. If the audio voltage in the first or second option exceeds 0.6V, what will happen to the PWM signal at the output? Will it disappear or just start to distort?

author: shabaz
author_rank: Frequent Contributor
timestamp: June 08, 2025, 02:48:31 am
content: So you're hoping no-one recalls you were caught out a few messages earlier, trying to mislead regarding the frequencies of operation for your transceiver?

author: AlexRG
author_rank: Regular Contributor
timestamp: June 08, 2025, 02:57:58 am
content: Quote from: shabaz on June 08, 2025, 02:48:31 amI wrote a report on you, for false, idiotic accusations, flood and offtopic. I hope the moderators will take action against you, since you do not understand the request not to write idiotic accusations and not to flood.

author: shabaz
author_rank: Frequent Contributor
timestamp: June 08, 2025, 03:21:44 am
content: It's all precisely on-topic. It's _very_ relevant that in your other concurrent thread you are developing for a frequency spectrum that is very common for military communications, whilst now claiming you're targeting a 27 MHz band.

author: MariuszD
author_rank: Regular Contributor
timestamp: June 08, 2025, 08:03:38 am
content: Quote from: AlexRG on June 07, 2025, 01:36:23 pmOscillator voltage swing is between 0.7 and 1.3V COMP and DTC should have same range. There is no 0.95-1.05V range in datasheet. FB in usual SMPS circuits have very small range because amplifier is set to high gain. Gain can be set <1It can be done with FB/COMP it can be done with DTC. Used input should be set to 100%Quote from: AlexRG on June 07, 2025, 01:36:23 pmNo its not wrong.DTC pin is current source so reference voltage should be little lower than 1V.

author: MariuszD
author_rank: Regular Contributor
timestamp: June 08, 2025, 08:14:07 am
content: Quote from: AlexRG on June 07, 2025, 03:15:28 pmFor that purpose I would use integrated class D amplifier. It is PWM but optimised for low THD. Higher PWM frequency, easier to filter out.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 08, 2025, 08:33:28 am
content: Quote from: MariuszD on June 08, 2025, 08:14:07 amThe block diagram of the modulator that I drew above is essentially the same class D amplifier. Only usually in amplifiers, the constant component is removed from the output so that it does not damage the speaker. In this case, on the contrary, there is a constant component and it is needed, because it sets the initial carrier frequency level.What about the stability of the PWM signal, depending on the level of the audio signal? If the audio signal exceeds the limit, will the output PWM signal stop? If it stops, it's bad... In real work, this will turn off the am transmitter when the audio peaks are too high.

author: MariuszD
author_rank: Regular Contributor
timestamp: June 08, 2025, 02:08:56 pm
content: Quote from: AlexRG on June 08, 2025, 08:33:28 amSCP can be disabled by connecting it to the ground

author: EEVblog
author_rank: Unknown
timestamp: June 10, 2025, 12:13:26 am
content: Quote from: AlexRG on June 08, 2025, 02:57:58 amNo storms in a teacup please.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 26, 2025, 04:01:52 pm
content: Quote from: MariuszD on June 07, 2025, 01:26:04 pmThe printed circuit board arrived from the factory. I developed several options at once, mine worked). SCP to ground. FB to ground. Audio signal to the DTC pin. With a 120 kOhm resistor, PWM will be 81 kHz. Duty cycle amplitude 0-100%. Audio signal amplitude 0..600 mV peak-to-peak. When the input audio frequency signal is exceeded, the PWM generation is not interrupted. Great!

author: AlexRG
author_rank: Regular Contributor
timestamp: June 26, 2025, 04:04:16 pm
content: Some photos. And a PWM signal modulated by an AF signal of 1 kHz. The amplitude of the AF signal is 30 mV, 100 mV, 300 mV and 380 mV. The greater the amplitude of the AF signal, the wider the duty cycle of the PWM.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 26, 2025, 05:27:53 pm
content: There is only one thing I can't understand. This chip is an open collector. So the output needs to be connected to the + power supply, which is what I did. The resistor is 330 Ohm. There is no load, only the oscilloscope probes. Why is the lower shelf of the PWM signal at about 1.2 V, and not 0 V (blue line).

author: oPossum
author_rank: Super Contributor
timestamp: June 26, 2025, 06:07:32 pm
content: Datasheet page 8Output saturation voltage / IO = 10 mA / 1.5 V typical

author: AlexRG
author_rank: Regular Contributor
timestamp: June 26, 2025, 06:23:13 pm
content: Quote from: oPossum on June 26, 2025, 06:07:32 pmSo, the minimum shelf is ~1V, is this normal behavior?

author: AlexRG
author_rank: Regular Contributor
timestamp: June 26, 2025, 06:59:37 pm
content: In any case, I found a simple solution, an additional 2N7000 field-effect transistor at the output. Now the amplitude of the PWM is exactly 0-5V. Perfect.