Audio Circuit Debugging Tips

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Audio debug tips

1. External component placement

2. Grounding Problems

3. Power Supply and Decoupling

4. PWM Filter

5. Heat dissipation issues

6. I2C/I2S Communication

1. Component placement

The Class D amplifier generates PWM pulses, the speaker terminals are in bridge-tied load configuration, and the speaker driver is about twice the power supply. The operating frequency is generally 384Khz to 768Khz, and the fast switching pairs have fast rise time (nS) and short pulse width, so this may cause serious RF emission interference, making the traces between the chip and the speaker become antennas, so it is important to handle component placement.

Output Filter

2. Grounding problem

- Closely related to component placement is the issue of grounding. Ideally, all components are placed in ideal locations with a solid ground plane that has zero impedance so it does not interfere with anything else and does not have any effect and poses an EMI threat to ground return currents.

-Ideally, sensitive components may need to be placed away from noisy components, with a ground plane having finite impedance. This is where it may be necessary to isolate the ground to a certain degree, but there is a risk of causing EMI hazards due to the isolation creating unwanted antennas.

Inside the chip, the analog and digital domains need to communicate with each other. The red loop below is the ground current. This means there is a return current flowing in and out of the different grounds. Due to these ground loop currents and the connection impedance between each circuit to avoid noise coupling from the digital circuit to the analog circuit. It is recommended to use different grounds to avoid the switch coupling noise through the ground, even connecting a small resistor to increase the separation can also be used.

-If possible, use small resistors to improve the distance between power ground and analog ground

-Avoid connecting digital power and analog power together

- Added power filter

3. Power supply and decoupling

Since these audio amplifiers are directly connected to PVDD for power supply, the power supply impedance is high because of the large current consumption. There are a lot of internal circuits with protection functions built in, such as UVP (Under Voltage Protection), OCP (Over Current Protection), OTP (Over Temperature Protection), both UVP and OCP will generate false triggers due to power supply spikes, so proper supply decoupling may help it.

4. PWM Waveform Edge

Normal PWM for a Class D chip output rise time is about 2nS, the frequency of the edge current will be around 200Mhz, power supply decoupling on this chip is critical to keep the current loop as small as possible and avoid propagating interference. The switching transients can be very high, so we recommend placing ceramic capacitors next to each amplifier supply pin. Due to the large currents, a minimum of 1uF + 0.1uF per pin is recommended. A direct trace from VDD to the main capacitor with the same layer is required, the capacitor ground connection should be the same as the amplifier chip ground.

In higher power Class D amplifiers, typically with output powers greater than 10 W, a filter at the output of the amplifier is a necessity. The filter is passive in nature and each filter uses an inductor and capacitor output termination. Hence, it is called an LC filter. Selection of the proper LC filter component is critical to meet the desired audio performance, efficiency, EMC/EMI requirements and final cost of the application. This application report serves as a guide to assist the LC filter component portion of the Class D amplifier to meet the target design goals of the end system. Some TI Class D audio amplifiers support multiple output configurations in a single device. This allows for a high degree of flexibility in the end application.

The PWM filter can adopt different modes to support the board amplifier types, such as AD modulation, BD modulation, 1SPW, hybrid... etc. In addition, the PWM has different configurations to match BTL mode, PBRL mode and SE mode.

Bridge Tied Load (BTL)

Parallel Bridge Tied Load (PBTL)

Single-ended (SE)

TI has developed an LC calculation tool to optimize the value and make it easier for end customers to design their own filters. Here is the download address. Please make sure your circuit matches the modulation method you choose.

5. Heat dissipation problem

Since power amplifiers are high current devices, heat is a challenge for those designers.

In a Class D audio amplifier, the PWM switching frequency mainly affects the MOSFET loss and the inductor loss. Using a large inductor reduces the PWM switching frequency and improves the heat dissipation performance. At large outputs, the LC filter can achieve better thermal performance than ferrite beads.

Place the power amplifier device away from the edge of the PCB and avoid using traces or cross-wires to cut off the heat flow from the audio amplifier device to the surrounding area.

• Solution:

Use 1SPW mode to reduce switching loss

Avoid placing other heat-generating components or structures near the amplifier.

Use more PCB layers to provide more

The thickness of copper and PCB layers have a big impact on thermal performance. For the EVM board, it is 4 layers and 2Oz copper.

6. I2C / I2S Communication

I2C communication failed

- The software is configured with the wrong device address

- Data edge change error

- Wrong/weak signal or wrong voltage level

- Ground pull-up resistor or capacitor error causes slow rise to trigger circuit error

- Poor grounding or connection to a noisy ground

I2S communication failed

- Set the wrong I2S format, because there are many different I2S formats, such as DSP, left-justified, right-justified and TDM, and the bit length and offset are also different

- Wrong level / Too much noise

- The wiring is too long and interfered with

• Solution:

Reduce the resistance value

Reduce the capacitance value

Configure the matching format

Reduce signal noise