TAS2557: TAS2557 EMI issue

Nic Lin

Intellectual 2020 points

Part Number: TAS2557

Team,

Customer found EMI issue on TAS2557. Below is the current SCH without output LC. When windows volume incresae to higher than 20%, EMI test will fail. Below is the test result of 20% volume. Do you have any advice of how to improve this?

over 6 years ago

0 Ivan Salazar over 6 years ago

TI__Guru** 110815 points

Hi Nic,

Output filter can be placed at the output of the device to improve EMI performance. Table 128 and Figure 148 from data sheet show some values for this filter: www.ti.com/.../tas2557.pdf
In addition, do you know if they're using Spread Spectrum mode?

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

Thanks Ivan. I will ask customer to try that value. Could you let me know how to enable SSM in PPC3 or registers?

0 Ivan Salazar over 6 years ago in reply to Nic Lin

TI__Guru** 110815 points

Nic,

Details on SSM are in data sheet section 9.3.15: www.ti.com/.../tas2557.pdf
First, the internal oscillator must be used to generate the ramp, this is done by writing 0x00 into B100_P0_R40. Then SSM mode can be enabled writing 0x01 into B0_P0_R40.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

Hi Ivan,

What about the setting in PPC3? I just found below setting but no where to enable SSM.

Regards,

Nic

0 Ivan Salazar over 6 years ago in reply to Nic Lin

TI__Guru** 110815 points

Nic,

Unfortunately SSM control is not yet integrated in PPC3. I'll comment about this with the team for next updates.
However you can select Internal for Ramp Clock and then just use I2C command to write into B0_P0_R40:
w 98 00 00
w 98 7F 00
w 98 00 00
w 98 28 01

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

HI Ivan, I am bit confused about w 98 28 01, why it is 28?

0 Ivan Salazar over 6 years ago in reply to Nic Lin

TI__Guru** 110815 points

Nic,

R40 is decimal, so in hex it is 0x28.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/6/combined_5F00_configuration_5F00_0_5F00_TuningMode_5F00_48KHz.7z

Hi Ivan,

Attached is the configuration file that was dumped from PPC3. Could you let me know where and how to add "the internal oscillator must be used to generate the ramp, this is done by writing 0x00 into B100_P0_R40. Then SSM mode can be enabled writing 0x01 into B0_P0_R40." to this file? Just to make sure that it is correct. Thanks.

0 Nic Lin over 6 years ago in reply to Nic Lin

TI__Intellectual 2020 points

There are several "w 98 28 xx" in the dump file. I am not sure where to add B100_P0_R40 and B0_P0_R40.

0 Ivan Salazar over 6 years ago in reply to Nic Lin

TI__Guru** 110815 points

Hi Nic,

Ramp clock is selected in line 10506 as shown in the below capture. The current value is 0x80 which is "PLL". You must change this to 0x00 so that is selects "Internal" instead.
SSM_EN register is not included in the cfg, however you can add a line to enable Spread Spectrum Mode.
The necessary changes are like below capture of the cfg you provided:

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

Thanks Ivan. It is quite clear!

0 Nic Lin over 6 years ago in reply to Ivan Salazar

TI__Intellectual 2020 points

Hi Ivan,
One more question, after enable SSM mode, how do I check if SSM mode is really enable or not? Seems there is no PWM output pin to check the waveform.

I also could not find RAMP_DSP register definition in datasheet. Could you share me the compelete register setting document? Thanks.

0 Ivan Salazar over 6 years ago in reply to Nic Lin

TI__Guru** 110815 points

Hi Nic,

When SSM is enabled, the output signals have a variation in the PWM switching frequency based on RAMP_CTRL bits 1-0.
There are some missing registers in the register map from data sheet. I'll verify what is safe to add and will update it, although this might not be immediate. However specifically about B100_P0_R40 it is basically just used as explained previously and it is also controlled on PPC3.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

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TAS2557: TAS2557 EMI issue