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Why does SSM2604 sometimes bias Rout at 2,5V?

Question asked by S_Heep on Jul 9, 2018

On a product based on Circuit Note 0282 using ADV7611, ADV7125, SSM2604 and a MCU as I2C master, sometimes the outputs Rout and Lout of SSM2604 are biased with voltages other than Vmid (1,65V).  This happens while the voltage on Vmid is stable at Vcc/2.

 

The odd bias voltage levels on the SSM2604 audio outputs appear occasionaly after manipulating the HPA registers of ADV7611.

 

According to the example C code of CN0282 the following is done:

1. Send reset command to ADV7611

2. Wait 1000mS

3. Write the scripts to the ADV7611 and SSM2604 (respecting the control register sequence of SSM2604)

4. Enable manual Hot Plug Assert of ADV7611

5. Set Hot Plug Assert of ADV7611 low

6. Disable internal EDID of ADV7611 

7. Write EDID data to ADV7611 

8. Set Hot Plug Assert of ADV7611 high

9. Disable manual Hot Plug Assert of ADV7611

10. Enable internal EDID (ADV7611)

 

In two out of ten times, during step 8. the odd voltage levels appear causing audible distortion.

Everything else works fine.

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