SSM2604 Rout, Lout Bias Voltage


In a product of our company that uses the SSM2604, in some circumstances which are not clear to us, one or both of the outputs Rout / Lout are biased to a voltage different from that on Vmid pin.

While Vmid is at 1,65V (Vcc / 2) one or both of the outputs sometimes are biased at 2,9V for example. Other voltage levels can also be observed.

This results in distortion and noise.

CONTROL REGISTER SEQUENCING is done in the following manner:

        Registers are written in this order with the given values.

0x34, 0x00, 0x80,     //R0  00110100  00000000 10000000 -> |0011010 0|0000000|010000000
0x34, 0x02, 0x80,     //R1  00110100  00000010 10000000 -> |0011010 0|0000001|010000000
0x34, 0x08, 0x10,     //R4  00110100  00001000 00010000 -> |0011010 0|0000100|000010000
0x34, 0x0A, 0x06,     //R5  00110100  00001010 00000110 -> |0011010 0|0000101|000000110
0x34, 0x0C, 0x17,     //R6  00110100  00001100 00010111 -> |0011010 0|0000110|000010111  // Enables Vmid! Vmid.

// C starts charging.

0x34, 0x0E, 0x0A,     //R7  00110100  00001110 00001010 -> |0011010 0|0000111|000001010

wait for 500mS

0x34, 0x12, 0x01,     //R9  00110100  00010010 00000001 -> |0011010 0|0001001|000000001 // Set active bit.

Also we are slightly confused about the control register sequencing described in the datasheet.

In the datasheet REV.A of SSM2604 on page 15 is stated that after this control sequence, the bit D4 of Register R6 also should be cleared. Unfortunately the SSM2604 has no function assigned to this bit...

This leaves room for doubts about the correctness of the mentioned register sequencing.

Please help us to identify and solve this issue.

Best regards,

Stephan Heep

  • No feedback? Ok, no problem.

    The mentioned product is based on Circuit Note 0282 and uses ADV7611, ADV7125, SSM2604 and a MCU as I2C master.
    After digging further into this issue I have found out that it is not related with the control register sequencing as I thought initially.

    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. Disable manual Hot Plug Assert of ADV7611

    9. Set Hot Plug Assert of ADV7611 high

    10. Enable internal EDID (ADV7611)

    In two out of ten times, during step 9. the odd voltage levels appear causing audible distortion.

    Everything else works fine.

    Maybe now someone has got an idea of what might be wrong.