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TPA3245: TPA32XX LOW SIDE POWER SUPPLY PROBLEM

Part Number: TPA3245

Hello, i have just finished my pcb, on wich i will include some tpa 3245 chips. There will be multiple tpa chips,one for each way (3 way system), the high voltage power supply will be from an 300w toroïdal transformer and the low voltage power supply will be of an set of 3X18650 3300mah batterys in serie, with a bms, to get the maximum sound quality out of the system. But i have a relatively important ask: as the power output is directly from the batteries (whose the signal quality is the best possible among all the power supply solutions, the signal is linear and almost free of any noise), and the charge of thoses batterys is important, is it realy usefull to put the high frequency RC filter (where there is a resistor that dissipate power) before the GVDD_AD and GVDD_CD pins? I also see that, those resistors aren't present on the EVM of the tpa3245 (only a 100nf capacitor to bypass very high frequency signals), but this board use a linear regulator that, by definition, generate more noise than batterys. The set on batterys will be connected to all of the amplifiers of the board (3), so the power supply will be common .Did you just advise me to put 100nf capacitor or more, like 220nf for example, or it's necessary, regarding of my configuration, to put resistors to form an rc filter?

Thanks in advance.

  • Hi Lulu,

    GVDD is for powering the gate driver. Some noise on it won't affect the sound quality. You may just use a 0.1uF capacitor here.

    Thanks!

    Regards,

    Hao

  • Hello, thanks for the usefull answer. 

    I just have an ultimate ask. Why is there two RC filters allocated fro each GVDD pins GVDD_AB and GVDD_CD), that's in case where power supply for each pin is different? Because, i don't enderstand the idea of putting multiples RC filters in parallel instead of one in serie. Also, as the system will be powered from 2 uncorrelated power supplies, when the high power supply will be released (thanks to a simple switch, activated manually), can the low power secondary supply (from a 3s battery to GVDD_AB, GVDD_CD and VDD supply pins) be activated later (thanks to a second switch, manually), i mean, is it possible to introduce an initialisation delay between those two power feeding units, or it will affect chip's behaviour?

    Thanks for your adcome reply.

  • Hi,

    I think the R-C is actually not used as a filter... 0.1uF is high frequency decoupling cap, which need to be placed closely to pin. Resistor is simply used to indicate the current consumption on the GVDD_x.

    If there is a battery to as a second power source, I think you may use a dedicate IC, maybe something called "ORing" devices. Or the system will be not able to do the seamless transition between two power supplies.

    Any further question, please let us know. Thanks!

    Regards,

    Hao

  • Hello, i searched the utility of this famous RC filter on the datasheet and found it : "Although supplied from the same 12-V source, separating to GVDD_AB, GVDD_CD, and VDD on the printed-circuit board (PCB) by RC filters (see application diagram for details) is recommended. These RC filters provide the recommended high-frequency isolation. Special attention should be paid to placing all decoupling capacitors as close to their associated pins as possible. In general, the physical loop with the power supply pins, decoupling capacitors and GND return path to the device pins must be kept as short as possible and with as little area as possible to minimize induction". 

    I have an another question: Can the 1uf decoupling capacitors for AVDD and DVDD regulator's can be of a higher value like 2.2 or 3.3uf? If so, is it better?

  • Hi Lulu,

    We haven't tested the part with 2.2uF or 3.3uF decoupling capacitors for AVDD and DVDD regulators so we can't guarantee that the device will behave. 

    Regards,

    Robert Clifton