SGTL5000 32-PIN QFN exchangeable by 20-PIN QFN?

[Uwe]

Hello,
the SGTL5000 32-PIN QFN chip (SGTL5000XNAA3) is not available anymore. (EOL) All distributors stocks are empty.
That is the chip used on the audio shield. And that is also the chip I use for my custom board.
My idea is to replace it by the 20 pin version (SGTL5000XNLA3). That should save me from writing a new driver and be able to use the existing one.

Most of the additional 12 pins from the XNAA3 are not connected resp. are GND pads.
There are only four of them which have additional functionalities that are missing in the 20-pin version:
Pin 7, AGND (Analog Ground)
Should be the same as GND. True?
Pin 18, CPFILT (Charge Pump Filter)
Not needed. VDDx is >3.0V
Pin 31, CTRL_ADR0_CS(I²C Mode: I²C Address Select 0; SPI Mode: SPI Chip Select)
Set to GND. Only interesting for SPI?
CTRL_MODE(Mode select for I²C or SPI; When pulled low the control mode is I²C, when pulled high the control mode is SPI)
Set to GND. Means that I²C is active. Seems to be no problem because I²C is also the mode the 20-pin QFN supports.

The only essential difference I can notice is that the 20-pin QFN model only supports I²C and not SPI.
So it should be easy to use it as a replacement in the audio shield, right?

Cheers,
Uwe

 

[Uwe]

Pin 7, AGND is not connected on the audio shield. So this shouldn't be a problem.
Pin 18, CPFILT is also not connected.
Pin 31, CTRL_ADR0_CS is tied to GND which results in a I²C device address of 0001010(R/W) (R/W is the read/write bit from the I²C protocol)
The 20 QFN has exactly the same hard coded device address.

At the moment I'm almost sure that the XNAA3 can easily be replaced by a XNLA3(with some routing effort, off course). At least on the audio shield where the I²C address select is tied to GND.

 

[PaulStoffregen]

So it should be easy to use it as a replacement in the audio shield, right?

Looks that way. The only thing missing seems to be the ability to use 2 chips sharing SDA & SCL.

But I have not personally used the 20 pin version (yet). PJRC has a large number of the 32 pin chips, so we'll continue making the audio shield as-is probably until 2023.

 

[MarkT]

I presume the 32 pin variety is being dropped as its seen as over-large (!) for the typical use (mobile phone etc). A lot of phone chips are actually bare-die
BGA's these days to save space. Or it may simply be economics, more pins means more pads on the die, means larger die, means fewer chips per wafer.

 

[rvh]

Pin 7, AGND is not connected on the audio shield. So this shouldn't be a problem.

The SGTL5000 QFN-20 seems to have just a single ground via the pad on the underside of the chip. I have a layout I'm working on with separate analog and digital ground planes, that join together a long way from my SGTL5000. In that situation, which would be the better ground plane to connect the pad to? I currently have it connected to the digital ground plane thinking I don't want to corrupt the analog ground plane with the SGTL's high speed clock signal return currents. The VAG cap and VADD bypass caps go to the analog plane. Is this the right approach with this version of the chip? Thanks.

 

[rvh]

The SGTL5000 QFN-20 seems to have just a single ground via the pad on the underside of the chip. I have a layout I'm working on with separate analog and digital ground planes, that join together a long way from my SGTL5000. In that situation, which would be the better ground plane to connect the pad to? I currently have it connected to the digital ground plane thinking I don't want to corrupt the analog ground plane with the SGTL's high speed clock signal return currents. The VAG cap and VADD bypass caps go to the analog plane. Is this the right approach with this version of the chip? Thanks.

In case anyone else is using this chip with separate ground planes, I contacted NXP technical support about this. They advised me that the analog bypass and VAG capacitors need to connect to the ground pad close to the chip to be effective. So that leaves me inclined to connect the ground pad and the VAG/VADD capacitors to my analog ground plane, and only digital supply bypass caps to my digital ground plane.