AM625: 32 bits LPDDR4 support on AM625 with 16 bits DDRSS controller

Rich, AM625 only support 16bits data interface.  32-bit interface is not supported.  If you connect a 32bit device, you will only be able to access half of the total memory.  They would need to use an 8GB x32 device in order to access 4GB with x16

Regards,

James

James, 

Thanks!

Do we recommend using 8Gb x 8 DDR4 (ex. MT40A1G8) to support 4GB capacitor with AM625?

It will become CS0 x 16 + CS1 x16 which means any given time will only two DDR4 chip will be selected. 

Will there be driving capability consideration?

If this approach is feasible, do we have successful case and reference design also software configuration for this approach?

BR, Rich

Rich, with DDR4, there is a little more flexibility.  You can use two x8 devices on the board for the 16-bit bus.  Using two MT40A1G8 will give you a total of 16Gb (2GB).  You can also use Micron MT40A2G16 or x2 MT40A2G8 to get to 4GB.  Connection diagrams can be found in the DDR layout guidelines: https://www.ti.com/lit/pdf/sprad06

Remember that data bus can only be routed point to point (not allowed to split the data bus on the board)

Regards,

James

James, 

Do you mean 4 pcs x8 in two CS is not recommended? 

There is problem to get 2G dies so 1G dies x4 is a possible alternative. 

I remember there is customer use 4 DDR3 chips with AM335x in old day.

Will there be limitation using 4 pcs x8 1G dies since layout guideline doesn't show 4 dies reference. 

Customer even ask whether is possible to use 4 pcs x4 1G DDR4 die (MT40A2G4) on single CS to support 4GB memory. 

I personally never see x4 DDR chip but the part number is there. 

Do we have concern on Address and Control pin driving fan out capability for AM62x DDRSS? 

BR, Rich

Rich, you can't use 4 pcs of x8, that would require a T-branch of the data bus on the board.    You are restricted to 1pc x16, or 2pcs x8.  We don't support x4 devices, that would be 4 loads on the address bus, which is not supported.

Regards,

James

James, 

Understand, customer consider using 8GB (64Gb) LPDDR4 x32bit with AM625 and use only 4GB (32Gb).

Do we suggest such user case? 

Is there recommended part number if this is feasible?

BR, Rich

Rich, AM62x only supports max 2GByte LPDDR4, 8GByte DDR4.  You can achieve 8GByte with 2x MT40A4G8, dual rank

Regards,

James

James, 

I checked AM625 Data Manual and it shows 

DDR Subsystem (DDRSS)
– Supports LPDDR4, DDR4 memory types
– 16-Bit data bus with inline ECC
– Supports speeds up to 1600 MT/s
– Max addressable range
• 8GBytes with DDR4
• 4GBytes with LPDDR4

I believe you are saying if using 32 bits LPDDR4 will be up to 2GB. 

BR, Rich 

Rich, technically, AM625 does support 4GBytes with LPDDR4, but it would require using only half of a x32 8GByte device, which isn't practical since you would have to pay for double the memory.  That is why is said max 2GByte.

However, i just found out that ISSI has a x16, dual rank device IS43LQ16K02S2B, which would support 4GByte.  This device looks new, not sure of its availability.

Regards,

James