The choice of ODT impedance in RPA and DDR Tool

[george]

Dear OliverChen‌,

Our board design was done with ODT impedance 48 ohms for LPDDR4.

However, I can not find 48 Ohms in RPA and MSCALE_DDR_Tool_User_Guide provided by you.

RPAv23 :

DDR_Tool_User_Guide :

That seems to be the case in the LPDDR4 data sheet.

Does DDRTOOL work correctly when I set 48 Ohms in RPA?

Best Regards,

George

[oliver_chen · Accepted solution]

Hi george‌,

Yes, you can use 48 ohm as the ODT impedance and the DDR tool can support it. The RPA tool and guide would update it in the future.

B.R

Oliver

[george]

Dear OliverChen‌

Tell us more about TxImpedance and ATxImpedance.
We compared it to IBIS-Model for i.MX8M.

DDR_Tool_User_Guide :

IBIS-Model :

[Model Selector] DQ_DQS

Driver Settigs = TxImpedance@RPA

mal4drv_lpd4_34      LPDDR4 mal4drv27 cell  Z0=34-Ohm Driver

mal4drv_lpd4_40      LPDDR4 mal4drv27 cell  Z0=40-Ohm Driver

mal4drv_lpd4_48      LPDDR4 mal4drv27 cell  Z0=48-Ohm Driver

mal4drv_lpd4_60      LPDDR4 mal4drv27 cell  Z0=60-Ohm Driver

[Model Selector] CA_CK

Driver Settigs = ATxImpedance@RPA

mal4drv_lpd4_30_ca      LPDDR4 mal4drv20 cell  Z0=30-Ohm Driver

mal4drv_lpd4_40_ca      LPDDR4 mal4drv20 cell  Z0=40-Ohm Driver

mal4drv_lpd4_60_ca      LPDDR4 mal4drv20 cell  Z0=60-Ohm Driver

mal4drv_lpd4_120_ca      LPDDR4 mal4drv20 cell  Z0=120-Ohm Driver

The number of impedances prepared for each is different.

which one is correct?

BR,

George

[oliver_chen]

Hi george‌,

I'm sorry to make you confusion. The note in DDR_Tool_User_Guide document is complete and correct.

B.R

Oliver

[george]

Dear OliverChen‌

That means there are not enough entries in IBIS-MODEL?

BR,

George

[oliver_chen]

Hi george‌,

Although in public release, we only list the input parameters as you saw, you can use all other possible values in your test. The DDR firmware support all of them.

B.R

Oliver

[george]

Dear OliverChen‌

Thanks,

George