Clarification Required: DRAM Block B Necessity with Micron MT53E1G32D2FW 4GB LPDDR4 on STM32MP257
Dear Team,
I hope this email finds you well.
I am writing to seek your expert clarification on a critical hardware design decision we are currently evaluating for our STM32MP257-based custom board.
--- Current Memory Configuration ---
• SoC : STM32MP257
• Memory Part : Micron MT53E1G32D2FW-046 WT:C
• Type : LPDDR4
• Density : 32 Gbit (4 GB)
• Organization: 1 x32 (Dual Channel — Channel A + Channel B)
--- Our Understanding from ST Documentation ---
Based on our research of the following official ST documents:
1. AN5723 (Rev 3, Aug 2024) :
"Interface width is 32-bit when full-populated, or 16-bit when half-populated."
2. AN5724 — DDR Routing Guide:
"For the 16-bit LPDDR4 interface, one 16-bit LPDDR4 is used in point-to-point connection. With this configuration it can drive up to 2 Gbyte memory."
3. AN5489 (Rev 6, Sep 2025) :
STM32MP257 supports both 16-bit (half-populated) and 32-bit (full-populated) LPDDR4 configurations.
Our understanding is:
• If using a native x16 LPDDR4 device → DRAM_B is NOT required (half-populated, 2 GB)
• If using our current 1x32 device (Micron MT53E1G32D2FW) → DRAM_B IS required (full-populated, 4 GB), since it is a dual-channel x32 device that needs both Channel A and Channel B connected simultaneously
--- Clarification Requested ---
Could you kindly confirm or correct the following:
1. With our current Micron MT53E1G32D2FW (x32, 4 GB) device, is it safe and supported to leave DRAM_B unconnected?
2. If DRAM_B can be left unconnected with this x32 device, would the DDR PHY training still pass successfully at boot?
3. If DRAM_B must be connected for this specific device, would switching to a x16 LPDDR4 device (e.g., Micron MT53E1G16D2FW) be the correct approach to eliminate DRAM_B routing?
This clarification is critical for us before we proceed with PCB routing, as it directly impacts our layer stack-up, routing complexity, and BOM decisions.
Thank you very much for your time and guidance. We look forward to your expert advice.