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docs/developers/hardware_ref/power/dram.md

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+A separate [Sylergy SY8088][1] Buck DC/DC SMPS chip is used to provide
+the DDR2 +1V8 DDR2 DRAM power.
+
+This is because the AXP20x is originally the PMU (Power Management
+Unit) used by most Allwinner SoCs (A10, A13 and A20), which do not
+integrate SDRAM, so the board designer has a wide choice of memory
+option: DDR2, DDR3, DDR3L, LPDDR3, LPDDR4 with various voltage
+requirements.
+
+But no specific PMIC was created for the Allwinner V3s used in the
+FunKey device which however integrates a fixed SiP (System In Package)
+512Mbit (64MB) DDR2 SDRAM.
+
+We thus have to design a separate SMPS (DC-DC) power supply for
+providing the +1.8V 1A required for the DDR2 DRAM power supply.
+
+For this purpose, we followed closely the [Allwinner Reference
+Design][2].
+
+Here is the corresponding DRAM Power schematics:
+
+![DRAM Power Schematics](/assets/images/DRAM_Power_Schematics.png)
+
+Nothing very fancy here: the SMPS chip **U4** has its required input
+filter capacitor **C37** and output capacitors **C65** and **C73**.
+
+The low-profile ferrite-core power inductor **L6** (rated with a
+saturation current of 1.76A and low < 0.1 Ω resistance) provides the
+DC-DC energy storage element.
+
+The **R20**/**R23** precision voltage divider provides the required
++0.6V feedback voltage from the +1.8V output voltage by having a 1/3
+resistor ratio.
+
+The last component is a pull-up resistor **R19** which ties the SMPS
+chip enable input to its active level permanently. The pull-up voltage
+is +3.0V (just as in the original reference design), probably as it is
+the next higher voltage available, in order to limit the current in it
+to its lowest possible value.
+
+[1]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C79313_SY8088AAC_2017-03-29.PDF
+[2]: https://github.com/Squonk42/V3s_Documentation/blob/master/V3S_CDR_STD_V1_0_20150514.pdf
+[3]: https://datasheet.lcsc.com/szlcsc/Silergy-Corp-SY8088AAC_C79313.pdf
+[4]: https://datasheet.lcsc.com/szlcsc/1901241230_LOWPOWER-LP3220S-AB5F_C324565.pdf
+[5]: https://www.diodes.com/assets/Datasheets/AP3418.pdf
+
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+includes/glossary.md
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