# Dallas DS1220Y NVRAM → FRAM Replacement Adapter

## DS1220Y → FM16W08 / FM18W08

This PCB adapter replaces a **Dallas DS1220Y** battery-backed NVRAM with a **Ramtron/Cypress FM16W08** or **FM18W08** ferroelectric RAM (FRAM), eliminating the internal lithium battery dependency entirely.

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## Background

The Dallas DS1220Y integrates a 2K × 8-bit SRAM with a built-in lithium cell and control circuitry. After 10–15 years the internal battery depletes, causing the chip to lose its stored data on power-off. Since the battery is sealed inside the package, the only solution is to replace the entire chip.

FRAM (Ferroelectric RAM) is a non-volatile memory technology that retains data without any battery, has effectively unlimited write endurance (≥10^12 cycles), and is pin-compatible with the Dallas parts when used with this adapter.

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## Compatibility

| Original part | Replacement FRAM |

|---------------|-----------------|

| Dallas DS1220Y | FM16W08-SG (or FM18W08-SG) |

Both **FM16W08** (64 Kbit, 8K × 8) and **FM18W08** (256 Kbit, 32K × 8) are supported — both operate over −40 °C to +85 °C and 2.7 V to 5.5 V.

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## Components

| Designator | Value / Part       | Package    | Notes                        |

|------------|--------------------|------------|------------------------------|

| IC1        | FM16W08-SG / FM18W08-SG | SOIC-28 (1.27 mm pitch) | Cypress/Infineon FRAM |

| C1         | 100 nF, 50 V, X7R | 0805       | Decoupling capacitor         |

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## Files

| File / Folder       | Description                              |

|---------------------|------------------------------------------|

| `1220.kicad_pcb`    | KiCad PCB layout                        |

| `1220.kicad_sch`    | KiCad schematic                         |

| `production/`       | Gerber files + BOM ready for manufacturing |

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## Installation

1. **If you want to preserve the stored data**, read out and save the contents of the original DS1220Y before removal.

2. Remove the original Dallas DS1220Y from the host board.

3. Solder the FM16W08-SG or FM18W08-SG to the adapter PCB (IC1) and the 100 nF decoupling capacitor (C1).

4. Write the previously saved data into the new FRAM before installation.

5. Insert the adapter into the socket or solder it to the pads where the original DS1220Y was located.

6. No firmware or software changes are required — the FRAM is fully transparent to the host system.