### 54LS347 Technical Overview The **54LS347** is a BCD-to-Seven-Segment Decoder/Driver belonging to the Low-power Schottky (LS) family of TTL integrated circuits. It is specifically designed to drive common-anode LED displays. The "54" prefix indicates that this is a **military-grade** component, capable of operating in a wider temperature range than the standard "74" series. --- ### 1. Key Features and Specifications | Feature | Specification | | :--- | :--- | | **Logic Family** | Low-power Schottky (LS) | | **Operating Voltage** | 4.5V to 5.5V | | **Operating Temperature** | -55°C to 125°C | | **Output Type** | Open-Collector | | **Output Voltage (Max)** | 15V (High Voltage) | | **Package Types** | DIP, Flatpack, LCC | --- ### 2. Functional Description The 54LS347 takes a 4-bit Binary Coded Decimal (BCD) input and converts it into the logic necessary to drive a 7-segment display (segments $a$ through $g$). #### Special Inputs/Functions: * **Lamp Test ($\overline{LT}$):** When pulled LOW, all segments turn on (displays "8") to check if segments are functional. * **Blanking Input ($\overline{BI}$):** When LOW, all segment outputs are forced OFF regardless of the BCD input. * **Ripple Blanking Input ($\overline{RBI}$):** Used for zero suppression in multi-digit displays (turns off the display if the value is zero). --- ### 3. Pinout Configuration A standard 16-pin layout for the 54LS347: | Pin Number | Symbol | Description | | :--- | :--- | :--- | | 1, 2, 6, 7 | B, C, D, A | BCD Inputs (A is LSB) | | 3 | $\overline{LT}$ | Lamp Test (Active Low) | | 4 | $\overline{BI}/\overline{RBO}$ | Blanking Input / Ripple Blanking Output | | 5 | $\overline{RBI}$ | Ripple Blanking Input | | 8 | GND | Ground | | 9 - 15 | e, d, c, b, a, g, f | Seven-Segment Outputs (Active Low) | | 16 | $V_{CC}$ | Supply Voltage | --- ### 4. Logic Circuit Implementation The outputs are **Open-Collector**, meaning they require external pull-up resistors or a direct connection to the segments of a **Common-Anode** LED display. ```mermaid graph LR BCD_Input[BCD Input A,B,C,D] --> Decoder[54LS347 Logic] Decoder --> Seg_a[Segment a] Decoder --> Seg_b[Segment b] Decoder --> Seg_n[...] ``` --- ### 5. Difference between 54LS347 and 54LS47 The primary difference between these two chips is the **Maximum Output Voltage**: * **54LS47:** Rated for up to **15V** at the outputs. * **54LS347:** Often cited in datasheets as a lower voltage or specific variant of the 47, but in modern contexts, it is virtually identical to the 47 except for specific voltage tolerances or manufacturing origins. Always check the manufacturer-specific datasheet for $V_{OH}$ limits.