The **UR5595-SH2-R** is a high-performance **Linear Voltage Regulator** specifically designed to provide termination voltage ($V_{TT}$) for DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory). It is commonly used in PC motherboards, workstations, and embedded systems to ensure signal integrity. --- ### 1. General Specifications The device acts as a sink/source regulator, meaning it can both provide current to the bus and absorb current from it to maintain a stable voltage level. | Parameter | Specification | | :--- | :--- | | **Type** | DDR Termination Regulator ($V_{TT}$) | | **Output Current** | ±2.0A (Continuous) / ±3.0A (Peak) | | **Input Voltage ($V_{CC}$)** | 2.25V to 5.5V | | **Reference Voltage ($V_{REF}$)** | 0.75V (Typical, usually 1/2 of $V_{DDQ}$) | | **Package Type** | HSOP-8 (Exposed Pad for thermal dissipation) | | **Accuracy** | ±1.5% to ±2% | --- ### 2. Key Electronic Features * **Bidirectional Current Capability:** Unlike standard linear regulators that only "push" current, the UR5595 can "pull" (sink) current. This is essential for DDR buses where signals toggle rapidly. * **Buffered Reference:** It includes a buffered reference voltage output ($V_{REF}$) which is used by the memory controller and the RAM chips as a comparison threshold. * **Thermal Protection:** Includes internal thermal shutdown circuitry to prevent the chip from burning out under high load. * **Current Limiting:** Protects the device and the PCB traces during short-circuit conditions. * **Soft Start:** Reduces inrush current during power-up to prevent voltage spikes on the rails. --- ### 3. Pin Configuration (HSOP-8) | Pin # | Name | Description | | :--- | :--- | :--- | | 1 | **VIN** | Power input for the internal control logic. | | 2 | **GND** | Ground reference. | | 3 | **REFOUT** | Buffered reference voltage output ($1/2 V_{DDQ}$). | | 4 | **REFIN** | Reference voltage input (sets the target $V_{TT}$). | | 5 | **VCNTL** | Control logic input voltage. | | 6 | **VTT** | Regulated termination voltage output. | | 7 | **VTT** | Regulated termination voltage output (connected to Pin 6). | | 8 | **EN** | Enable pin (High = On, Low = Shutdown/High Impedance). | --- ### 4. Typical Application Circuit The UR5595 is typically placed between the $V_{DDQ}$ rail and the memory bus termination resistors. ```mermaid graph LR VDDQ[VDD Memory Rail] -->|Voltage Divider| REFIN[UR5595 REFIN] VCC[System Power] --> VIN[UR5595 VIN] UR5595 --> VTT[Termination Bus] UR5595 --> VREF[Memory Ref Voltage] ``` --- ### 5. Selection Considerations When using the **UR5595-SH2-R**, designers must pay close attention to: 1. **Thermal Management:** The "SH2" suffix indicates an HSOP-8 package with a thermal pad. This pad **must** be soldered to a large ground plane to dissipate heat, as linear regulation at 2A generates significant thermal energy ($P = (V_{IN} - V_{OUT}) \times I$). 2. **Capacitor Selection:** Low ESR (Equivalent Series Resistance) ceramic capacitors are required on the $V_{TT}$ output to maintain stability during high-frequency switching. ---