onsemi MC78L08ABDR2G: Technical Specifications and Application Circuit Design
The MC78L08ABDR2G from onsemi is a classic, low-current, fixed-voltage linear regulator belonging to the renowned 78L series. This device is engineered to deliver a stable +8V output voltage at currents up to 100 mA, making it an ideal choice for powering low-power microcontrollers, sensors, op-amps, and other circuitry requiring a clean and reliable voltage rail. Its compact SOT-23 package is perfectly suited for space-constrained applications.
Key Technical Specifications
The performance of the MC78L08ABDR2G is defined by a set of critical electrical characteristics:
Output Voltage (VO): +8V ±4% (approx. 7.68V to 8.32V). This tight tolerance ensures consistent performance for connected loads.
Output Current (IO): Up to 100 mA.
Input Voltage (VI): Up to 30V. A typical recommended input voltage is at least 2V above the output, e.g., 10.5V to 12V for an 8V output, to ensure proper regulation and account for ripple.
Line Regulation: 60 mV (Typ.). This specifies the output voltage change for a given variation in input voltage.
Load Regulation: 15 mV (Typ.). This specifies the output voltage change for a variation in load current from 1mA to 40mA.
Quiescent Current (IQ): 5.5 mA (Typ.). This is the current the device consumes internally, which is not available to the load.
Dropout Voltage: 1.7V (Typ.) at IO = 40 mA. This is the minimum required difference between input and output voltage to maintain regulation.
Operating Junction Temperature (TJ): -40°C to +125°C. This wide range makes it suitable for industrial and automotive environments.
Internal Protection: The device incorporates internal short-circuit protection and thermal shutdown, safeguarding both the regulator and the load under fault conditions.
Typical Application Circuit Design
Designing a basic power supply with the MC78L08ABDR2G is straightforward, requiring only a few external components for stable operation. The standard application circuit is shown below.
```
Unregulated DC Input
(V_in: ~10.5V to 20V)
|
+++
| | C1
| | 100nF
+++
|
+-------+-----> V_out (+8V, 100mA max)
| |
| +++
| | | C2
| | | 100nF
| +++
| |
| +++
| | | C3 (Optional)
| | | 10µF (Tantalum)
| +++
| |
[MC78L08ABDR2G]
| IN | OUT
+------+------+
| | |
GND GND GND
```
C1 (Input Capacitor): A 100nF ceramic capacitor placed close to the input pin is crucial for local decoupling. It helps neutralize the effects of inductive layout and suppresses high-frequency noise on the input line.
C2 (Output Capacitor): A 100nF ceramic capacitor on the output is essential for improving transient response and ensuring stability of the regulator. It prevents oscillations and provides a immediate charge source for sudden load changes.
C3 (Output Bulk Capacitor): While often optional for stability, a larger 10µF tantalum or aluminum electrolytic capacitor is highly recommended to further improve transient response and act as a bulk storage element for the entire circuit.
Design Considerations and Best Practices
1. Heat Dissipation: Although the SOT-23 package has limited power handling capability, power dissipation must be calculated. Power dissipated PD = (VIN - VOUT) ILOAD. Ensure the junction temperature does not exceed its maximum rating. For higher currents or larger voltage drops, a heatsink or a larger package regulator (e.g., TO-220) is necessary.
2. Stability: The device is designed to be stable with low-ESR ceramic capacitors, making it easy to use with modern components.
3. PCB Layout: For optimal performance, keep the path from the input capacitor to the IC's IN and GND pins as short as possible. Similarly, the path from the OUT pin to the output capacitor should be short and direct.
ICGOODFIND: The onsemi MC78L08ABDR2G remains a highly reliable and cost-effective solution for generating localized +8V power rails in low-power electronic systems. Its robust feature set, including internal protection and wide operating temperature range, combined with a simple application circuit, makes it an excellent choice for designers across consumer, industrial, and automotive applications.
Keywords: Linear Regulator, Fixed 8V Output, 100mA, SOT-23 Package, Thermal Protection
