onsemi MC7905CD2TG: Datasheet, Pinout, and Application Circuit Guide
The onsemi MC7905CD2TG is a classic linear voltage regulator belonging to the renowned 79xx series of fixed negative voltage regulators. This device is designed to provide a stable -5V DC output voltage from an unregulated negative input voltage, making it a fundamental component in countless power supply designs for decades. Its primary function is to deliver up to 1A of output current while maintaining excellent line and load regulation.
This guide delves into the essential information for effectively utilizing this regulator, covering its datasheet specifications, pinout configuration, and a standard application circuit.
Datasheet Overview and Key Specifications
Understanding the absolute maximum ratings and electrical characteristics from the datasheet is crucial for reliable circuit design.
Output Voltage: -5V ±4% (VIN ≤ -7V, IO = 5mA to 1A, TJ = 0°C to 125°C)
Output Current: Up to 1.0A
Input Voltage Range: -7V to -25V (A minimum voltage difference of -2V between input and output is required for regulation.)
Peak Output Current: 2.2A (non-repetitive)
Line Regulation: 8mV (Typ.) (ΔVIN = -8V to -20V)
Load Regulation: 10mV (Typ.) (IO = 5mA to 1.5A)
Ripple Rejection: 62dB (Typ.) (f = 120Hz)
Operating Junction Temperature: 0°C to +150°C
Package: D2PAK (TO-263-3), a surface-mount package designed for high-power dissipation, requiring an appropriate heatsink for high-current operations.
Pinout Configuration
The MC7905CD2TG comes in a 3-pin D2PAK package. Correct connection is vital to prevent damage. The pinout is as follows:
1. Pin 1 (Input): This pin connects to the negative input voltage. The common ground reference must be more positive than this input.
2. Pin 2 (Ground): This is the common ground terminal. It serves as the reference point for both the input and output voltages.
3. Pin 3 (Output): This pin provides the regulated -5V output.
Crucial Note: Unlike positive regulators, the input and output of the 7905 are negative relative to ground. The common ground is the most positive point in the regulator circuit.
Standard Application Circuit
A basic application circuit for the MC7905CD2TG is straightforward but requires a few external components for stability and protection.
Components Required:
CIN (Input Capacitor): A 0.33μF ceramic or tantalum capacitor placed close to the regulator's input pin. It helps neutralize inductive effects from long input leads and improves stability.
COUT (Output Capacitor): A 1.0μF ceramic or tantalum capacitor placed close to the regulator's output pin. It is essential for output stability and improves transient response.
U1: MC7905CD2TG regulator.
Heatsink: A suitable heatsink attached to the tab of the D2PAK package is mandatory if the power dissipation (PD = (|VIN| - |VOUT|) IOUT) exceeds a few watts.
Circuit Operation:
The unregulated negative DC input is applied to Pin 1 (Input). The regulator internally maintains a constant -5V at Pin 3 (Output), with Pin 2 (Ground) connected to the system common ground. The capacitors CIN and COUT ensure stable operation under varying load conditions.
Typical Applications
This regulator is ideal for local on-card regulation, eliminating noise and distribution problems associated with single-point regulation. It is commonly used in:
Digital logic circuits requiring a clean -5V rail.
Op-amp dual power supplies (±12V, ±15V).
Industrial and consumer electronics power modules.
Power supply output stages for analog and digital systems.
ICGOODFIND: The onsemi MC7905CD2TG remains a highly reliable and cost-effective solution for generating a fixed -5V power rail. Its robust performance, simple implementation with minimal external components, and high ripple rejection make it a perennial favorite for engineers designing negative voltage supplies. Proper attention to heatsinking and input/output capacitor selection is the key to maximizing its performance and longevity.
Keywords: Negative Voltage Regulator, Fixed -5V Output, D2PAK Package, Linear Regulator, Power Supply Circuit
