The LM2931 series consists of positive fixed and adjustable output
voltage regulators that are specifically designed to maintain proper
regulation with an extremely low input−to−output voltage differential.
These devices are capable of supplying output currents in excess of
100 mA and feature a low bias current of 0.4 mA at 10 mA output.
Designed primarily to survive in the harsh automotive environment, these devices will protect all external load circuitry from input fault conditions caused by reverse battery connection, two battery jump starts, and excessive line transients during load dump. This series also includes internal current limiting, thermal shutdown, and additionally, is able to withstand temporary power−up with mirror−image insertion. Due to the low dropout voltage and bias current specifications, the LM2931 series is ideally suited for battery powered industrial and consumer equipment where an extension of useful battery life is desirable. The ‘C’ suffix adjustable output regulators feature an output inhibit pin which is extremely useful in microprocessor−based systems.
Features:
• Input−to−Output Voltage Differential of < 0.6 V @ 100 mA
• Output Current in Excess of 100 mA
• Low Bias Current
• 60 V Load Dump Protection
• −50 V Reverse Transient Protection
• Internal Current Limiting with Thermal Shutdown
• Temporary Mirror−Image Protection
• Ideally Suited for Battery Powered Equipment
• Economical 5−Lead TO−220 Package with Two Optional Leadforms
• Available in Surface Mount SOP−8, D2PAK and DPAK Packages
• High Accuracy (±2.5%) Reference (LM2931AC) Available
• NCV Prefix for Automotive and Other Applications Requiring
Unique Site and Control Change Requirements; AEC−Q100
Qualified and PPAP Capable
• Pb−Free Packages are Available
Applications
• Battery Powered Consumer Products
• Hand−held Instruments
• Camcorders and Cameras
APPLICATIONS INFORMATION:
The LM2931 series regulators are designed with many protection features making them essentially blow−out proof. These features include internal current limiting, thermal shutdown, overvoltage and reverse polarity input protection, and the capability to withstand temporary power−up with mirror−image insertion. Typical application circuits for the fixed and adjustable output device are shown in Figures 17 and 18. The input bypass capacitor Cin is recommended if the regulator is located an appreciable distance (≥ 4″) from the supply input filter. This will reduce the circuit’s sensitivity to the input line impedance at high frequencies. This regulator series is not internally compensated and thus requires an external output capacitor for stability. The capacitance value required is dependent upon the load current, output voltage for the adjustable regulator, and the type of capacitor selected. The least stable condition is encountered at maximum load current and minimum output voltage. Figure 22 shows that for operation in the “Stable” region, under the conditions specified, the magnitude of the output capacitor impedance |ZO| must not exceed 0.4 .
This limit must be observed over the entire operating temperature range of the regulator circuit. With economical electrolytic capacitors, cold temperature operation can pose a serious stability problem. As the electrolyte freezes, around −30°C, the capacitance will decrease and the equivalent series resistance (ESR) will increase drastically, causing the circuit to oscillate. Quality electrolytic capacitors with extended temperature ranges of −40° to +85°C and −55° to +105°C are readily available. Solid tantalum capacitors may be a better choice if small size is a requirement, however, the maximum ⏐ZO⏐ limit over temperature must be observed. Note that in the stable region, the output noise voltage is linearly proportional to ⏐ZO⏐. In effect, CO dictates the high frequency roll−off point of the circuit. Operation in the area titled “Marginally Stable” will cause the output of the regulator to exhibit random bursts of oscillation that decay in an under−damped fashion. Continuous oscillation occurs when operating in the area titled “Unstable”. It is suggested that oven testing of the entire circuit be performed with maximum load, minimum input voltage, and minimum ambient temperature.
