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GM317TC3R Datasheet(PDF) 5 Page - Gamma Microelectronics Inc. |
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GM317TC3R Datasheet(HTML) 5 Page - Gamma Microelectronics Inc. |
5 / 9 page 5 GM317 3-TERMINAL 1.5A ADJUSTABLE REGULATOR VIN VOUT VREF R1 R2 IPROG IADJ GM317 Adjust VREF = 1.25V typical Basic Circuit Configuration VIN VOUT GM317 Adjust R1 R2 D2 1N4002 D1 1N4002 CO CADJ CIN Application Information Basic Circuit Operation The GM317 is a 3- terminal floating regulator. In operation, the GM317 develops and maintains a nominal 1.25V reference (VREF) between its output and adjustment terminals. This reference voltage is converted to a programming current flow through R2 to ground. The regulated output voltage is given by: Since the current from the adjustment terminal (IADJ) represents an error term in the equation, the GM317was designed to control IADJ to less than 100µA and keep it constant. To do this, all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. Since the GM317 is a floating regulator, it is only the voltage differential across the circuit which is important to performance, and operation at high voltages with respect to ground is possible. Load Regulation The GM317 is capable of providing extremely good load regulation, but a few precautions are needed to obtain maximum performance. For best performance, the programming resistor R1 should be connected as close to the regulator as possible to minimize line drops which effectively appear in series with the reference, thereby degrading regulation. The ground end of R2 can be returned near the load ground to provide remote ground sensing and improve load regulation. External Capacitors A 0.1µF disc or 1.0µF tantalum input bypass capacitor CIN is recommended to reduce the sensitivity to input line impedance. The adjustment terminal may be bypassed to ground to improve ripple rejection. This capacitor CADJ prevents ripple from being amplified as the output voltage is increased. A 10µF capacitor should improve ripple rejection about 15 dB at 120Hz in a 10V application. Although the GM317 is stable with no output capacitance, like any feedback circuit, certain values of external capacitance can cause excessive ringing. An output capacitance CO in the form of a 1.0µF tantalum or 25µF aluminum electrolytic capacitor on the output swamps this effect and insures stability. Protection Diodes When external capacitors are used with any IC regulator, it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. The figure below shows the GM317 with the recommended protection diodes for output for output voltage in excess of 25V or high capacitance values (CO > 25µF, CADJ > 10µF). Diode D1 prevents CO from discharging thru the IC during an input short circuit. Diode D2 protects against capacitor CADJ discharging through the IC during an output short circuit. The combination of diodes D1 and D2 prevents CADJ from discharging through the IC during an input short circuit. VOUT = VREF (1 + R1 ) + IADJ R2 R2 |
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