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AMS1086CM-1.8 Datasheet(PDF) 4 Page - Advanced Monolithic Systems |
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AMS1086CM-1.8 Datasheet(HTML) 4 Page - Advanced Monolithic Systems |
4 / 8 page Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS1086 APPLICATION HINTS The AMS1086 series of adjustable and fixed regulators are easy to use and have all the protection features expected in high performance voltage regulators: short circuit protection and thermal shutdown. Pin compatible with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage, more precise reference tolerance and improved reference stability with temperature. Stability The circuit design used in the AMS1086 series requires the use of a 10 µF output capacitor as part of the device frequency compensation. If the output voltage is set for 3.0V or higher, AMS1086 will operate with an output capacitor as low as 1 µF tantalum or 3.3 µF electrolytic and C ADJ as low as 0.5µF. For output voltages lower than 3.0V, CADJ capacitor value should be minimum 1 µF to ensure stability. To improve stability and transient response, larger values of output capacitor can be used. Protection Diodes Unlike older regulators, the AMS1086 family does not need any protection diodes between the adjustment pin and the output and from the output to the input to prevent over-stressing the die. Internal resistors are limiting the internal current paths on the AMS1086 adjustment pin, therefore even with capacitors on the adjustment pin no protection diode is needed to ensure device safety under short-circuit conditions. Diodes between the input and output are not usually needed. Microsecond surge currents of 50A to 100A can be handled by the internal diode between the input and output pins of the device. In normal operations it is difficult to get those values of surge currents even with the use of large output capacitances. If high value output capacitors are used, such as 1000 µF to 5000µF and the input pin is instantaneously shorted to ground, damage can occur. A diode from output to input is recommended, when a crowbar circuit at the input of the AMS1086 is used. Normal power supply cycling or even plugging and unplugging in the system will not generate current large enough to do any damage. The adjustment pin can be driven on a transient basis ±25V, with respect to the output without any device degradation. As with any IC regulator, none the protection circuitry will be functional and the internal transistors will break down if the maximum input to output voltage differential is exceeded. AMS1086 IN OUT ADJ + C OUT 10 µF V OUT R 1 R 2 C ADJ 1 µF D1 V IN Overload Recovery When the power is first turned on, as the input voltage rises, the output follows the input, permitting the regulator to start up into heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential remains small, allowing the regulator to supply large output currents. A problem can occur with a heavy output load when the input voltage is high and the output voltage is low, when the removal of an output short will not permit the output voltage to recover. The load line for such a load may intersect two points on the output current curve. In this case, there are two stable output operating points for the regulator. With this double intersection, the power supply may need to be cycled down to zero and brought up again to make the output recover. Ripple Rejection The ripple rejection values are measured with the adjustment pin bypassed. The impedance of the adjust pin capacitor at the ripple frequency should be less than the value of R1 (normally 100 Ω to120 Ω) for a proper bypassing and ripple rejection approaching the values shown. The size of the required adjust pin capacitor is a function of the input ripple frequency. If R1=100 Ω at 120Hz the adjust pin capacitor should be 25 µF. At 10kHz only 0.22µF is needed. The ripple rejection will be a function of output voltage, in circuits without an adjust pin bypass capacitor. The output ripple will increase directly as a ratio of the output voltage to the reference voltage (VOUT / VREF). Output Voltage The AMS1086 series develops a 1.25V reference voltage between the output and the adjust terminal. Placing a resistor between these two terminals causes a constant current to flow through R1 and down through R2 to set the overall output voltage. |
Similar Part No. - AMS1086CM-1.8 |
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Similar Description - AMS1086CM-1.8 |
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