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AMS2502CS-18 Datasheet(PDF) 4 Page - Advanced Monolithic Systems |
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AMS2502CS-18 Datasheet(HTML) 4 Page - Advanced Monolithic Systems |
4 / 8 page Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140 AMS2501/AMS2502 APPLICATION HINTS The AMS2501/AMS2502 series of adjustable and fixed regulators is designed to make use of multiple power supplies, existing in most systems, to reduce the dropout voltage. One of the advantages of the two supply approach is maximizing the efficiency. The second supply is at least 1.2V greater than output voltage and is providing the power for the control circuitry and supplies the drive current to the NPN output transistor. This allows the NPN to be driven into saturation; thereby reducing the dropout voltage by a VBE compared to conventional designs. For the control voltage the current requirement is small, equal to about 1% of the output current or approximately 10mA for a 1A load. Most of this current is drive current for the NPN output transistor. This drive current becomes part of the output current. The maximum voltage on the Control pin is 13V. The maximum voltage at the Power pin is 7V. Ground pin current for fixed voltage devices is typical 6mA and is constant as a function of load. Adjust pin current for adjustable devices is 40 µA at 25°C and varies proportional to absolute temperature. The improved frequency compensation of AMS2501/AMS2502 permits the use of capacitors with very low ESR. Output voltage tolerances are tighter and include transient response as part of the specification. Designed to meet the fast current load step, the AMS2501/AMS2502 also saves total cost by needing less output capacitance to maintain regulation. Careful design of the AMS2501/AMS2502 has eliminated any supply sequencing issues associated with a dual supply system. The output voltage will not turn on until both supplies are operating. If the control voltage comes up first, the output current will be limited to a few milliamperes until the power input voltage comes up. If power input comes up first the output will not turn on at all until the control voltage comes up. The output can never come up unregulated. By tying the control and power inputs together the AMS2501/AMS2502 can also be operated as a single supply device. In single supply operation the dropout will be determined by the minimum control voltage. Both the fixed and adjustable versions have remote sense pins, permitting very accurate regulation of output voltage at the load, rather than at the regulator. As a result, over an output current range of 100mA to 1A with a 2.5V output, the typical load regulation is less than 1mV. For AMS2502 the reference voltage is brought out to pin 7, allowing the user to improve transient response by bypassing the internal resistor divider. Optimum transient response is provided using a capacitor in the range of 0.1 µF to 1µF for bypassing the Reference pin. The value chosen will depend on the amount of output capacitance in the system. This devices can hold 1% accuracy over the full temperature range and load current range, guaranteed, when combined with ratiometrically accurate internal divider resistors and operating with an input/output differential of well under 1V. Typical applications for the AMS2501/AMS2502 include 3.3V to 2.5V conversion with a 5V control supply, 5V to 4.2V conversion with a 12V control supply or 5V to 3.6V conversion with a 12V control supply. Capable of 1A of output current with a maximum dropout of 0.8V the AMS2501/AMS2502 also has a fast transient response that allows it to handle large current changes. The device is fully protected against overcurrent and overtemperature conditions. Grounding and Output Sensing The AMS2501/AMS2502 allows true Kelvin sensing for both the high and low side of the load. As a result the voltage regulation at he load can be easily optimized. Voltage drops due to parasitic resistances between the regulator and the load can be placed inside the regulation loop of the AMS2501/AMS2502. The advantages of remote sensing are illustrated in figures 1 through 3. Figure 1 shows the device connected as a conventional 3 terminal regulator with the Sense lead connected directly to the output of the device. RP is the parasitic resistance of the connections between the device and the load. RP is made up of the PCB traces and /or connector resistances (in the case of a modular regulator) between the regulator and the load. Trace A of figure 3 illustrates the effect of RP. Very small resistances cause significant load regulation steps. Figure 2 shows the device connected to take advantage of the remote sense feature. The Sense pin and the top of the resistor divider are connected to the top of the load; the bottom of the resistor divider is connected to the bottom of the load. RP is now connected inside the regulation loop of the AMS2501/AMS2502 and for reasonable values of RP the load regulation at the load will be negligible. The effect on output regulation can be seen in trace B of figure 3. CONTROL POWER SENSE AMS2501 OUTPUT ADJ LOAD + - V OUT R P R P R1 R2 5V 3.3V Figure 1. Conventional Load Sensing |
Similar Part No. - AMS2502CS-18 |
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Similar Description - AMS2502CS-18 |
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