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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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CS5203-1GDP3 Fiches technique(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS5203-1GDP3 Fiches technique(HTML) 5 Page - Cherry Semiconductor Corporation |
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5 / 8 page  5 Applications Information The CS5203-1 linear regulator provides adjustable volt- ages at currents up to 3A. The regulator is protected against overcurrent conditions and includes thermal shutdown. The CS5203-1 has a composite PNP-NPN output transistor and requires an output capacitor for stability. A detailed procedure for selecting this capacitor is included in the Stability Considerations section. The CS5203-1 has an output voltage range of 1.25V to 5.5V. An external resistor divider sets the output voltage as shown in Figure 1. The regulator maintains a fixed 1.25V (typical) reference between the output pin and the adjust pin. A resistor divider network R1 and R2 causes a fixed cur- rent to flow to ground. This current creates a voltage across R2 that adds to the 1.25V across R1 and sets the overall output voltage. The adjust pin current (typically 50µA) also flows through R2 and adds a small error that should be taken into account if precise adjustment of VOUT is necessary. The output voltage is set according to the formula: VOUT = VREF ´ () + IAdj ´ R2 The term IAdj ´ R2 represents the error added by the adjust pin current. R1 is chosen so that the minimum load current is at least 2mA. R1 and R2 should be the same type, e.g. metal film for best tracking over temperature. While not required, a bypass capacitor between the adjust pin and ground will improve ripple rejection and transient response. A 0.1µF tantalum capacitor is recommended for Òfirst cutÓ design. Type and value may then be varied to optimize perfor- mance vs. price. Figure 1. Resistor divider scheme. The 5203-1 linear regulator has an absolute maximum specification of 7V for the voltage difference between VIN and VOUT. However, the IC may be used to regulate volt- ages in excess of 7V. The main considerations in such a design are power-up and short circuit capability. In most applications, ramp-up of the power supply to VIN is fairly slow, typically on the order of several tens of mil- liseconds, while the regulator responds in less than one microsecond. In this case, the linear regulator begins charging the load as soon as the VIN to VOUT differential is large enough that the pass transistor conducts current. The load at this point is essentially at ground, and the supply voltage is on the order of several hundred millivolts, with the result that the pass transistor is in dropout. As the sup- ply to VIN increases, the pass transistor will remain in dropout, and current is passed to the load until VOUT reaches the point at which the IC is in regulation. Further increase in the supply voltage brings the pass transistor out of dropout. The result is that the output voltage fol- lows the power supply ramp-up, staying in dropout until the regulation point is reached. In this manner, any output voltage may be regulated. There is no theoretical limit to the regulated voltage as long as the VIN to VOUT differen- tial of 7V is not exceeded. However, the possibility of destroying the IC in a short circuit condition is very real for this type of design. Short circuit conditions will result in the immediate operation of the pass transistor outside of its safe operating area. Over- voltage stresses will then cause destruction of the pass transistor before overcurrent or thermal shutdown circuit- ry can become active. Additional circuitry may be required to clamp the VIN to VOUT differential to less than 7V if fail- safe operation is required. One possible clamp circuit is illustrated in figure 2; however, the design of clamp cir- cuitry must be done on an application by application basis. Care must be taken to ensure the clamp actually protects the design. Components used in the clamp design must be able to withstand the short circuit condition indefinitely while protecting the IC. Figure 2. Short Circuit Protection Circuit for High Voltage Application. The output or compensation capacitor helps determine three main characteristics of a linear regulator: start-up delay, load transient response and loop stability. The capacitor value and type is based on cost, availability, size and temperature constraints. A tantalum or aluminum Stability Considerations VIN VOUT VAdj EXTERNAL SUPPLY VOUT VOUT VIN CS5203-1 VIN Adj R1 R2 C1 CAdj VOUT C2 VREF IAdj R1 + R2 R1 Adjustable Operation |
Numéro de pièce similaire - CS5203-1GDP3 |
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Description similaire - CS5203-1GDP3 |
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