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CS5207-1 Datasheet(PDF) 4 Page - ON Semiconductor |
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CS5207-1 Datasheet(HTML) 4 Page - ON Semiconductor |
4 / 7 page CS5207−1 http://onsemi.com 4 APPLICATIONS INFORMATION The CS5207−1 linear regulator provides adjustable voltages at currents up to 7.0 A. The regulator is protected against short circuit, and includes thermal shutdown and safe area protection (SOA) circuitry. The SOA protection circuitry decreases the maximum available output current as the input−output differential voltage increases. The CS5207−1 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. Adjustable Operation The adjustable regulator has an output voltage range of 1.25 V to 13 V. An external resistor divider sets the output voltage as shown in Figure 7. 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 current to flow to ground. This current creates a voltage across R2 that adds to the 1.25 V across R1 and sets the overall output voltage. The adjust pin current (typically 50 μA) 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 R1 ) R2 R1 ) 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 10 mA. R1 and R2 should be the same type, e.g. metal film for best tracking over temperature. The adjust pin is bypassed to improve the transient response and ripple rejection of the regulator. Figure 7. Resistor Divider Scheme for the Adjustable Version VIN CS5207−1 VOUT Adj VREF R1 R2 VOUT VIN C1 C2 CAdj IAdj Stability Considerations 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 electrolytic capacitor is best, since a film or ceramic capacitor with almost zero ESR can cause instability. The aluminum electrolytic capacitor is the least expensive solution. However, when the circuit operates at low temperatures, both the value and ESR of the capacitor will vary considerably. The capacitor manufacturer’s data sheet provides this information. A 22 μF tantalum capacitor will work for most applications, but with high current regulators such as the CS5207−1 the transient response and stability improve with higher values of capacitor. The majority of applications for this regulator involve large changes in load current so the output capacitor must supply the instantaneous load current. The ESR of the output capacitor causes an immediate drop in output voltage given by: DV + DI ESR For microprocessor applications it is customary to use an output capacitor network consisting of several tantalum and ceramic capacitors in parallel. This reduces the overall ESR and reduces the instantaneous output voltage drop under transient load conditions. The output capacitor network should be as close to the load as possible for the best results. Protection Diodes When large external capacitors are used with a linear regulator it is sometimes necessary to add protection diodes. If the input voltage of the regulator gets shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage and the rate at which VIN drops. In the CS5207−1 linear regulator, the discharge path is through a large junction and protection diodes are not usually needed. If the regulator is used with large values of output capacitance and the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown in Figure 8 is recommended. Figure 8. Protection Diode Scheme for Adjustable Output Regulator VIN CS5207−1 VOUT Adj R1 R2 VOUT VIN C1 C2 CAdj IN4002 (Optional) |
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