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CS5253-1GDPR5G Datenblatt(PDF) 8 Page - ON Semiconductor |
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CS5253-1GDPR5G Datenblatt(HTML) 8 Page - ON Semiconductor |
8 / 10 page CS5253−1 http://onsemi.com 8 Figure 20. This Circuit Is an Example of How the CS5253−1 Can Be Short−Circuit Protected When Operating With VOUT > 6.0 V VCONTROL VPOWER VSENSE VOUT VADJ External Supply External Supply CS5253−1 Stability Considerations The output compensation capacitor helps determine three main characteristics of a linear regulator: loop stability, startup delay, and load transient response. Different capacitor types vary widely in tolerance, Equivalent Series Resistance (ESR), Equivalent Series Inductance (ESI), and variation over temperature. Tantalum and aluminum electrolytic capacitors work best, with electrolytic capacitors being less expensive in general, but varying more in capacitor value and ESR over temperature. The CS5253−1 requires an output capacitor to guarantee loop stability. The Stability vs ESR graph in the typical performance section shows the minimum ESR needed to guarantee stability, but under ideal conditions. These include: having VOUT connected to VSENSE directly at the IC pins; the compensation capacitor located right at the pins with a minimum lead length; the adjust feedback resistor divider ground, (bottom of R2 in Figure 19), connected right at the capacitor ground; and with power supply decoupling capacitors located close to the IC pins. The actual performance will vary greatly with board layout for each application. In particular, the use of the remote sensing feature will require a larger capacitor with less ESR. For most applications, a minimum of 33 mF tantalum or 150 mF aluminum electrolytic, with an ESR less than 1.0 W over temperature, is recommended. Larger capacitors and lower ESR will improve stability. The load transient response, during the time it takes the regulator to respond, is also determined by the output capacitor. For large changes in load current, the ESR of the output capacitor causes an immediate drop in output voltage given by: DV + DI ESR There is then an additional drop in output voltage given by: DV + DI T C where T is the time for the regulation loop to begin to respond. The very fast transient response time of the CS5253−1 allows the ESR effect to dominate. 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 transient response. 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 VCONTROL drops. In the CS5253−1 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 21 is recommended. Figure 21. Diode Protection Circuit CS5253−1 VCONTROL VPOWER VOUT VSENSE Adjust A rule of thumb useful in determining if a protection diode is required is to solve for current: I + C V T where: I is the current flow out of the load capacitance when VCONTROL is shorted, C is the value of load capacitance V is the output voltage, and T is the time duration required for VCONTROL to transition from high to being shorted. If the calculated current is greater than or equal to the typical short circuit current value provided in the specifications, serious thought should be given to the use of a protection diode. |
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Ähnliche Beschreibung - CS5253-1GDPR5G |
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