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NCV8664C Folha de dados(PDF) 9 Page - ON Semiconductor |
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NCV8664C Folha de dados(HTML) 9 Page - ON Semiconductor |
9 / 13 page NCV8664C www.onsemi.com 9 Circuit Description The NCV8664C is a precision trimmed 3.3 V and 5.0 V fixed output regulator. Careful management of light load consumption combined with a low leakage process results in a typical quiescent current of 22 mA. The device has current capability of 150 mA, with 600 mV of dropout voltage at full rated load current. The regulation is provided by a PNP pass transistor controlled by an error amplifier with a bandgap reference. The regulator is protected by both current limit and short circuit protection. Thermal shutdown occurs above 150 °C to protect the IC during overloads and extreme ambient temperatures. Regulator The error amplifier compares the reference voltage to a sample of the output voltage (Vout) and drives the base of a PNP series pass transistor by a buffer. The reference is a bandgap design to give it a temperature−stable output. Saturation control of the PNP is a function of the load current and input voltage. Over saturation of the output power device is prevented, and quiescent current in the ground pin is minimized. The NCV8664C is equipped with foldback current protection. This protection is designed to reduce the current limit during an overcurrent situation. Regulator Stability Considerations The input capacitor CIN in Figure 2 is necessary for compensating input line reactance. Possible oscillations caused by input inductance and input capacitance can be damped by using a resistor of approximately 1 W in series with CIN. The output or compensation capacitor, COUT helps determine three main characteristics of a linear regulator: startup delay, load transient response and loop stability. The capacitor value and type should be based on cost, availability, size and temperature constraints. Tantalum, aluminum electrolytic, film, or ceramic capacitors are all acceptable solutions, however, attention must be paid to ESR constraints. The aluminum electrolytic capacitor is the least expensive solution, but, if the circuit operates at low temperatures (−25 °C to −40°C), both the value and ESR of the capacitor will vary considerably. The capacitor manufacturer’s data sheet usually provides this information. The value for the output capacitor COUT shown in Figure 2 should work for most applications; however, it is not necessarily the optimized solution. Actual Stability Regions are shown in the graphs in the Typical Performance Characteristics section. Calculating Power Dissipation in a Single Output Linear Regulator The maximum power dissipation for a single output regulator (Figure 3) is: IQ(max) ) VI(max) @ Iq (eq. 1) PD(max) + [VIN(max) * VOUT(min)] @ Where: VIN(max) is the maximum input voltage, VOUT(min) is the minimum output voltage, IQ(max) is the maximum output current for the application, and Iq is the quiescent current the regulator consumes at IQ(max). Once the value of PD(Max) is known, the maximum permissible value of RqJA can be calculated: P qJA + 150oC * TA PD (eq. 2) The value of RqJA can then be compared with those in the package section of the data sheet. Those packages with RqJA’s less than the calculated value in Equation 2 will keep the die temperature below 150 °C. In some cases, none of the packages will be sufficient to dissipate the heat generated by the IC, and an external heat sink will be required. The current flow and voltages are shown in the Measurement Circuit Diagram. Heat Sinks A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air. Each material in the heat flow path between the IC and the outside environment will have a thermal resistance. Like series electrical resistances, these resistances are summed to determine the value of RqJA: R qJA + RqJC ) RqCS ) RqSA (eq. 3) Where: RqJC = the junction−to−case thermal resistance, RqCS = the case−to−heat sink thermal resistance, and RqSA = the heat sink−to−ambient thermal resistance. RqJC appears in the package section of the data sheet. Like RqJA, it too is a function of package type. RqCS and RqSA are functions of the package type, heatsink and the interface between them. These values appear in data sheets of heatsink manufacturers. Thermal, mounting, and heat sinking are discussed in the ON Semiconductor application note AN1040/D, available on the ON Semiconductor Website. |
Nº de peça semelhante - NCV8664C_17 |
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Descrição semelhante - NCV8664C_17 |
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