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NCV8674DS120R4G Datasheet(PDF) 9 Page - ON Semiconductor |
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NCV8674DS120R4G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 11 page NCV8674 http://onsemi.com 9 Circuit Description The NCV8674 is a precision trimmed 5.0 V or 12 V fixed output regulator. Careful management of light load consumption combined with a low leakage process results in a typical quiescent current of 30 mA. The device has current capability of 350 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 NCV8674 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. Stability is guaranteed at values COUT ≥ 22 mF and ESR ≤ 7.0 W, within the operating temperature range. Actual limits are shown in a graph in the Typical Characteristics section. Calculating Power Dissipation in a Single Output Linear Regulator The maximum power dissipation for a single output regulator (Figure 2) is: IOUT(max) ) VIN(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, IOUT(max) is the maximum output current for the application, and Iq is the quiescent current the regulator consumes at IOUT(max). Once the value of PD(Max) is known, the maximum permissible value of RqJA can be calculated: RqJA + 150oC * TA PD (eq. 2) The value of RqJA can then be compared with those in thermal resistance versus copper area graph (Figure 26). Those designs with cooling area corresponding to RqJA’s less than the calculated value in Equation 2 will keep the die temperature below 150 °C. The current flow and voltages are shown in the Measurement Circuit Diagram. 0 25 50 75 0 100 200 300 400 500 600 700 800 900 COPPER AREA (mm2) Figure 26. D2PAK 1 oz D2PAK 2 oz 0.1 1 10 100 0.000001 0.0001 0.01 1 100 0 100 200 300 400 500 600 700 800 900 PULSE TIME (sec) Figure 27. NCV8674 @ PCB Cu Area 650 mm2 PCB Cu thk 1 oz D2PAK Single Pulse 10 0.1 1000 |
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