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ADP3309ART-2.5-RL7 bảng dữ liệu(PDF) 10 Page - Analog Devices |
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ADP3309ART-2.5-RL7 bảng dữ liệu(HTML) 10 Page - Analog Devices |
10 / 12 page ADP3309 Rev. C | Page 10 of 12 APPLICATION INFORMATION CAPACITOR SELECTION: anyCAP Output Capacitors: As with any micropower device, output transient response is a function of the output capacitance. The ADP3309 is stable with a wide range of capacitor values, types, and ESR (anyCAP). A capacitor as low as 0.47 μF is all that is needed for stability. However, larger capacitors can be used if high output current surges are anticipated. The ADP3309 is stable with extremely low ESR capacitors (ESR ≈ 0), such as multilayer ceramic capacitors (MLCC) or OSCON. Input Bypass Capacitor: An input bypass capacitor is not required. However, for applications where the input source is high impedance or far from the input pin, a bypass capacitor is recommended. Connecting a 0.47 μF capacitor from the input pin (Pin 1) to ground reduces the circuit’s sensitivity to PC board layout. If a bigger output capacitor is used, the input capacitor must be 1 μF minimum. THERMAL OVERLOAD PROTECTION The ADP3309 is protected against damage due to excessive power dissipation by its thermal overload protection circuit, which limits the die temperature to a maximum of 165°C. Under extreme conditions (that is, high ambient temperature and power dissipation) where die temperature starts to rise above 165°C, the output current is reduced until the die temperature has dropped to a safe level. The output current is restored when the die temperature is reduced. Current and thermal limit protections are intended to protect the device against accidental overload conditions. For normal operation, device power dissipation should be externally limited so that junction temperatures do not exceed 125°C. CALCULATING JUNCTION TEMPERATURE Device power dissipation is calculated as follows: PD = (VIN – VOUT) ILOAD + (VIN) IGND where: ILOAD is the load current. IGND is the ground current. VIN is the input voltage. VOUT is the output voltage. Assuming ILOAD = 100 mA, IGND = 2 mA, VIN = 5.0 V, and VOUT = 3.3 V, device power dissipation is PD = (5.0 − 3.3) 100 mA + 5.0 × 2 mA = 180 mW ΔT = TJ – TA = PD × θJA = 0.18 × 190 = 34.2°C With a maximum junction temperature of 125°C, this yields a maximum ambient temperature of ~90°C. PRINTED CIRCUIT BOARD LAYOUT CONSIDERATION Surface-mount components rely on the conductive traces or pads to transfer heat away from the device. Appropriate PC board layout techniques should be used to remove heat from the immediate vicinity of the package. The following general guidelines will be helpful when designing a board layout: 1. PC board traces with larger cross section areas remove more heat. For optimum results, use PC boards with thicker copper and/or wider traces. 2. Increase the surface area exposed to open air so heat can be removed by convection or forced air flow. 3. Do not use solder mask or silk screen on the heat dissipating traces because it increases the junction to ambient thermal resistance of the package. SHUTDOWN MODE Applying a TTL high signal to the shutdown pin or tying it to the input pin turns the output on. Pulling the shutdown pin down to a TTL low signal or tying it to ground turns the output off. In shutdown mode, quiescent current is reduced to less than 1 μA. ERROR FLAG DROPOUT DETECTOR The ADP3309 maintains its output voltage over a wide range of load, input voltage, and temperature conditions. If the output is about to lose regulation, for example, by reducing the supply voltage below the combined regulated output and dropout voltages, the ERR pin will be activated. The ERR output is an open collector that will be driven low. Once set, the ERR or flag’s hysteresis keeps the output low until a small margin of operating range is restored either by raising the supply voltage or reducing the load. |
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