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ADP3000AR-33 Datasheet(PDF) 8 Page - Analog Devices |
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ADP3000AR-33 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page ADP3000 –8– REV. 0 The circuit of Figure 18 may produce multiple pulses when approaching the trip point due to noise coupled into the SET input. To prevent multiple interrupts to the digital logic, hysteresis can be added to the circuit (Figure 18). Resistor R HYS, with a value of 1 M Ω to 10 MΩ, provides the hysteresis. The addition of R HYS will change the trip point slightly, so the new value for R1 will be: R1 = V LOBATT –1.245V 1.245V R2 − V L −1.245V RL + RHYS where VL is the logic power supply voltage, RL is the pull-up resistor, and RHYS creates the hysteresis. POWER TRANSISTOR PROTECTION DIODE IN STEP- DOWN CONFIGURATION When operating the ADP3000 in the step-down mode, the output voltage is impressed across the internal power switch’s emitter-base junction when the switch is off. In order to protect the switch, a Schottky diode must be placed in a series with SW2 when the output voltage is set to higher than 6 V. Figure 19 shows the proper way to place the protection diode, D2. The selection of this diode is identical to the step-down commut- ing diode (see Diode Selection section for information). ILIM VIN SW1 FB SW2 GND ADP3000 C2 R3 VIN 4 1 2 3 8 5 + L1 R1 R2 D2 VOUT > 6V + D1 D1, D2 = 1N5818 SCHOTTKY DIODES C1 Figure 19. Step-Down Model VOUT > 6.0 V THERMAL CONSIDERATIONS Power dissipation internal to the ADP3000 can be approximated with the following equations. Step-Up PD = ISW 2 R + V IN ISW β D 1– V IN VO 4IO ISW + IQ [] V IN [] where: ISW is ILIMIT in the case of current limit programmed externally, or maximum inductor current in the case of current limit not programmed externally. R = 1 Ω (Typical R CE(SAT)). D = 0.75 (Typical Duty Ratio for a Single Switching Cycle). VO = Output Voltage. IO = Output Current. VIN = Input Voltage. IQ = 500 µA (Typical Shutdown Quiescent Current). β = 30 (Typical Forced Beta) Step-Down PD = ISW VCESAT 1+ 1 β VO VIN – VCE SAT () 2 IO ISW + IQ [] V IN [] where: ISW is ILIMIT in the case of current limit is programmed externally or maximum inductor current in the case of current limit is not programmed eternally. VCE(SAT) = Check this value by applying ISW to Figure 8b. 1.2 V is typical value. D = 0.75 (Typical Duty Ratio for a Single Switching Cycle). VO = Output Voltage. IO = Output Current. VIN = Input Voltage. IQ = 500 µA (Typical Shutdown Quiescent Current). β = 30 (Typical Forced Beta). The temperature rise can be calculated from: ∆T = P D ×θ JA where: ∆T = Temperature Rise. PD = Device Power Dissipation. θ JA = Thermal Resistance (Junction-to-Ambient). As example, consider a boost converter with the following specifications: VIN = 2 V, IO = 180 mA, VO = 3.3 V. ISW = 0.8 A (Externally Programmed). With Step-Up Power Dissipation Equation: PD = 0.82 × 1+ (2)(0.8) 30 0.75 [] 1– 2 3.3 (4) 0.18 0.8 + 500E − 6 [] 2[] = 185 mW Using the SO-8 Package: ∆T = 185 mW (170°C/W) = 31.5°C. Using the N-8 Package: ∆T = 185 mW (120°C/W) = 22.2°C. At a 70 °C ambient, die temperature would be 101.45°C for SO-8 package and 92.2 °C for N-8 package. These junction temperatures are well below the maximum recommended junction temperature of 125 °C. Finally, the die temperature can be decreased up to 20% by using a large metal ground plate as ground pickup for the ADP3000. |
Similar Part No. - ADP3000AR-33 |
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Similar Description - ADP3000AR-33 |
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