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| Regulator ICs Step-down type switching power supply under BA9771T development The BA9771T step-down type switching power supply accepts a maximum input voltage of 46V, and can output a maximum current of 1.5A. The output voltage can be set from 5 to 40V using external resistors. FApplications Printers and car stereos FFeatures 1) Output voltage can be set from 5V (Vref) to 40V. 2) Output current capacity is 1.5A. 3) Output current limiter circuit on the chip prevents the chip from destruction in the case of a short circuit in the output. 4) A temperature protection circuit protects the IC from destruction due to heat generated by excessive loads. FAbsolute maximum ratings (Ta = 25_C) 5) Ideal as a power supply for printers. 6) TO220FP-5 package is perfect for compact designs. 398 Regulator ICs FBlock diagram BA9771T 399 Regulator ICs FInput / output circuits BA9771T 400 Regulator ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C, Vi = 35V, Vo = Vref) BA9771T 401 Regulator ICs FMeasurement circuits BA9771T 402 Regulator ICs BA9771T 403 Regulator ICs FApplication example BA9771T 404 Regulator ICs FOperation notes (1) The over-current protection circuit and short circuit protection limit the current to a maximum of 2.5A (Typ.). When the pin 5 voltage is clamped to a voltage above 0.4V, the 2.5A current is internally set to a duty cycle about 10% to protect the IC. However, in this case, it is normal for the coil current to be 2.5A, so even if it is possible to clamp the pin 5 voltage to a voltage above 0.4V, you should confirm that there are no problems with the overall set. In addition to the above operation, if you lower the pin 5 voltage to below 0.4V, the circuit will interpret this as an output short circuit, and in addition to applying a current limit of 0.5A (Typ.), the pin 4 output will be switched on and off repeatedly with a duty cycle about 10% in the same way as for when the pin 5 voltage was over 0.4V (see the diagram below). BA9771T However, to ensure that the short circuit protection operates correctly, we recommend that you connect a 15k resister and 330nF capacitor in series with the FC pin (pin 1), as shown in Fig. 6. If there is no problem with the basic circuit operation, the resistor connected to pin 1 can be made lower than 15k, but if it is made larger than 15k, the short circuit current will become larger than 1A, so care is required. For the capacitor, if a component with a value larger than 330nF is not used, the short circuit current may become greater than 1A. (2) Rising and falling characteristics The output voltage has hysteresis, and begins to rise when the power supply voltage is 8V, and fall when the power supply voltage is 3V. The hysteresis is determined by a resister and a diode, and has a temperature derating of -30mV / _C. 405 Regulator ICs FElectrical characteristics curves BA9771T FExternal dimensions (Units: mm) 406 |
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