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UC3172ADW датащи(PDF) 10 Page - Texas Instruments |
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UC3172ADW датащи(HTML) 10 Page - Texas Instruments |
10 / 12 page (10) R3 = R4 UV1 1.3 − 1 , and R5 = R6 UV2 1.3 − 1 During park, supply to the load, and the UC3172A, is typically recovered from the back EMF of the spindle mo- tor. When the supply voltage at the VL supply pin drops below the UVLO voltage, (2.4V high-to-low), the output of the A amplifier is forced high, over-riding the programmed park voltage. The UC3172A will maintain drive to the load down to low supply levels. For example, with 1.5 volts of recovered back EMF, the UC3172A can still de- liver 50mA of drive to a 10 Ω load. Parking With Very Low Back EMF The UC3172A can also be configured to get parking drive to the load with very low recovered back EMF. Figure 3 il- lustrates how the PWROK pin can be used to drive an external PNP device to achieve very low parking drive Vsat losses. With this configuration, the UC3172A will be able to force approximately one volt across the load with a recovered back EMF voltage of 1.3V. During system commanded parking with the supplies present, the VPARK pin is still used to set the maximum voltage to the load. The logic function of the PWROK pin is still available since the external PNP will provide isola- tion to this output when it is high. Base drive to the PRKDRV and PWROK pins are pro- vided by the VL supply pin. By using a hold up capacitor, CHOLD, the drive can be maintained to the load as the back EMF drops to below 1 volt. A variation on this ap- proach is to add a connection between the VL pin and the recovered back EMF, this will eliminate the need for the holdup capacitor and provide operation down to about 1.2V of back EMF recovery. Care with this ap- proach should be taken in case the 5V supply hangs at just below the programmed UV threshold. In this situation large currents could flow from this supply through the ex- ternal PNP and into the A output which, until the supply UC3172A APPLICATION INFORMATION (cont.) Figure 2. Controlled Velocity Head Parking UDG-94042 10 |
Аналогичный номер детали - UC3172ADW |
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Аналогичное описание - UC3172ADW |
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