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UC3173A датащи(PDF) 10 Page - Texas Instruments |
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UC3173A датащи(HTML) 10 Page - Texas Instruments |
10 / 12 page 10 UC3173A Head Parking In Fig. 2, the UC3173A is shown configured to force a programmed voltage at the A amplifier output upon the activation of a park condition. A pair of feedback resistors R1 and R2 set this voltage as defined by: R1 = R2 VPARK 1.3 –1 (10) R2 is typically chosen in the range of 10k Ω to 100kΩ. The B amplifier output is tri-stated during park, this side of the load is driven low by the PRKDRV pin. A series re- sistor, RP in the figure, can be inserted in series with the load to limit the peak current if required. The UV thresholds for the supply monitors are set by picking R4 and R6 values in the 10k Ω to 100kΩ range and then calculating R3 and R5 according to: R3 = R4 UV1 1.3 – 1 , and R5 = R6 UV2 1.3 –1 (11) During park, supply to the load, and the UC3173A, is typically recovered from the back EMF of the spindle motor. When the supply voltage at the VL supply pin drops below the UVLO voltage, (2.3V high-to-low), the output of the A amplifier is forced high, over-riding the programmed park voltage. The UC3173A will maintain drive to the load down to low supply levels. For example, with 1.5 volts of recovered back EMF, the UC3173A can still deliver 50mA of drive to a 10 Ω load. Parking With Very Low Back EMF The UC3173A can also be configured to get parking drive to the load with very low recovered back EMF. Fig. 3 illustrates 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 UC3173A 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 1V. 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 situa- tion large currents could flow from this supply through the external PNP and into the A output which, until the supply drops below a certain level, is forcing a pro- grammed voltage. APPLICATION INFORMATION (cont.) The COMP pin switches in a parallel compensation network to stabilize the small signal bandwidth with range changes. UDG-94041 |
Аналогичный номер детали - UC3173A |
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Аналогичное описание - UC3173A |
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