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UCC28630DR Datasheet(PDF) 11 Page - Texas Instruments |
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UCC28630DR Datasheet(HTML) 11 Page - Texas Instruments |
11 / 68 page VIN(avg) = VRMS × 2 × ¾2 N tSTART = RHV × CVDD × ln F VIN :avg; VIN :avg; . VDD:start_max;G SD GND VSENSE CS HV VDD DRV UCC28630 1 2 3 4 8 6 5 EMC Filter RHV VAC UCC28630 www.ti.com SLUSBW3A – MARCH 2014 – REVISED MARCH 2014 8.3 Feature Description The application designer requires some key device internal parameters in order to calculate the required power stage components and values for a given design specification . Table 5 summarizes the key parameters. 8.3.1 High-Voltage Current Source Start-Up Operation The controller includes a switched, high-voltage, current source on the HV terminal to allow fast start-up, and eliminates the static power dissipation in a conventional resistive start-up approach. This feature reduces standby power consumption. The HV terminal has three major functions: • Supply the device start-up current • Supply the device bias power from the AC line during latched fault mode • AC sense input for X-capacitor discharge detect The input supply to the HV start-up terminal must be connected to the AC side of the bridge rectifier as shown in Figure 15, in order to support X-capacitor discharge. More details are given in Active X-Capacitor Discharge, below. Connection to the AC side of the bridge also allows faster detection of AC mains removal under latched fault conditions, allowing prompt reset of latched faults for fast restart. Figure 15. HV Terminal Connection to AC Side of Diode Bridge The addition of the 200-k Ω external HV resistance (required for X-capacitor discharge sensing) limits the available charging current for the external bias supply input capacitor. However, for typical values of between 22 µF and 33 µF of input capacitance, start-up bias times of less than 1.5 s are achievable at 90 VAC. Start-up time can be estimated using Equation 1. where • (1) For 90 VAC, if CVDD = 22 µF and worst case VDD(start_max) = 16.5 V, then tSTART is 1.002 s. Figure 16 illustrates the start-up behavior of the controller. The HV current source has built-in short-circuit protection that limits the initial charge current out of the bias voltage terminal until the bias voltage reaches VDD(sc). This limits the power dissipated in the HV current source in the event of a short circuit on the VDD terminal. Thereafter, the HV current source switches to full available current. The controller remains in a low- power, start-up mode until the bias voltage reaches VDD(start), after which the HV current source is turned off and the controller initiates a start-up sequence. Copyright © 2014, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: UCC28630 |
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