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UCC28C43-Q1 Datasheet(PDF) 15 Page - Texas Instruments |
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UCC28C43-Q1 Datasheet(HTML) 15 Page - Texas Instruments |
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15 / 46 page  < 100 µA VOFF < 3 mA VON VVDD IVDD 15 UCC28C40-Q1, UCC28C41-Q1, UCC28C42-Q1 UCC28C43-Q1, UCC28C44-Q1, UCC28C45-Q1 www.ti.com SLUSA12B – DECEMBER 2009 – REVISED OCTOBER 2017 Product Folder Links: UCC28C40-Q1 UCC28C41-Q1 UCC28C42-Q1 UCC28C43-Q1 UCC28C44-Q1 UCC28C45-Q1 Submit Documentation Feedback Copyright © 2009–2017, Texas Instruments Incorporated 8.3.2 Undervoltage Lockout Three sets of UVLO thresholds are available with turnon and turnoff thresholds of: (14.5 V and 9 V), (8.4 V and 7.6 V), and (7 V and 6.6 V) respectively. The first set is primarily intended for off-line and 48-V distributed power applications, where the wider hysteresis allows for lower frequency operation and longer soft-starting time of the converter. The second group of UVLO options is ideal for high frequency DC-DC converters typically running from a 12-VDC input. The third, and newest, set has been added to address battery powered and portable applications. Table 2 shows the maximum duty cycle and UVLO thresholds by device. Table 2. UVLO Options MAXIMUM DUTY CYCLE UVLO ON UVLO OFF PART NUMBER 100% 14.5 V 9 V UCC28C42-Q1 100% 8.4 V 7.6 V UCC28C43-Q1 100% 7 V 6.6 V UCC28C40-Q1 50% 14.5 V 9 V UCC28C44-Q1 50% 8.4 V 7.6 V UCC28C45-Q1 50% 7 V 6.6 V UCC28C41-Q1 During UVLO thedevicedraws less than 100 µA of supply current. Once crossing the turnon threshold thedevicesupply current increases to a maximum of 3 mA, typically 2.3 mA. This low start-up current allows the power supply designer to optimize the selection of the startup resistor value to provide a more efficient design. In applications where low component cost overrides maximum efficiency, the low run current of 2.3 mA (typical) allows the control device to run directly through the single resistor to (+) rail, rather than requiring a bootstrap winding on the power transformer, along with a rectifier. The start and run resistor for this case must also pass enough current to allow driving the primary switching MOSFET, which may be a few milliamps in small devices. Figure 21. UVLO ON and OFF Profile 8.3.3 ±1% Internal Reference Voltage The BiCMOS internal reference of 2.5 V has an enhanced design, and uses production trim to allow initial accuracy of ±1% at room temperature and ±2% over the full temperature range. This can be used to eliminate an external reference in applications that do not require the extreme accuracy afforded by the additional device. This is useful for nonisolated DC-DC applications, where the control device is referenced to the same common as the output. It is also applicable in off-line designs that regulate on the primary side of the isolation boundary by looking at a primary bias winding, or from a winding on the output inductor of a buck-derived circuit. 8.3.4 Current Sense and Overcurrent Limit An external series resistor (RCS) senses the current and converts this current into a voltage that becomes the input to the CS pin. The CS pin is the noninverting input to the PWM comparator. The CS input is compared to a signal proportional to the error amplifier output voltage; the gain of the current sense amplifier is typically 3 V/V. The peak ISENSE current is determined using Equation 2 |
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