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TPS40057PWPR Fiches technique(PDF) 10 Page - Texas Instruments |
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TPS40057PWPR Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 35 page 1 2 3 4 16 15 14 13 ILIM VIN BOOST HDRV KFF RT BP5 SYNC TPS4005xPWP 5 6 7 8 12 11 10 9 SW BP10 LDRV PGND SGND SS VFB COMP D A 1N914, 1N4150 Type Signal Diode PGND R A 499 kW C A 47 pF R KFF 71.5 kW UDG-08102 ( ) ( ) f A A SW 8 3.48 C R 7.9 - = ´ ´ ( ) ( ) ( ) KFF A IN min R 8 3.48 R 495 k 499 k 0.1 V 3.48 ´ - = = W = W ´ - TPS40054 TPS40055 TPS40057 SLUS593H – DECEMBER 2003 – REVISED JULY 2012 www.ti.com Some applications may require an additional circuit to prevent false restarts at the UVLO voltage level. This applies to applications which have high impedance on the input voltage line or which have excessive ringing on the VIN line. The input voltage impedance can cause the input voltage to sag enough at start up to cause a UVLO shutdown and subsequent restart. Excessive ringing can also affect the voltage seen by the device and cause a UVLO shutdown and restart. A simple external circuit provides a selectable amount of hysteresis to prevent the nuisance UVLO shutdown. Assuming a hysteresis current of 10% IKFF, and the peak detector charges to 8 V and VIN(min) = 10 V, the value of RA is calculated by Equation 3 using a RKFF = 71.5 kΩ. (3) CA is chosen to maintain the peak voltage between switching cycles in order to keep the capacitor charge from drooping 0.1 V (from 8 V to 7.9 V). (4) The value of CA may calculate to less than 10 pF, but some standard value up to 47 pF works adequately. The diode can be a small-signal switching diode or Schottky rated for more then 20 V. Figure 6 illustrates a typical implementation using a small switching diode. The tolerance on the UVLO set point also affects the maximum duty cycle achievable. If the UVLO starts the device at 10% below the nominal start-up voltage, the maximum duty cycle is reduced approximately 10% at the nominal start up voltage. Figure 6. Hysteresis for Programmable UVLO 10 Submit Documentation Feedback Copyright © 2003–2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 |
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