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TPS61093 Fiches technique(PDF) 11 Page - Texas Instruments |
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TPS61093 Fiches technique(HTML) 11 Page - Texas Instruments |
11 / 25 page 2 2 min_on SW out_skip Vin T f I = 2 (Vout + 0.8V Vin) L ´ ´ ´ - ´ Vout + 0.8 V Vin D = Vout + 0.8 V - SS 0.5 V C5 t = 5 A ´ m TPS61093 www.ti.com SLVS992C – SEPTEMBER 2009 – REVISED JULY 2015 9.2.1.2.3 Start Up The TPS61093 turns on the isolation FET and PWM switch when the EN pin is pulled high. During the soft start period, the R and C network on the SS pin is charged by an internal bias current of 5 μA (typ). The RC network sets the reference voltage ramp up slope. Since the output voltage follows the reference voltage via the FB pin, the output voltage rise time follows the SS pin voltage until the SS pin voltage reaches 0.5 V. The soft start time is given by Equation 2. where • C5 is the capacitor connected to the SS pin (2) When the EN pin is pulled low to switch the IC off, the SS pin voltage is discharged to zero by the resistor R3. The discharge period depends on the RC time constant. Note that if the SS pin voltage is not discharged to zero before the IC is enabled again, the soft start circuit may not slow the output voltage startup and may not reduce the startup inrush current. 9.2.1.2.4 Switch Duty Cycle The maximum switch duty cycle (D) of the TPS61093 is 90% (minimum). The duty cycle of a boost converter under continuous conduction mode (CCM) is given by: (3) The duty cycle must be lower than the specification in the application; otherwise the output voltage cannot be regulated. The TPS61093 has a minimum ON pulse width once the PWM switch is turned on. As the output current drops, the device enters discontinuous conduction mode (DCM). If the output current drops extremely low, causing the ON time to be reduced to the minimum ON time, the TPS61093 enters pulse-skipping mode. In this mode, the device keeps the power switch off for several switching cycles to keep the output voltage in regulation. See Figure 14. The output current when the IC enters skipping mode is calculated with Equation 4. where • Tmin_on = Minimum ON pulse width specification (typically 65-ns); • L = Selected inductor value; • fSW = Converter switching frequency (typically 1.2-MHz) (4) Copyright © 2009–2015, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: TPS61093 |
Numéro de pièce similaire - TPS61093_15 |
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Description similaire - TPS61093_15 |
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