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SI786DRG-T1 Fiches technique(PDF) 8 Page - Vishay Siliconix |
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SI786DRG-T1 Fiches technique(HTML) 8 Page - Vishay Siliconix |
8 / 14 page Si786 Vishay Siliconix www.vishay.com 8 Document Number: 70189 S-40807—Rev. J, 26-Apr-04 ORDERING INFORMATION Part Number Lead (Pb)-Free Part Number Temp Range VOUT Si786CG 33 V Si786CG-T1 Si786CG-T1—E3 3.3 V Si786CRG C-Grade 3 45 V Si786CRG-T1 Si786CRG-T1—E3 C-Grade 0 to 70_C 3.45 V Si786CSG 36 V Si786CSG-T1 Si786CSG-T1—E3 3.6 V Si786LG 33 V Si786LG-T1 Si786LG-T1—E3 3.3 V Si786LRG L-Grade 3 45 V Si786LRG-T1 Si786LRG-T1—E3 L-Grade −10_ to 90_C 3.45 V Si786LSG 36 V Si786LSG-T1 Si786LSG-T1—E3 3.6 V Si786DG 33 V Si786DG-T1 Si786DG-T1—E3 3.3 V Si786DRG D-Grade 3 45 V Si786DRG-T1 Si786DRG-T1—E3 D-Grade −40_ to 85_C 3.45 V Si786DSG 36 V Si786DSG-T1 Si786DSG-T1—E3 3.6 V Demo Board Temp Range Board Type Si786DB 0 to 70_C Surface Mount DESCRIPTION OF OPERATION The Si786 is a dual step-down converter, which takes a 5.5-V to 30-V input and supplies power via two PWM controllers (see Figure 1). These 5-V and 3.3-V supplies run on an optional 300-kHz or 200-kHz internal oscillator, or an external sync signal. Amount of output current is limited by external components, but can deliver greater than 6 A on either supply. As well as these two main Buck controllers, additional loads can be driven from two micropower linear regulators, one 5 V (VL) and the other 3.3 V (REF)—see Figure 2. These supplies are each rated to deliver 5 mA. If the linear regulator circuits fall out of regulation, both Buck controllers are shut down. Two voltage comparators with adjustable output voltages are included in the Si786. They can be used for gate drive in load switching applications, where n-channel MOSFETs are used. Logic level voltages can be generated as well, for instance to serve as mP interfacing (e.g. a Power-good signal). 3.3-V Switching Supply The 3.3-V supply is regulated by a current-mode PWM controller in conjunction with several externals: two n-channel MOSFETs, a rectifier, an inductor and output capacitors (see Figure 1). The gate drive supplied by DH3 needs to be greater than VL , so it is provided by the bootstrap circuit consisting of a 100-nF capacitor and diode connected to BST3 . A low-side switching MOSFET connected to DL3 increases efficiency by reducing the voltage across the rectifier diode. A low value sense resistor in series with the inductor sets the maximum current limit, to disallow current overloads at power-on or in short-circuit situations. The soft-start feature on the Si786 is capacitor programmable; pin SS3 functions as a constant current source to the external capacitor connected to GND. Excess currents at power-on are avoided, and power-supplies can be sequenced with different turn-on delay times by selecting the correct capacitor value. 5-V Switching Supply The 5-V supply is regulated by a current-mode PWM controller which is nearly the same as the 3.3-V output. The dropout voltage across the 5-V supply, as shown in the schematic in Figure 1, is 400 mV (typ) at 2 A. If the voltage at V+ falls, nearing 5 V, the 5-V supply will lower as well, until the VL linear regulator output falls below the 4-V undervoltage lockout threshold. Below this threshold, the 5-V controller is shut off. The frequency of both PWM controllers is set at 300 kHz when the SYNC pin is tied to REF. Connecting SYNC to either GND or VL sets the frequency at 200 kHz. |
Numéro de pièce similaire - SI786DRG-T1 |
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Description similaire - SI786DRG-T1 |
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