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TPS2343 Datasheet(PDF) 14 Page - Texas Instruments |
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TPS2343 Datasheet(HTML) 14 Page - Texas Instruments |
14 / 40 page TPS2343 SLUS644B − FEBRUARY 2005 − MAY 2005 14 www.ti.com APPLICATION INFORMATION Turn-On Sequence Main power to the slot turns on when all input supplies are active and power is commanded, by asserting PWRENx. The charge pump combined with the P12VGx capacitor produces a linear voltage ramp on P12VGx, which produces a linear ramping of the 12-V output and the −12-V output. At the same time, a current source on 5VG combined with the 5VG capacitor produces a linear voltage ramp on 5VG and a current source on 3VG combined with the 3VG capacitor produces a linear voltage ramp on 3VG, which produces a linear ramping of the 3.3-V and 5-V main outputs. During this time, if any main slot current exceeds the appropriate over-current threshold for more than the over-current sensitivity time, the slot latches off and remains off until the logic command is turned off and on again. When P12VGx exceeds the 12-V gate good threshold, 5VG exceeds the 5-V good threshold, and 3VG exceeds the 3-V gate good threshold, outputs should be fully ramped and the power MOSFETs should be fully enhanced. +12-V Supply Control The TPS2343 integrates an N-channel power MOSFET for the 12-V supply and a voltage multiplying charge pump to drive the gate of the power MOSFET to 20 V. Inrush current for the 12-V supply is controlled because the slew rate of the 12-V supply is limited. The slew rate for the 12-V supply is set by the capacitor from P12VG to AGND. Slew rate can be estimated as: dV dt + I GATE C P12VGx where CP12VGx is the capacitor from P12VGx to AGND and IGATE is the P12VGx gate charge current. PCI specifications allow for 12-V supply adapter card bulk capacitance of up to 300 µF. This load capacitance causes additional inrush current of: I INRUSH + CLOAD dV dt + 300 mF I GATE C P12VGx Using the recommended value for CP12VGx = 0.022 µF and the typical value for IGATE = 10 µA, average inrush current can be estimated as: I INRUSH + 300 mF 10 mA 0.022 mF + 0.136 A An internal current−sense circuit monitors the 12-V supply. The over-current threshold for the 12-V supply is directly proportional to the resistor from MISET to AGND. Raising the MISET resistor simultaneously raises the current limit threshold for the 12-V, 5-V, 3.3-V and −12-V supplies. For example, to raise the nominal output current from the 12-V supply by 20%, increase the MISET resistor 20%. This resistor can be as high as 12 k Ω if necessary. Osolete Device |
Similar Part No. - TPS2343_15 |
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Similar Description - TPS2343_15 |
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