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HIP6501AEVAL1 Datasheet(PDF) 10 Page - Intersil Corporation |
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HIP6501AEVAL1 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 14 page 10 FN4749.6 December 30, 2004 Application Guidelines Soft-Start Interval The 5VSB output of a typical ATX supply is capable of 725mA. During power-up in a sleep state, it needs to provide sufficient current to charge up all the output capacitors and simultaneously provide some amount of current to the output loads. Drawing excessive amounts of current from the 5VSB output of the ATX can lead to voltage collapse and induce a pattern of consecutive restarts with unknown effects on the system’s behavior or health. The built-in soft-start circuitry allows tight control of the slew- up speed of the output voltages controlled by the HIP6501A, thus enabling power-ups free of supply drop-off events. Since the outputs are ramped up in a linear fashion, the current dedicated to charging the output capacitors can be calculated with the following formula: , where ISS - soft-start current (typically 10µA) CSS - soft-start capacitor VBG - bandgap voltage (typically 1.26V) Σ(COUTxVOUT) - sum of the products between the capacitance and the voltage of an output. Due to the various system timing events, it is recommended that the soft-start interval not be set to exceed 30ms. Additionally, the recommended soft-start capacitor range spans from 5nF up to 0.22 µF (0.1µF recommended). Shutdown In case of a FAULT condition that might endanger the computer system, or at any other time, the HIP6501A can be shut down by pulling the SS pin below the specified shutdown level (typically 0.8V) with an open drain or open collector device capable of sinking a minimum of 2mA. Pulling the SS pin low effectively shuts down all the pass elements. Upon release of the SS pin, the HIP6501A undergoes a new soft-start cycle and resumes normal operation in accordance to the ATX supply and control pins status. Layout Considerations The typical application employing a HIP6501A is a fairly straight-forward implementation. Similar to any other linear regulators, attention has to be paid to a few potentially sensitive small signal components, such as those connected to high-impedance nodes or those supplying critical by-pass currents. The power components (pass transistors) and the controller IC should be placed first. The controller should be placed in a central position on the motherboard, closer to the memory load if possible. Ensure the VSEN2 connection is properly sized to carry 200mA without significant resistive losses. The pass transistors should be placed on pads capable of heatsinking, matching the device’s power dissipation. Where applicable, multiple via connections to a large internal plane can significantly lower localized device temperature rise. Placement of the decoupling and bulk capacitors should follow a placement reflecting their purpose. As such, the high-frequency decoupling capacitors (CHF) should be placed as close as possible to the load they are decoupling; the ones decoupling the controller (C12V, C5VSB) close to the controller pins, the ones decoupling the load close to the load connector or the load itself (if embedded). The bulk - + FIGURE 11. 2.5/3.3VMEM OUTPUT VOLTAGE SELECTION CIRCUITRY DETAILS FAULT/MSEL 40 µA MEM VOLTAGE SELECT COMP RSEL RSEL VMEM 1k Ω 10k Ω 2.5V 3.3V + - 0.2V I COUT I SS C SS V BG × -------------------------------- Σ C OUT V OUT × () × = FIGURE 12. PRINTED CIRCUIT BOARD ISLANDS VOUT1 Q1 Q2 Q3 Q4 CSS +12VIN CIN VIA CONNECTION TO GROUND PLANE ISLAND ON POWER PLANE LAYER ISLAND ON CIRCUIT/POWER PLANE LAYER CBULK2 HIP6501A C12V VOUT2 VOUT3 SS GND VSEN2 5VDLSB DRV2 3V3DLSB KEY 12V 5VSB +5VSB DLA Q5 CBULK1 CBULK3 C5VSB CHF1 CHF3 5VDL +5VIN CHF2 +3.3VIN 3V3DL HIP6501A |
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