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SS7529CSTR Datasheet(PDF) 6 Page - Silicon Standard Corp. |
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SS7529CSTR Datasheet(HTML) 6 Page - Silicon Standard Corp. |
6 / 8 page www.SiliconStandard.com 6 of 8 SS7529 Rev.1.01 4/26/2004 FUNCTIONAL DESCRIPTION Operation Overview As graphic-card power design is getting more and more complicated, engineers need a smart solution to reduce not only the design effort, but to further reduce the development time. The SS7529 is targeted at providing application to provide an easy and cost effective solution. The SS7529 control circuit is supplied by 5v and the high- side MOSFET driver is supplied by 12V to eliminate the bootstrap circuit. The SS7529 integrates a synchronous-rectified buck controller and a linear power controller to control the supply of both the high-current requirement of the GPU and the low current requirement of memory. To address fault conditions, UVP (Under-Voltage Protection) is implemented on both outputs and OVP (Over-Voltage Protection) on the linear controller. The high switching frequency (600kHz) helps to reduce component sizes and the output ripple. Initialization There is a smart power-on-reset (POR) circuit to monitor both 5Vcc and 12Vcc to identify if controller has started operation or not. This is to prevent fault conditions from undesirable power sequencing. With this, users can easily implement circuits without worrying about the power sequencing. Soft-Start The POR function initiates the soft-start function after the 5Vcc and 12Vcc reach their threshold voltage. The built-in soft-start function is to prevent inrush current and output voltage overshoot during power on. An internal digital counter controls the soft-start voltage. It clamps the ramping of reference voltage at the input of the error amplifier and increases the pulse width of the output driver slowly. The typical soft-start duration is 3.4mS. Under-Voltage Protection The under-voltage protection (UVP) of the SS7529 is implemented by monitoring the feedback signal at FB and FB2 pins. Whenever one of these two signals drops below 51% of the internal reference, the UVP will be triggered and then both outputs will be quickly shut down. Unless the fault condition is removed, both outputs will keep in hiccup mode operation. Output Voltage Setting Both SS7529 outputs achieve regulation by feedback from the voltage dividers. Therefore, the output voltage can be easily programmed by the resistor values in the following equation. For switching output (figure 7), =0.8V V R R R V OUT Ref 4 1 4 1 = + × SS7529 12VCC 5VCC +5V +12V +3.3V Vout1 UGATE LGATE FB COMP R4 R2 C1 C2 R1 C3 R3 Figure 7. OUTPUT VOLTAGE SELECTION OF THE PWM OUTPUT For linear output (figure 8), R R R V OUT 6 5 6 2 + × = 0.8V Vout2 +3.3Vin SS7529 R5 R6 DRIVER2 FB2 Cout2 Figure 8. OUTPUT VOLTAGE SELECTION OF THE LINEAR OUTPUT Converter Shutdown Forcing the FB2 pin to be higher than a threshold of 1.28V will shutdown both regulators. When the applied voltage is removed, the regulators will return to the re-start cycle and begin the soft-start process. |
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