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MIC2026A Datasheet(PDF) 13 Page - Micrel Semiconductor |
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MIC2026A Datasheet(HTML) 13 Page - Micrel Semiconductor |
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13 / 16 page  Micrel, Inc. MIC2026A/2076A July 2009 13 M9999-072309-B (408) 955-1690 Figure 2. MIC2026A Fault Timing Application Information Supply Filtering A 0.1µF to 1µF bypass capacitor positioned close to VIN and GND pins of the device is strongly recommended to control supply transients. Without a bypass capacitor, an output short may cause sufficient ringing on the input (from supply lead inductance) to damage internal control circuitry. Printed Circuit Board Hot-Plug The MIC2026A/2076A are ideal inrush current-limiters for hot plug applications. Due to their integrated charge pumps, the MIC2026A/2076A present a high impedance when off and slowly become a low impedance as their integrated charge pumps turn on. This “soft-start” feature effectively isolates power supplies from highly capacitive loads by reducing inrush current. Figure 3 shows how the MIC2026A may be used in a card hot-plug application. In cases of extremely large capacitive loads (>400µF), the length of the transient due to inrush current may exceed the delay provided by the integrated filter. Since this inrush current exceeds the current-limit delay specification, FLG will be asserted during this time. To prevent the logic controller from responding to FLG being asserted, an external RC filter, as shown in Figure 4, can be used to filter out transient FLG assertion. The value of the RC time constant should be selected to match the length of the transient, less tD(min) of the MIC2026A/2076A. Universal Serial Bus (USB) Power Distribution The MIC2026A/2076A are ideally suited for USB (Universal Serial Bus) power distribution applications. The USB specification defines power distribution for USB host systems such as PCs and USB hubs. Hubs can either be self-powered or bus-powered (that is, powered from the bus). Figure 5 shows a typical USB Host application that may be suited for mobile PC applications employing USB. The requirement for USB host systems is that the port must supply a minimum of 500mA at an output voltage of 5V ±5%. In addition, the output power delivered must be limited to below 25VA. Upon an overcurrent condition, the host must also be notified. To support hot-plug events, the hub must have a minimum of 120µF of bulk capacitance, preferably low ESR electrolytic or tantalum. Please refer to Application Note 17 for more details on designing compliant USB hub and host systems. For bus-powered hubs, USB requires that each downstream port be switched on or off under control by the host. Up to four downstream ports each capable of supplying 100mA at 4.4V minimum are allowed. In addition, to reduce voltage droop on the upstream VBUS, soft-start is necessary. Although the hub can consume up to 500mA from the upstream bus, the hub must consume only 100mA max at start-up, until it enumerates with the host prior to requesting more power. The same requirements apply for bus-powered peripherals that have no downstream ports. Figure 6 shows a bus-powered hub. |
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Similar Description - MIC2026A |
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