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SP2525A Datasheet(PDF) 8 Page - Exar Corporation |
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SP2525A Datasheet(HTML) 8 Page - Exar Corporation |
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8 / 10 page  S SP P2 25 52 25 5A A S Siin ng glle e C Ch ha an nn ne ell U US SB B P Po ow we err D Diis sttrriib bu uttiio on n S Sw wiittcch h © 2011 Exar Corporation 8/10 Rev. 2.1.0 APPLICATION INFORMATION ERROR FLAG The Error Flag is an open-drained output of an N-channel MOSFET, the FLG output is pulled low to signal the following fault conditions: input undervoltage, output current limit, and thermal shutdown. CURRENT LIMIT The current limit threshold is preset internally. It protects the output MOSFET switches from damage resulting from undesirable short circuit conditions or excess inrush current, which is often encountered during hot plug-in. The low limit of the current limit threshold of the SP2525A allows a minimum current of 0.5A through the MOSFET switches. A current limit condition will signal the Error Flag. THERMAL SHUTDOWN When the temperature of the SP2525A exceeds 135ºC for any reasons, the thermal shutdown function turns off the MOSFET switch and signals the Error Flag. A hysteresis of 10ºC prevents the MOSFETs from turning back on until the chip temperature drops below 125ºC. SUPPLY FILTERING A 0.1μF to 1μF bypass capacitor from IN to GND, located near the device, is strongly recommended to control supply transients. Without a bypass capacitor, an output short may cause ringing on the input (from supply lead inductance) which can damage internal control circuitry. TRANSIENT REQUIREMENTS USB supports dynamic attachment (hot plugin) of peripherals. A current surge is caused by the input capacitance of a downstream device. Ferrite beads are recommended in series with all power and ground connector pins. Ferrite beads reduce EMI and limit the inrush current during hot- attachment by filtering high-frequency signals. SHORT CIRCUIT TRANSIENT Bulk capacitance provides the short-term transient current needed during a hot- attachment event. A 33μF/16V tantalum or a 100μF/ 10V electrolytic capacitor mounted close to the downstream connector at each port should provide sufficient transient drop protection. PRINTED CIRCUIT LAYOUT The Power circuitry of USB printed circuit boards requires a customized layout to maximize thermal dissipation and to minimize voltage drop and EMI. INPUT AND OUTPUT The independent solid state switch connects the IN pin to the OUT pin when enabled by a logic signal at EN. The IN pin is the power supply connection to the internal circuitry and the drain of the output MOSFET. The OUT pin is the source for the MOSFET. Typically, the current in USB application will flow through the switch from IN to OUT towards the load. If VOUT is greater than VIN when a switch is enabled, the current will flow from OUT to the IN pin because the MOSFET channels are bidirectional when switched on. The output source is allowed to be externally forced to a higher voltage than its input without causing unwanted current flow when the output is disabled. TEST CIRCUIT |
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