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SP3243EBCA-L Datasheet(PDF) 11 Page - Exar Corporation |
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SP3243EBCA-L Datasheet(HTML) 11 Page - Exar Corporation |
11 / 25 page Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com SP3243E_102_060611 11 The SP3243E devices have a patent pending AUTO ON-LINE® circuitry on board that saves power in applications such as laptop computers, palmtop (PDA) computers and other portable systems. The SP3243E devices incorporate an AUTO ON-LINE® circuit that automatically enables itself when the external transmitters are enabled and the cable is connected. Conversely, the AUTO ON-LINE® circuit also disables most of the inter- nal circuitry when the device is not being used and goes into a standby mode where the device typically draws 1µA. This function is externally controlled by the ONLINE pin. When this pin is tied to a logic LOW, theAUTO ON-LINE® function is active. Once active, the device is enabled until there is no activity on the receiver inputs. The receiver input typically sees at least +3V, which are generated from the transmitters at the other end of the cable with a +5V minimum. Minimum recommended charge pump capacitor value Input Voltage Vcc Charge pump capacitor value for SP32XX 3.0V to 3.6V C1 - C4 = 0.1µF 4.5V to 5.5V C1 = 0.047µF, C2 - C4 = 0.33µF 3.0V to 5.5V C1 - C4 = 0.22µF When the external transmitters are disabled or the cable is disconnected, the receiver inputs will be pulled down by their internal 5kΩ resistors to ground. When this occurs over a period of time, the internal transmitters will be disabled and the device goes into a shutdown or standy mode. When ONLINE is HIGH, the AUTO ON-LINE® mode is disabled. The AUTO ON-LINE® circuit has two stages: 1) Inactive Detection 2) Accumulated Delay AUTO ONLINE CIRCUITRY The Exar-patented charge pumps are designed to operate reliably with a range of low cost capacitors. Either polarized or non polarized capacitors may be used. If polarized capacitors are used they should be oriented as shown in the Typical Operating Circuit. The V+ capaci- tor may be connected to either ground or Vcc (polarity reversed.) The charge pump operates with 0.1µF capacitors for 3.3Voperation. Forothersupply voltages,see the table for required capacitor values. Do not use values smaller than those listed. Increasing the capacitor values (e.g., by doubling in value) reduces ripple on the transmitter outputs and may slightly reduce power consumption. C2, C3, and C4 can be increased without changing C1’s value. For best charge pump efficiency locate the charge pump and bypass capacitors as close as possible to the IC. Surface mount capacitors are best for this purpose. Using capacitors with lower equivalent series resistance (ESR) and self-inductance, along with minimizing parasitic PCB trace inductance will optimize charge pump operation. Designersarealsoadvisedtoconsider that capacitor values may shift over time and operating temperature. |
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