Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3243E_100_072309

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The SP3243E devices have a patent pending

power in applications such as laptop computers,

palmtop (PDA) computers and other portable

systems.

The SP3243E devices incorporate an AUTO

when the external transmitters are enabled and

the cable is connected. Conversely, the AUTO

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

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.

mode is disabled.

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.