DS36C280TM datasheet(8/9 Pages) NSC

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Unit Load (Continued)

Slew Rate Control

The DS36C280 features an adjustable slew rate control.

This feature allows more control over EMl levels than tradi-

tion fixed edge rate devices. The slew rate control may be

adjusted with or without any external components. The

DS36C280 offers both low power (I

CC 500 µA max) and low

EMI for an RS-485 interface.

The slew rate control is located at pin two of the device and

only controls the driver output edges. The slew rate control

pin (SR) may be left open or shorted to ground, with or

without a resistor. When the SR pin is shorted to ground

without a resistor, the driver output edges will transition

typically 350 ns. When the SR pin is left open, the driver

output edges will transition typically 3 µs. When the SR pin is

shorted to ground with a resistor, the driver output edges will

transition between 350 ns and 3 µs depending on the resis-

tor value. Refer to the slew rate versus resistor value curve

in this datasheet for determining resistor values and ex-

pected typical slew rate value. Please note, when slowing

the edge rates of the device (see Figure 19 ) will decrease

the maximum data rate also.

01205219

FIGURE 18. Input Current vs Input Voltage

Operating Range

Differential Rise/Fall Time

vs Slew Rate Resistor

01205220

FIGURE 19. Slew Rate Resistor

vs Rise/Fall Time

DS36C280TM Datasheet(PDF) 8 Page - National Semiconductor (TI)