DP83848M datasheet(33/72 Pages) NSC

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5.4 POWER FEEDBACK CIRCUIT

To ensure correct operation for the DP83848M/J, parallel

caps with values of 10

µF (Tantalum) and 0.1 µF should be

placed close to pin 19 (PFBOUT) of the device.

Pin 16 (PFBIN1) and pin 30 (PFBIN2) must be connected

to pin 19 (PFBOUT), each pin requires a small capacitor

(0.1

µF). See Figure 13 below for proper connections.

5.5 POWER DOWN

The device can be put in a Power Down mode by setting bit

11 (Power Down) in the Basic Mode Control Register,

BMCR (0x00h).

5.6 ENERGY DETECT MODE

When Energy Detect is enabled and there is no activity on

the cable, the DP83848M/J will remain in a low power

mode while monitoring the transmission line. Activity on the

line will cause the DP83848M/J to go through a normal

power up sequence. Regardless of cable activity, the

DP83848M/J will occasionally wake up the transmitter to

put ED pulses on the line, but will otherwise draw as little

power as possible. Energy detect functionality is controlled

via register Energy Detect Control (EDCR), address

0x1Dh.

6.0 Reset Operation

The DP83848M/J includes an internal power-on reset

(POR) function and does not need to be explicitly reset for

normal operation after power up. If required during normal

operation, the device can be reset by a hardware or soft-

ware reset.

6.1 HARDWARE RESET

A hardware reset is accomplished by applying a low pulse

(TTL level), with a duration of at least 1

µs, to the

RESET_N. This will reset the device such that all registers

will be reinitialized to default values and the hardware con-

figuration values will be re-latched into the device (similar

to the power-up/reset operation).

6.2 SOFTWARE RESET

A software reset is accomplished by setting the reset bit

(bit 15) of the Basic Mode Control Register (BMCR). The

period from the point in time when the reset bit is set to the

point in time when software reset has concluded is approx-

imately 1

µs.

The software reset will reset the device such that all regis-

0.1

µF

Pin 19 (PFBOUT)

0.1

µF

0.1

µF

Pin 16 (PFBIN1)

Pin 30 (PFBIN2)

Figure 13. Power Feedback Connection

DP83848M Datasheet(PDF) 33 Page - National Semiconductor (TI)

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