DP83861 datasheet(21/88 Pages) NSC

21 / 88 page

www.national.com

In general, using pull-up and pull-down resistors instead of

tying unused inputs directly to VCC or ground has the fol-

lowing disadvantages:

— Additional cost of components

— Additional board area. (May prevent fitting into fewer lay-

ers of PCB, having components only on the top side, or

fitting into small profile cards.)

— Reliability problems (Due to bad solder joints, etc.)

— Need to test components: Might necessitate additional

vias to be drilled to have test points on the back side, for

in circuit test. This adds to PCB manufacturing time, and

cost. Also testing additional components add to in circuit

test duration, and makes the test program longer to

write.

— Inventory costs for the additional components

3.7 Hardware Reset

RESET pin 164 which is active low should be held low for a

minimum of 140

µs to allow hardware reset. During hard-

ware reset the strap option pins are re-latched, and register

and state machines are reset. For timing details see

Figure 5.7. There is no on-chip internal power-on reset and

the DP83861 requires an external reset signal be applied

to the RESET pin.

3.8 Temperature Considerations

The DP83861 utilizes an enhanced 208 PQFP package

that eliminates the need for heatsinks. The package has a

built in copper heat slug at the top of the package which

provides a very efficient method of removing heat from the

die through convection. Since the heat slug is on the top of

the package the PCB board stays cooler. The enhance

package has a low Theta Junction to Case of 2.13 oC/W

and a Theta Junction to Ambient of 11.7 oC/W.

For reliability purposes the die temperature of the DP83861

should be kept below 120 oC, this translates to a package

case temperature of 112 oC. For more information on how

this calculation is done see Section 8.15 (Frequently Asked

Questions)

3.9 Pin List and Connections

Table 14 provides pin listings and their connections. This

list should be used to make sure all pin connections are

correct.

Table 9. Magnetic Requirements

Parameter

Min.

Typ.

Max.

Units

Conditions

Turns Ratio

1:1

+/- 2%

Insertion Loss

0.0

1.1

0.1 - 1 MHz

0.5

1.0 - 60 MHz

1.0

60 - 100 MHz

1.2

100 - 125 MHz

Return Loss

-18

1.0 - 30 MHz

-14.4

30 - 40 MHz

-13.1

40 - 50 MHz

-12.0

50 - 80 MHz

-10.0

80 - 100 MHz

Differential to Common Mode Rejection

-43.0

1.0 - 30 MHz

-37.0

30 - 60 MHz

-33.0

60 - 100 MHz

Cross Talk

-45.0

1.0 - 30 MHz

-40.0

30 - 60 MHz

-35.0

60 - 100 MHz

Isolation

1500

Rise Time

1.6

1.8

10 - 90%

Primary Inductance

350

µH-

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