DP83959 datasheet(13/38 Pages) NSC

13 / 38 page

4.0

Pin Descriptions (Continued)

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4.8

POWER AND GROUND PINS

The LERIC8 has power and ground (VCC and GND) pins for

each of the major functional blocks of the device. This sec-

tion describes the pairing and decoupling requirements of

the power and ground pins.

4.8.1

Bi-Color LED Power and Ground Pins

These are labeled VCC_LED and GND_LED and are adja-

cent to each other in the following pairs:

Each pair of VCC_LED/GND_LED pins supplies source and

sink current for either 3 or 4 bi-color LED drivers. These

power and ground pins should be decoupled with 0.1

µF ca-

pacitors to reduce noise.

Special Considerations Regarding Icc

Since the drivers source the current required to turn on the

LEDs, the total Icc required by the device will ﬂuctuate de-

pending on network trafﬁc conditions. This should be taken

into consideration when calculating the power requirements

of the system.

4.8.2

Single LED Ground Pins

These are labeled GND_LED and are interspersed amongst

the single LED output driver pins which only have to sink

current to ground. These pins are:

4.8.3

PLL Power and Ground Pins

The LERIC8's receive PLL supply pins (VCC_PLL pin 64 and

GND_PLL pin 65) should be ﬁltered from noise on the nor-

mal +5V VCC supply. The recommended method is with a

µF capacitor in parallel with a 0.01µF capacitor and fed

from VCC via a 22Ω resistor as shown in Figure 1.

4.8.4

AUI and 10BASE-T Port Power and Ground

Pins

The AUI port and eight 10BASE-T ports each have their own

power and ground pair. These should be decoupled with a

0.1

µF capacitor per pair as close to the power/ground pins

as possible.

The AUI and 10BASE-T port power and ground designa-

tions are:

4.8.5

Analog Power and Ground Pins

The transmit wave shaping analog circuitry of the LERIC8

has its own power and ground pair:

This pair should be decoupled with a 10

µF capacitor as

close as possible to the pins. The power and ground feed to

these pins should be kept as quiet as possible.

4.8.6

Crystal Oscillator Power and Ground Pins

The crystal oscillator has its own power and ground pins

(VCC_OSC pin 141 and GND_OSC pin 140). This pair

should be kept relatively noise free and decoupled with a

0.1

µF capacitor as close to the pins as possible.

4.8.7

Digital Power and Ground Pins

The DP83959's digital core logic power supply pins should

be decoupled in pairs with 0.1

µF capacitors as close to the

pins as possible. The digital power and ground pin pairs are

as follows:

VCC/GND_LED 7/8

VCC/GND_LED 15/16

VCC/GND_LED

23/24

GND_LED

148, 153 and 157

Figure 1.

DP83959 PLL Power Supply Decoupling

22Ω

10µ

0.01µF

VDD_PLL

GND_PLL

DP83959

LERIC8

VDD

GND

Port

Power/Ground Names Pin Numbers

AUI

VCC_AUI

GND_AUI

10BASE-T Port 1

VCC_P1

GND_P1

137

136

10BASE-T Port 2

VCC_P2

GND_P2

130

131

10BASE-T Port 3

VCC_P3

GND_P3

125

124

10BASE-T Port 4

VCC_P4

GND_P4

115

116

10BASE-T Port 5

VCC_P5

GND_P5

10BASE-T Port 6

VCC_P6

GND_P6

10BASE-T Port 7

VCC_P7

GND_P7

10BASE-T Port 8

VCC_P8

GND_P8

VCC_ANLG

pin 109

GND_ANLG

pin 110

VCC

GND

-3

106

105

146

147

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