米6体育平台手机版

SNLS250E May 2008 – April 2015 DP83848H , DP83848J , DP83848K , DP83848M , DP83848T

PRODUCTION DATA.

封装选项

机械数据 (封装 | 引脚)

RTA|40
- MPQF134A

散热焊盘机械数据 (封装 | 引脚)

RTA|40
- QFND447B

订购信息

7 Application, Implementation, and Layout

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

7.1 Application Information

The device is a physical layer Ethernet transceiver. Typical operating voltage is 3.3 V with power consumption less than 270 mW. When using the device for Ethernet application, it is necessary to meet certain requirements for normal operation of device. Following typical application and design requirements can be used for selecting appropriate component values for DP83848.

7.2 Typical Application

DP83848H DP83848J DP83848K DP83848M DP83848T typ_app_snls250.png

Figure 7-1 Typical Application Schematic

7.2.1 Design Requirements

The design requirements for DP83848 are:

V_IN = 3.3 V
V_OUT = V_CC – 0.5 V
Clock Input = 25 MHz for MII and 50 MHz for RMII

7.2.1.1 TPI Network Circuit

Figure 7-2 shows the recommended circuit for a 10/100 Mb/s twisted pair interface. Below is a partial list of recommended transformers. It is important that the user realize that variations with PCB and component characteristics require that the application be tested to ensure that the circuit meets the requirements of the intended application.

Pulse H1102
Pulse H2019
Pulse J0011D21
Pulse J0011D21B

DP83848H DP83848J DP83848K DP83848M DP83848T 10_100_Mv_s_twisted_pair_snls250.gif

Figure 7-2 10/100 Mb/s Twisted Pair Interface

7.2.1.2 Clock IN (X1) Recommendations

The DP83848x supports an external CMOS level oscillator source or a crystal resonator device.

7.2.1.2.1 Oscillator

If an external clock source is used, X1 should be tied to the clock source and X2 should be left floating.

The CMOS oscillator specifications for MII Mode are listed in Table 7-1. For RMII Mode, the CMOS oscillator specifications are listed in Table 7-2. For RMII mode, it is not recommended that the system clock out, Pin 21 of DP83848H, DP83848M, or DP83848T devices, be used as the reference clock to the MAC without first verifying the interface timing. See AN-1405 for more details.

7.2.1.2.2 Crystal

A 25-MHz, parallel, 20-pF load crystal resonator should be used if a crystal source is desired. Figure 7-3 shows a typical connection for a crystal resonator circuit. The load capacitor values will vary with the crystal vendors; check with the vendor for the recommended loads.

The oscillator circuit is designed to drive a parallel resonance AT cut crystal with a minimum drive level of 100 µW and a maximum of 500 µW. If a crystal is specified for a lower drive level, a current limiting resistor should be placed in series between X2 and the crystal.

As a starting point for evaluating an oscillator circuit, if the requirements for the crystal are not known, CL1 and CL2 should be set at 33 pF, and R1 should be set at 0 Ω.

Specification for 25-MHz crystal are listed in Table 7-3.

DP83848H DP83848J DP83848K DP83848M DP83848T crystal_oscillator_circuit_snls250.gif

Figure 7-3 Crystal Oscillator Circuit

Table 7-1 25-MHz Oscillator Specification

PARAMETER	CONDITION	MIN	TYP	MAX	UNIT
Frequency			25		MHz
Frequency Tolerance	Operational Temperature			50	ppm
Frequency Stability	1 year aging			50	ppm
Rise / Fall Time	20%–80%			6	nsec
Jitter	Short term			800⁽¹⁾	psec
Jitter	Long term			800⁽¹⁾	psec
Symmetry	Duty Cycle	40%		60%

(1) This limit is provided as a guideline for component selection and not guaranteed by production testing. Refer to SNLA076, PHYTER 100 Base-TX Reference Clock Jitter Tolerance, for details on jitter performance.

Table 7-2 50-MHz Oscillator Specification

PARAMETER	CONDITION	MIN	TYP	MAX	UNIT
Frequency			50		MHz
Frequency Tolerance	Operational Temperature			50	ppm
Frequency Stability	1 year aging			50	ppm
Rise / Fall Time	20%–80%			6	nsec
Jitter	Short term			800⁽¹⁾	psec
Jitter	Long term			800⁽¹⁾	psec
Symmetry	Duty Cycle	40%		60%

Table 7-3 25-MHz Crystal Specification

PARAMETER	CONDITION	MIN	TYP	MAX	UNIT
Frequency			25		MHz
Frequency Tolerance	Operational Temperature			50	ppm
Frequency Stability	1 year aging			50	ppm
Load Capacitance		25		40	pF

7.2.1.3 Power Feedback Circuit

To ensure correct operation for the DP83848x, 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 7-4 for proper connections.

DP83848H DP83848J DP83848K DP83848M DP83848T power_feedback_connection_snls250.gif

Figure 7-4 Power Feedback Connection

7.2.1.4 Magnetics

The magnetics have a large impact on the PHY performance as well. While several components are listed below, others may be compatible following the requirements listed in Table 6-4. It is recommended that the magnetics include both an isolation transformer and an integrated common mode choke to reduce EMI. When doing the layout, do not run signals under the magnetics. This could cause unwanted noise crosstalk. Likewise void the planes under discrete magnetics, this will help prevent common mode noise coupling. To save board space and reduce component count, an RJ-45 with integrated magnetics may be used.

Table 7-4 Magnetics Requirements

PARAMETER	TYP	UNITS	CONDITION
Turn Ratio	1:1	—	±2%
Insertion Loss	-1	dB	1-100 MHz
Return Loss	-16	dB	1-30 MHz
	-12	dB	30-60 MHz
	10	dB	60-80 MHz
Differential to Common Rejection Ratio	-30	dB	1-50MHz
Differential to Common Rejection Ratio	-20	dB	50-150 MHz
Crosstalk	-35	dB	30 MHz
Crosstalk	-30	dB	60 MHz
Isolation	1,500	dB	HPOT

7.2.2 Detailed Design Procedure

7.2.2.1 MAC Interface (MII/RMII)

The Media Independent Interface (MII) connects the PHYTER component to the Media Access Controller (MAC). The MAC may in fact be a discrete device, integrated into a microprocessor, CPU or FPGA. On the MII signals, the IEEE specification states the bus should be 68-Ω impedance. For space critical designs, the PHYTER family of products also support Reduced MII (RMII). For additional information on this mode of operation, refer to the AN-1405 DP83848 Single 10/100 Mb/s Ethernet Transceiver Reduced Media Independent Interface (RMII) Mode Application Report (SNLA076).

7.2.2.1.1 Termination Requirement

To reduce digital signal energy, 50-Ω series termination resistors are recommended for all MII output signals (including RXCLK, TXCLK, and RX Data signals.)

7.2.2.1.2 Recommended Maximum Trace Length

Although RMII and MII are synchronous bus architectures, there are a number of factors limiting signal trace lengths. With a longer trace, the signal becomes more attenuated at the destination and thus more susceptible to noise interference. Longer traces also act as antennas, and if run on the surface layer, can increase EMI radiation. If a long trace is running near and adjacent to a noisy signal, the unwanted signals could be coupled in as cross talk. It is recommended to keep the signal trace lengths as short as possible. Ideally, keep the traces under 6 inches. Trace length matching, to within 2 inches on the MII or RMII bus is also recommended. Significant differences in the trace lengths can cause data timing issues. As with any high speed data signal, good design practices dictate that impedance should be maintained and stubs should be avoided throughout the entire data path.

7.2.2.2 Calculating Impedance

The following equations can be used to calculate the differential impedance of the board. For microstrip traces, a solid ground plane is needed under the signal traces. The ground plane helps keep the EMI localized and the trace impedance continuous. Because stripline traces are typically sandwiched between the ground/supply planes, they have the advantage of lower EMI radiation and less noise coupling. The trade off of using strip line is lower propagation speed.

7.2.2.2.1 Microstrip Impedance – Single-Ended

Equation 1. DP83848H DP83848J DP83848K DP83848M DP83848T eq_zo1_snls266.gif

DP83848H DP83848J DP83848K DP83848M DP83848T MSSingle.png

Figure 7-5 Microstrip Impedance – Single-Ended

7.2.2.2.2 Stripline Impedance – Single-Ended

Equation 2. DP83848H DP83848J DP83848K DP83848M DP83848T eq_zo2_snls266.gif

DP83848H DP83848J DP83848K DP83848M DP83848T STSingle.png

Figure 7-6 Stripline Impedance – Single-Ended

7.2.2.2.3 Microstrip Impedance – Differential

Equation 3. DP83848H DP83848J DP83848K DP83848M DP83848T eq_zdiff1_snls266.gif

DP83848H DP83848J DP83848K DP83848M DP83848T MSDiff.png

Figure 7-7 Microstrip Impedance – Differential

7.2.2.2.4 Stripline Impedance – Differential

Equation 4. DP83848H DP83848J DP83848K DP83848M DP83848T eq_zdiff2_snls266.gif

DP83848H DP83848J DP83848K DP83848M DP83848T STDiff.png

Figure 7-8 Stripline Impedance – Differential

7.2.3 Application Curves

DP83848H DP83848J DP83848K DP83848M DP83848T wvfrm_01_samp_100_mbs_snls250.png

Figure 7-9 Sample 100 Mb/s Waveform (MLT-3)

DP83848H DP83848J DP83848K DP83848M DP83848T wvfrm_02_samp_10_mbs_snls250.png

Figure 7-10 Sample 10 Mb/s Waveform

7.3 Layout

7.3.1 Layout Guidelines

Place the 49.9-Ω,1% resistors, and 0.1-μF decoupling capacitor near the PHYTER TD+/- and RD+/- pins and via directly to the V_DD plane.

Stubs should be avoided on all signal traces, especially the differential signal pairs. See Figure 7-11. Within the pairs (for example, TD+ and TD-) the trace lengths should be run parallel to each other and matched in length. Matched lengths minimize delay differences, avoiding an increase in common mode noise and increased EMI. See Figure 7-11.

DP83848H DP83848J DP83848K DP83848M DP83848T differ_signal_pair_stubs_snls250.gif

Figure 7-11 Differential Signal Pair - Stubs

Ideally, there should be no crossover or via on the signal paths. Vias present impedance discontinuities and should be minimized. Route an entire trace pair on a single layer if possible. PCB trace lengths should be kept as short as possible.

Signal traces should not be run such that they cross a plane split. See Figure 7-12. A signal crossing a plane split may cause unpredictable return path currents and would likely impact signal quality as well, potentially creating EMI problems.

DP83848H DP83848J DP83848K DP83848M DP83848T differ_signal_pair_signal_snls250.png

Figure 7-12 Differential Signal Pair-Plane Crossing

MDI signal traces should have 50 Ω to ground or 100-Ω differential controlled impedance. Many tools are available online to calculate this.

7.3.1.1 PCB Layer Stacking

To meet signal integrity and performance requirements, at minimum a 4-layer PCB is recommended for implementing PHYTER components in end user systems. The following layer stack-ups are recommended for four, six, and eight-layer boards, although other options are possible.

DP83848H DP83848J DP83848K DP83848M DP83848T pcb_strplne_lay_stckng_snls250.gif

Figure 7-13 PCB Stripline Layer Stacking

Within a PCB it may be desirable to run traces using different methods, microstrip vs. stripline, depending on the location of the signal on the PCB. For example, it may be desirable to change layer stacking where an isolated chassis ground plane is used. Figure 7-14 illustrates alternative PCB stacking options.

DP83848H DP83848J DP83848K DP83848M DP83848T alt_pcb_strplne_lay_stckng_snls250.png

Figure 7-14 Alternative PCB Stripline Layer Stacking

7.3.2 Layout Example

DP83848H DP83848J DP83848K DP83848M DP83848T layout_example_snls250.gif

Figure 7-15 Layout Example

7.4 Power Supply Recommendations

The device V_DD supply pins should be bypassed with low-impedance 0.1-μF surface mount capacitors. To reduce EMI, the capacitors should be places as close as possible to the component V_DD supply pins, preferably between the supply pins and the vias connecting to the power plane. In some systems it may be desirable to add 0-Ω resistors in series with supply pins, as the resistor pads provide flexibility if adding EMI beads becomes necessary to meet system level certification testing requirements. (See Figure 7-14) It is recommended the PCB have at least one solid ground plane and one solid V_DD plane to provide a low impedance power source to the component. This also provides a low impedance return path for non-differential digital MII and clock signals. A 10.0-μF capacitor should also be placed near the PHY component for local bulk bypassing between the V_DD and ground planes.

DP83848H DP83848J DP83848K DP83848M DP83848T vdd_bypass_layout_snls250.gif

Figure 7-16 V_DD Bypass Layout