How to select crystal & load capacitors for the DP83T510E 10Base-T1L Single-Pair Ethernet PHY

If you want to use the DP83T510E’s integrated crystal oscillator, first consider the parameters outlined in the datasheet:

25 MHz nominal frequency
±50ppm overall frequency tolerance (Note: this includes aging etc)
15..20pF recommended load capacitance, maximum of 30pF
Maximum ESR of 150Ω, typical 50Ω

No, you can not use 15pF load capacitors for a 15pF crystal, the number given is the specified load capacitance and you need to calculate the correct values, see below!

These are not very specific selection criteria, so we can basically select a crystal based on price. In this example, we’ll select the YXC X322525MOB4SI since it’s available as a JLCPCB basic component, i.e. no 3$ setup fee, and LCSC/JLCPCB sell it for only 0.0421€/pc @100pcs. Furthermore, it is available in a fairly small 3.2x2.5mm package (small enough to not waste space, large enough so it’s easy to solder if you want to do it yourself).

The X322525MOB4SI has the following parameters:

12pF specified load capacitance
50Ω max ESR
Specified tolerance (see JLCPCB page) of ±20ppm ±10ppm, which I think is initial tolerance and temperature tolerance, so you need to add them up to get the total tolerance of ±30ppm so we’re well within the specified ±50ppm tolerance of the DP83T510E and have some margin left for aging.

Again: 12pF load capacitance does not mean you should use 12pF capacitors, you need to calculate the correct value, see below!

Note that the pin capacitances of the DP83T510E are specified in the 5.5 Electrical Characteristics section of the datasheet:

XI has 1pF pin capacitance
XO has 1pF pin capacitance

Based on this, we can use the Python-based method from our previous post Computing crystal load capacitance using Python & UliEngineering to compute the load capacitors for this configuration.

from UliEngineering.EngineerIO import auto_print
from UliEngineering.Electronics.Crystal import *

auto_print(load_capacitors, cload="12 pF", cpin="1 pF", cstray="2 pF")

This prints 19.0 pF, so we can use 18pF capacitors for the load capacitors, which is the closest standard value.

Now we can select a 18pF capacitor. Other parameters than it having 18pF capacitance are not really relevant, so we could select either of those two from LCSC/JLCPCB, which are also available as basic parts:

0402 package size: 0402CG180J500NT
0603 package size: CL10C180JB8NNNC

0402 is smaller, but harder to place & solder by hand. However, due to its slightly smaller size, it consumed less board space and provides an ever so slightly lower parasitic capacitance and a little bit smaller likelihood of picking up noise from outside or somewhere else in the circuit. Note that this effect is so small it hardly matters in practice.

This is how it would look like in your schematic. Since the ESR already matches quite well, we don’t need to add any series resistance: