KL25 CRYSTAL SPECIFICATION

[DolomitiLynx]

Dear All,

I' m designing a microcontroller board based on Kinetis KL25 uC. As a starting point, I have read all the documentations concerning FRDM-KL25 board. My question is about the main Crystal Oscillator: I don't want to use the one used on the FRDM-KL25 board, because I think is too difficult to mount (particularly on the first prototype boards, that will be produced soldering components by hand). I have some difficulties to understand the recommendations done on the datasheet of the micro, so I want to ask you if I am in the correct way.

Here the specifications of the Crystal Quartz I have chosen for my project and the of the Oscillator mounted on FRDM-BOARD:

QUARZO A - "ABM3B-8000MHZ-B2-T" (USED ON FRDM-KL25)

Frequenza: 8 Mhz

Tolleranza:            20 PPM

Stabilita Frequenza:   50 PPM

Capacitanza di Carico: 18 pF

QUARZO B - "EUROQUARTZ - 8.000MHZ 49USMX/30/50/40/18PF/ATF" (ALTERNATIVE)

Frequenza: 8 Mhz

Tolleranza:            30 PPM

Stabilita:             50 PPM

Capacità di Carico     18 pF

Farnell Code:          1640891

Here my three questions:

A) Can I use the CRYSTAL B to clock the uC?

B) Quartz A has four pins, the two crystal connection pins and two gnd pins. Quartz B only two , the crystal connection ones. Is this a problem? What is the function of the two GND pins on QUART A.

C) For the crystal connection to the KL25 uC, I want to use the same circuit proposed on the KL25 schematic, composed by the two 22pF capacitors and the 1 Mega Ohm Resistor. Are this components still OK also with the new Crystal?

D) If the crystal I have chosen is not suitable to work with the KL25 uC, can you propose me suitable Crystal with the same Frequence and a package easy to solder by hand?

Thanks in advance for your courtesly attention.

[Paul_Tian · Accepted solution]

Hi, Gaio

A) Can I use the CRYSTAL B to clock the uC?

Answer: Yes, you can use this crystal.

B) Quartz A has four pins, the two crystal connection pins and two gnd pins. Quartz B only two , the crystal connection ones. Is this a problem? What is the function of the two GND pins on QUART A.

Answer: No, it is not a problem. These two ground pins are used to provide a stable ground for crystal. This is make crystal phase stable.

C) For the crystal connection to the KL25 uC, I want to use the same circuit proposed on the KL25 schematic, composed by the two 22pF capacitors and the 1 Mega Ohm Resistor. Are this components still OK also with the new Crystal?

Answer: The capacitors are needed. The resistor is not a must issue.

D) If the crystal I have chosen is not suitable to work with the KL25 uC, can you propose me suitable Crystal with the same Frequence and a package easy to solder by hand?

Answer:Yes, you can use the crystal you choose.

Hope my reply can help you.

Best Regards

Paul

[kai_liu]

Hello, Zhen Tian,

I have same issue as well. I am designing a small board for KL25Z. I have to replace ABM3B-8000MHZ-B2-T to alternative sources since it is expensive. I want to replace it with another SMT crystal from NDK NX5032GA, and standard HC49 package is too big.

NX5032GA(OA / AV)/Crystal Units/NDK

Nominal frequency (MHz)	8 to 49.99 Please click above Frequency Range(link) to go to NDK's standard frequencies and Ordering Codes page.
Package Size (L×W×H : mm)	5.0×3.2×1.3
Overtone order	Fundamental
Frequency Tolerance (25±3°C)	±30×10-6
Frequency versus temperature characteristics (with reference to 25°C)	±50×10-6
Operating Temperature Range(*1)  /  Storage Temperature Range   (°C)	-40 to +85  /  -40 to +125
Equivalent Series Resistance (Nominal frequency)	Max. 300Ω (8 to 9.5MHz) Max. 150Ω (9.5 to 10MHz) Max. 120Ω (10 to 20MHz) Max. 70Ω (20 to 30MHz) Max. 50Ω (30 to 49.99MHz)
Level of drive	50µW (Max. 500µW)
Load Capacitance	8pF

Should keep the circuit design as it is? (22pF caps plus 1MOhm) One thing is interesting, NDK's trader claim their NX5032GA has different load capacitance for 20pF.

Actually, I want to know how to select/match different cystal, does FSL have AN for that?

[Paul_Tian]

Hi, Liu Kai

1. You cannot use the current circuit if you change crystal.

2. Load capacitor is the most important factor on crystal selection.

3. Sorry, we do not have such an AN or document special on crystal. But I have some experience which can be shared with you.

(1) Accuracy. Please check crystal accuracy first. As normal, I think 50ppm is enough.

(2) Temperature range

Hope my reply can help you.

Best Regards

Paul

[kai_liu]

I found two application notes, although they are not written for Kinetis. But I think FSL will follow its design, since MCG design will be shared in different micro families.

AN2049: Some characteristics and design notes for crystal feedback oscillators (MPC860/68302/68360)

EB675: Limitations of 16MHz crystall oscillators (68HC08/68HC908)

For the 1MOhm R25 on FRDM, it has following discussions. Re: Different freedom board issue

[kai_liu]

Thanks. Paul,

1) Accuray, 30x1o^-6 = 30ppm

2) Temp: 25 degree.

ABM3B-8000MHZ-B2-T has load capacitor as 18pF, and FRDM-KL25Z uses external capacitors for 22pF. According to my Google result, the external capacitor should be about 2 times of load capacitor.

If NX5032GA is 8pF, it should work with 22pF external caps.

If NX5032GA special edition is 20pF, it may have problem.

Isn't it?

[DolomitiLynx]

Thanks for your answers, Mr. Paul.

Best Regards

Giulio