View AN982_651792.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

APPLICATION NOTE
USING CERAMIC RESONATORS WITH THE ST7
by Microcontroller Division Applications
INTRODUCTION
The goal of this application note is to show, using results obtained by Murata, that ceramic resonators can be used instead of quartz crystals. Ceramic resonators are cheaper than quartz crystals and as some resonators have built-in capacitors, so they allow you to use less components. The results described here have been obtained for the ST72251 but are also available for ST72101, ST72121, ST72212, ST72213, ST72221, ST72331 and ST72311.
1 CERAMIC RESONATORS FOR ST72251
Murata Electronics is a manufacturer of passive electronic components such as capacitors, filters, oscillators and resonators. They have done several tests with different resonators (CERALOCK) for STMicroelectronics 8-bit microcontrollers at 4 MHz, 8 MHz and 16 MHz. Some resonators have built-in capacitors (see Table 1). The test circuit is shown in Figure 1. Figure 1. Test circuit
VDD (+5V) 28 ST72E251 2 3 27
Rp
CERALOCK V1 C1 C2
Rd
V2
AN982/1098
1/6
1
USING CERAMIC RESONATORS WITH THE ST7
Table 1 shows the recommended conditions at different frequencies. Table 1. Obtained Results
Freq. (MHz) Parts Number CSA4.00MG0401) CST4.00MGW0402) 4 CSAC4.00MGC(M)040 3) CSTCC4.00MG0H64) CSA8.00MTZ1) CST8.00MTW 8
2)
C1 (PF) 100 (100) 100 (47) 30 (30) 30 (47) 10 10
C2 (PF) 100 (100) 100 (47) 30 (30) 30 (47) 10 10
Rp (Ohm) Open Open Open Open Open Open Open Open Open Open
Rd (Ohm) 0 0 0 0 0 0 0 0 0 0
Vdd (V)
3.0 to 5.5
3.0 to 5.5 3.0 to 5.5 4.5 to 5.5
CSACV8.00MTJ3) CSTCC8.00MG0H64) CSA16.00MXZ0401)
16
CSACV16.00MXJ040
3)
Advantages of using ceramic resonators:
s
CST, CSTCC, CSTCV types have built-in loading capacitors (those with values shown in parentheses ()). Rp is always open in the previous table because there is no need for a parallel resistor with a resonator (it is needed only with a crystal).
s
For automotive applications, the Part Number suffix "A" is added except for CSACV and CSTCV types. For SMD-type 8 M Hz resonators for automotive applications, the Part Number is CSTCC8.00MGA0H6. Test conditions:
s
The evaluation conditions are 1.8 to 5.5 V for the supply voltage and -40 to 85 C for the temperature range.
Caution: Above circuit condition is for a design reference only. Recommendable C1, C2 value is dependent on the circuit board used. Request Murata for characterization.
2/6
2
USING CERAMIC RESONATORS WITH THE ST7
Notes: 1) CSA series: ceramic resonators from 1.25 MHz to 60 MHz. Initial frequency tolerance of +/-0.5%. 2) CST series: ceramic resonators from 1.80 MHz to 60 MHz with built-in load capacitors. Initial frequency tolerance of +/- 0.5%. The built-in capacitor values are in parentheses. 3) CSAC series: surface mount ceramic resonators from 1.80MHz to 60MHz. Initial frequency tolerance of +/-0.5%. 4) CSTC series: surface mount ceramic resonators from 1.80MHz to 60MHz with built-in load capacitor. Initial frequency tolerance of +/- 0.5%. The built-in capacitor values are in parentheses.
2 RESULTS AND DIAGRAMS
The diagrams which follow show some of the important features and characteristics of Murata ceramic resonators used with ST72251. Figure 2. Oscillating Frequency vs VDD Characteristics
Osc. Freq. Shift vs Vdd characteristics
0.2 0.15
Oscillating Freq. Shift (%)
0.1 0.05 0 -0.05 -0.1 -0.15 -0.2 0 2 4 6 8
4 MHz 8 MHz 16 MHz
Vdd (V)
We can see in the previous diagram that between 4 and 6 Volts, the biggest frequency shift is 0.025% for the 4MHz curve (1kHz in fact).
3/6
USING CERAMIC RESONATORS WITH THE ST7
Figure 3. Start-up Time vs VDD Characteristics.
Start-up Time vs Vdd characteristics
2
1.5
Start-up Time (ms)
1
maximum operating specifications
4 MHz 8 MHz 16 MHz
0.5
0 2 3 4 5 6 7 8
Vdd (V)
Operating specifications are between 3 and 6 Volts (V DD) for a frequency (fCPU) of between 4 and 8 MHz and 3.5 to 6 Volts (VDD) for an fcpu of 16 MHz. The start-up time is the time the microcontroller takes to reach 90% of the VDD voltage level. In the previous diagram, we can see that the worst case (longest time) is obtained for 3 Volts (about 0.5ms). For a better understanding of what start-up time is, see the following diagram: Power supply
Vdd 0.9Vdd
Start-up time
t
4096 CPU clocks the program starts running
4/6
USING CERAMIC RESONATORS WITH THE ST7
The ST7 microcontroller starts executing the program after an initial delay due to:
s s
the oscillator start-up time a delay of 4096 CPU clock cycles (i.e. 512s at fCPU=8 MHz).
The ceramic resonators used to obtain the previous diagrams were: Table 2. Resonators used in previous tests.
Figure 2 4 MHz 8 MHz 16 MHz CSA4.00MG040 CSA8.00MTZ CSACV16.00MXJ040 Figure 3 CSTCC4.00MG0H6 CSTCC8.00MG0H6 CSA16.00MXZ040
3 CONCLUSION
As shown by the results given in this Application Note, Murata's resonators have been qualified for use as oscillators for ST7 microcontrollers. This means you can use these ceramic resonators in any ST7 application. For more information, you can contact Murata at the following address: Product Engineering Section Toyama Murata Manufacturing Co.,Ltd. 345 Uwano, Toyama-shi, Toyama-ken, Japan 939-8195 Their e-mail address is: www.toyama@murata.co.jp
5/6
USING CERAMIC RESONATORS WITH THE ST7
"THE PRESENT NOTE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH A NOTE AND/OR THE USE MADE BY CUSTOMERS OF THE INFORMATION CONTAINED HEREIN IN CONNEXION WITH THEIR PRODUCTS."
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without the express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c)1998 STMicroelectronics - All Rights Reserved. Purchase of I2C Components by STMicroelectronics conveys a license under the Philips I2C Patent. Rights to use these components in an I2C system is granted provided that the system conforms to the I2C Standard Specification as defined by Philips. STMicroelectronics Group of Companies Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. http://www.st.com
6/6

▲Up To Search▲

Price & Availability of AN982

	To Download AN982 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .