2020 Microchip Technology Inc. DS00003657A-page 1
AN3657
INTRODUCTION
This application note lists the Vectron high-reliability oscillator model numbers that have been characterized for use as
the External Clock of the ATmegaS64M1 series radiation tolerant microcontrollers. These oscillators are the only rec-
ommended external frequency sources for use as the ATmegaS64M1 External Clock. While other suppliers may offer
clocks that meet the specifications, they are not approved reference designs by Microchip, and, as such, the user must
complete his or her own qualification and analysis for fitness of use.
RECOMMENDED OSCILLATORS
The ATmegaS64M1 has three clock source options. This application note specifically addresses the external crystal
oscillators that are recommended for use with the External Clock. Two oscillator frequencies, 4 MHz and 8 MHz, are
recommended in the application note, though any frequency below 8 MHz may be used per Table 30-4 of the
ATmegaS64M1 data sheet. Four different reliability levels of the microcontroller are available. For each of these reliabil-
ity levels, the customer needs to ensure that the corresponding reliability level of the crystal oscillator is correctly spec-
ified to match the application. model numbers are defined in Eight individual oscillator Table 1 (one for each combination
of frequency and reliability level). These oscillators are directly coupled to the XTAL1 pad.
The models chosen are the most cost-effective solutions that meet the requirements of ATmegaS64M1 and the required
reliability level. The 1157 series oscillators recommended are from the Vectron Hi-Rel Oscillator standard OS-68338. All
the devices listed are 3.3V, CMOS, surface mount, 7 mm x 5 mm, ceramic leadless chip carrier oscillators. The subse-
quent paragraphs after Table 1 are provided for reference and compliance purposes.
TABLE 1: RECOMMENDED VECTRON HIGH-RELIABILITY OSCILLATOR MODELS AT TWO
EXTERNAL CLOCK FREQUENCIES
MCU Model Reliability Level External Clock Frequency Oscillator Model Number
ATmegaS64M1-KH-E Prototype (-E) 4 MHz 1157D4M00000BX
ATmegaS64M1-KH-MQ QML-Q equivalent 4 MHz 1157B4M00000BE
ATmegaS64M1-KH-SV QML-V equivalent 4 MHz 1157R4M00000BS
ATmegaS64M1-MA-HP HiREL Plastic 4 MHz 1157C4M00000BB
ATmegaS64M1-KH-E Prototype (-E) 8 MHz 1157D8M00000BX
ATmegaS64M1-KH-MQ QML-Q equivalent 8 MHz 1157B8M00000BE
ATmegaS64M1-KH-SV QML-V equivalent 8 MHz 1157R8M00000BS
ATmegaS64M1-MA-HP HiREL Plastic 8 MHz 1157C8M00000BB
Crystal Oscillators for ATmegaS64M1 Radiation Tolerant
Microcontroller External Clock Input
