![](http://datasheet.mmic.net.cn/140000/ST72345C4T6_datasheet_5015341/ST72345C4T6_209.png)
ST72344xx, ST72345xx
Electrical characteristics
13.6.1
Crystal and ceramic resonator oscillators
The ST7 internal clock can be supplied with four different Crystal/Ceramic resonator
oscillators. All the information given in this paragraph is based on characterization results
with specified typical external components. In the application, the resonator and the load
capacitors have to be placed as close as possible to the oscillator pins in order to minimize
output distortion and startup stabilization time. Refer to the crystal/ceramic resonator
manufacturer for more details (frequency, package, accuracy, etc.).
Table 96.
Auto-wakeup from Halt oscillator (AWU) characteristics
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
fAWU
AWU oscillator frequency
50
125
250
kHz
tRCSRT
AWU oscillator startup time
50
s
Table 97.
Crystal/ceramic resonator oscillator characteristics
Symbol
Parameter
Conditions
Min
Max
Unit
fOSC
Oscillator frequency (1)
1.
The oscillator selection can be optimized in terms of supply current using an high quality resonator with
small RS value. Refer to crystal/ceramic resonator manufacturer for more details.
116
MHz
RF
Feedback resistor(2)
2.
Data based on characterisation results, not tested in production. The relatively low value of the RF
resistor, offers a good protection against issues resulting from use in a humid environment, due to the
induced leakage and the bias condition change. However, it is recommended to take this point into
account if the C is used in tough humidity conditions.
20
40
k
Ω
CL1
CL2
Recommended load capacitance versus
equivalent serial resistance of the
crystal or ceramic resonator (RS)
(3)
3.
For CL1 and CL2 it is recommended to use high-quality ceramic capacitors in the 5-pF to 25-pF range (typ.)
designed for high-frequency applications and selected to match the requirements of the crystal or
resonator. CL1 and CL2, are usually the same size. The crystal manufacturer typically specifies a load
capacitance which is the series combination of CL1 and CL2. PCB and MCU pin capacitance must be
included when sizing CL1 and CL2 (10 pF can be used as a rough estimate of the combined pin and board
capacitance).
pF
i2
OSC2 driving current
fOSC= 2 MHz, C0 = 6 pF,
CL1 = CL2 = 68 pF
426
A
fOSC= 4 MHz, C0 = 6 pF,
CL1 = CL2 = 68 pF
425
fOSC= 8 MHz, C0 = 6 pF,
CL1 = CL2 = 40 pF
456
fOSC= 16 MHz, C0 = 7 pF,
CL1 = CL2 = 20 pF
660