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Rev. 1.40
38
March 29, 2019
Rev. 1.40
39
March 29, 2019
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
Crystal/Resonator Oscillator – HXT
Crystal Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
8MHz
0pF
0pF
4MHz
0pF
0pF
1MHz
100pF
100pF
Note:C1 and C2 values are for guidance only.
Crystal Recommended Capacitor Values
External RC Oscillator – ERC
Using the ERC oscillator only requires that a resistor, with a value between 56kΩ and 2.4MΩ,
is connected between OSC1 and VDD, and a capacitor is connected between OSC1 and ground,
providing a low cost oscillator configuration. It is only the external resistor that determines the
oscillation frequency; the external capacitor has no influence over the frequency and is connected
for stability purposes only. Device trimming during the manufacturing process and the inclusion
of internal frequency compensation circuits are used to ensure that the influence of the power
supply voltage, temperature and process variations on the oscillation frequency are minimised. As a
resistance/frequency reference point, it can be noted that with an external 150kΩ resistor connected
and with a 5V voltage power supply and temperature of 25˚C degrees, the oscillator will have a
frequency of 4MHz within a tolerance of 2%. Here only the OSC1 pin is used, which is shared with
I/O pin PC1, leaving pin PC1 free for use as a normal I/O pin.
For oscillator stability and to minimise the effects of noise and crosstalk, it is important to locate the
capacitor and resistor as close to the MCU as possible.
External RC Oscillator – ERC