Datasheet

STM8S105xx
Electrical characteristics
Symbol Parameter Conditions Min Typ Max Unit
C
(1)
Recommended load
capacitance
(2)
20 pF
I
DD(HSE)
HSE oscillator power
consumption
C = 20 pF,
f
OSC
= 16 MHz
6 (startup)
1.6 (stabilized)
(3)
mA
C = 10 pF,
f
OSC
=16 MHz
6 (startup)
1.2 (stabilized)
(3)
g
m
Oscillator
transconductance
5 mA/V
t
SU(HSE)
(4)
Startup time V
DD
is stabilized 1 ms
Notes:
(1)
C is approximately equivalent to 2 x crystal Cload.
(2)
The oscillator selection can be optimized in terms of supply current using a high quality resonator with small R
m
value. Refer to crystal manufacturer for more details
(3)
Data based on characterization results, not tested in production.
(4)
t
SU(HSE)
is the start-up time measured from the moment it is enabled (by software) to a stabilized 16 MHz
oscillation is reached. This value is measured for a standard crystal resonator and it can vary significantly with the
crystal manufacturer.
Figure 20: HSE oscillator circuit diagram
HSE oscillator critical g
m
equation
g
mcrit
= (2 × Π × f
HSE
)
2
× R
m
(2Co + C)
2
R
m
: Notional resistance (see crystal specification)
L
m
: Notional inductance (see crystal specification)
C
m
: Notional capacitance (see crystal specification)
Co: Shunt capacitance (see crystal specification)
C
L1
= C
L2
= C: Grounded external capacitance
g
m
>> g
mcrit
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