Datasheet

Electrical parameters STM8L15xx8, STM8L15xR6
90/134 DocID17943 Rev 6
Figure 21. HSE oscillator circuit diagram
HSE oscillator critical g
m
formula
R
m
: Motional resistance (see crystal specification), L
m
: Motional inductance (see crystal specification),
C
m
: Motional capacitance (see crystal specification), Co: Shunt capacitance (see crystal specification),
C
L1
=C
L2
=C: Grounded external capacitance
g
m
>> g
mcrit
LSE crystal/ceramic resonator oscillator
The LSE is available on STM8L151xx and STM8L152xx devices only.
The LSE clock can be supplied with a 32.768 kHz crystal/ceramic resonator oscillator. 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 resonator manufacturer for more details
(frequency, package, accuracy...).
OSC_OUT
OSC_IN
f
HSE
to core
C
L1
#
L2
R
F
STM8
Resonator
Consumption
control
g
m
R
m
C
m
L
m
C
O
Resonator
.47
g
mcrit
2 Π× f
HSE
×()
2
R
m
× 2Co C+()
2
=
Table 32. LSE oscillator characteristics
Symbol Parameter Conditions Min. Typ. Max. Unit
f
LSE
Low speed external oscillator
frequency
32.768 kHz
R
F
Feedback resistor ΔV = 200 mV 1.2 MΩ
C
(1)(2)
Recommended load capacitance 8 pF
I
DD(LSE)
LSE oscillator power consumption
V
DD
= 1.8 V 450
nAV
DD
= 3 V 600
V
DD
= 3.6 V 750
g
m
Oscillator transconductance 3
(3)
µA/V
t
SU(LSE)
(4)
Startup time V
DD
is stabilized 1 s
1. C= C
L1
= C
L2
is approximately equivalent to 2 x crystal C
LOAD
.
2. The oscillator selection can be optimized in terms of supply current using a high quality resonator with a small R
m
value.
Refer to crystal manufacturer for more details.
3. Guaranteed by design. Not tested in production.