Table 29. Lse Oscillator Characteristics (F Lse = 32.768 Khz); Figure 17. Hse Oscillator Circuit Diagram - STMicroelectronics STM32L151CB Manual

STM32L151x6/8/B, STM32L152x6/8/B
1. R value depends on the crystal characteristics.
EXT
Low-speed external clock generated from a crystal/ceramic resonator
The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on
characterization results obtained with typical external components specified 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 on the resonator
characteristics (frequency, package, accuracy).
Symbol
f
LSE
R
F
(2)
C
I
LSE
I
DD (LSE)
g
m
(4)
t
SU(LSE)
1. Based on characterization, not tested in production.
2. Refer to the note and caution paragraphs below the table, and to the application note AN2867 "Oscillator
design guide for ST microcontrollers".
3. The oscillator selection can be optimized in terms of supply current using an high quality resonator with
small R
4. t
SU(LSE)
32.768 kHz oscillation is reached. This value is measured for a standard crystal resonator and it can vary
significantly with the crystal manufacturer.

Figure 17. HSE oscillator circuit diagram

Table 29. LSE oscillator characteristics (f
Parameter
Low speed external oscillator
frequency
Feedback resistor
Recommended load capacitance
versus equivalent serial
resistance of the crystal (R
LSE driving current
LSE oscillator current
consumption
Oscillator transconductance
Startup time
value for example MSIV-TIN32.768kHz. Refer to crystal manufacturer for more details.
S
is the startup time measured from the moment it is enabled (by software) to a stabilized
DocID17659 Rev 10
Conditions
-
-
R = 30 kΩ
S
(3)
)
S
V = 3.3 V, V
DD IN
V = 1.8 V
DD
V = 3.0 V
DD
V = 3.6V
DD
-
V is stabilized
DD
Electrical characteristics
Table
(1)
= 32.768 kHz)
LSE
Min Typ
- 32.768
- 1.2
- 8
= V - -
SS
- 450
- 600
- 750
3 -
- 1
29. In
Max Unit
- kHz
- MΩ
- pF
1.1 µA
-
- nA
-
- µA/V
- s
71/129
103