Table 28. Hse Oscillator Characteristics - STMicroelectronics STM32L151RE Manual

Electrical characteristics
Symbol
f Oscillator frequency
OSC_IN
R Feedback resistor
F
Recommended load
capacitance versus
C equivalent serial
resistance of the crystal
(3)
(R )
S
I HSE driving current
HSE
HSE oscillator power
I
DD(HSE)
consumption
Oscillator
g
m
transconductance
(4)
t Startup time
SU(HSE)
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Guaranteed by characterization results.
3. 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 MCU is used in tough humidity conditions.
4. t is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz oscillation is
SU(HSE)
reached. This value is measured for a standard crystal resonator and it can vary significantly with the crystal manufacturer.
For C and C
L1
5 pF to 25 pF range (typ.), designed for high-frequency applications, and selected to match
the requirements of the crystal or resonator (see
same size. The crystal manufacturer typically specifies a load capacitance which is the
series combination of C
can be used as a rough estimate of the combined pin and board capacitance) when sizing
C and C
L1
microcontrollers" available from the ST website www.st.com.
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Table 28. HSE oscillator characteristics

Parameter
V
IN
f
f
V
, it is recommended to use high-quality external ceramic capacitors in the
L2
and C
L1
. Refer to the application note AN2867 "Oscillator design guide for ST
L2
DocID025433 Rev 8
Conditions Min Typ
- 1
- -
= 30 Ω
R -
S
V = 3.3 V,
DD
= V with 30 pF -
SS
load
C = 20 pF
-
= 16 MHz
OSC
C = 10 pF
-
= 16 MHz
OSC
Startup 3.5
is stabilized -
DD
Figure
. PCB and MCU pin capacitance must be included (10 pF
L2
STM32L151xE STM32L152xE
(1)(2)
Max
24
200 -
20 -
- 3
2.5 (startup)
-
0.7 (stabilized)
2.5 (startup)
-
0.46 (stabilized)
- -
1 -
16). C and C are usually the
L1 L2
Unit
MHz
kΩ
pF
mA
mA
mA /V
ms