STM32F100x4, STM32F100x6, STM32F100x8, STM32F100xB
Table 21. HSE 4-24 MHz oscillator characteristics
Electrical characteristics
(1)(2)
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
fOSC_IN Oscillator frequency
4
8
24
MHz
RF
Feedback resistor
200
k
Recommended load capacitance
versus equivalent serial
CL1
RS = 30
DD = 3.3 V
30
pF
(3)
CL2
resistance of the crystal (RS)(4)
V
i2
HSE driving current
VIN = VSS with 30 pF
load
1
mA
gm
Oscillator transconductance
Startup time
Startup
25
mA/V
ms
tSU(HSE)
VDD is stabilized
2
(5)
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Based on characterization, not tested in production.
3. It is recommended to use high-quality external ceramic capacitors in the 5 pF to 25 pF range (typ.),
designed for high-frequency applications, and selected to match the requirements of the crystal or
resonator. CL1 and CL2, are usually the same size. The crystal manufacturer typically specifies a load
capacitance which is the series combination of CL1 and CL2. PCB and MCU pin capacitance must be
included (10 pF can be used as a rough estimate of the combined pin and board capacitance) when sizing
L1 and CL2
C
.
4. 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.
5. tSU(HSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz
oscillation is reached. This value is measured for a standard crystal resonator and it can vary significantly
with the crystal manufacturer
Figure 19. Typical application with an 8 MHz crystal
Resonator with
integrated capacitors
C
L1
f
OSC_IN
HSE
Bias
controlled
gain
8 MHz
resonator
R
F
STM32F10xxx
OSC_OUT
(1)
R
EXT
C
L2
ai14128b
1. REXT value depends on the crystal characteristics.
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 Table 22. 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).
Doc ID 16455 Rev 2
47/84
STMICROELECTRONICS [ ST ]
