STMicroelectronics Discovery kit for STM32L151/152 line - with STM32L152RC MCU STM32L152C-DISCO STM32L152C-DISCO Hoja De Datos

DocID022799 Rev 6

time. Refer to the crystal resonator manufacturer for more details on the resonator 
characteristics (frequency, package, accuracy).

          

For C

L1

 and C

L2

, 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 (see 

). C

L1

 and C

L2 

are usually the 

same size. The crystal manufacturer typically specifies a load capacitance which is the 
series combination of C

L1

 and C

L2

. 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 
C

L1

 and C

L2

. Refer to the application note AN2867 “Oscillator design guide for ST 

microcontrollers” available from the ST website www.st.com.

f

OSC_IN

Oscillator frequency

-

1

24

MHz

R

F

Feedback resistor

-

-

200

-

k

 

C

Recommended load 
capacitance versus 
equivalent serial resistance 
of the crystal (R

S

)

(3)

R

S 

= 30



-

20

-

pF

I

HSE

HSE driving current

V

DD

= 3.3 V, 

V

IN 

= V

SS 

with 30 pF 

load

-

-

3

mA

I

DD(HSE)

HSE oscillator power 
consumption

C = 20 pF

f

OSC

 = 16 MHz

-

-

2.5 (startup)

0.7 (stabilized)

mA

C = 10 pF

f

OSC

 = 16 MHz

-

-

2.5 (startup)

0.46 (stabilized)

g

m

Oscillator 
transconductance

Startup

3.5

-

-

mA 

/V

t

SU(HSE)

(4)

Startup time

 V

DD

 is stabilized

-

1

-

ms

1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.

2. Based on characterization results, not tested in production.

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

SU(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.