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

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1. R

EXT

 value depends on the crystal characteristics.

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 

. 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).

          

OSC_OUT

OSC_IN

f

HSE

 to core

C

L1

C

L2

R

F

STM32

Resonator

Consumption 

control

g

m

R

m

C

m

L

m

C

O

Resonator

ai18235b

f

LSE

Low speed external oscillator 
frequency

-

-

32.768

-

kHz

R

F

Feedback resistor

-

-

1.2

-

M

 

C

(2)

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

S

)

(3)

R

S 

= 30 k



-

8

-

pF

I

LSE

LSE driving current

V

DD 

= 3.3 V, V

IN 

= V

SS

-

-

1.1

µA

I

DD (LSE)

LSE oscillator current 
consumption

V

DD

 = 1.8 V

-

450

-

nA

V

DD

 = 3.0 V

-

600

-

V

DD

 = 3.6V

-

750

-

g

m

Oscillator transconductance

-

3

-

-

µA/V

t

SU(LSE)

(4)

Startup time 

 V

DD

 is stabilized

-

1

-

s

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

S

 value for example MSIV-TIN32.768kHz. Refer to crystal manufacturer for more details.