AN1709 Datasheet, PDF (17/38 Pages) STMicroelectronics – EMC DESIGN GUIDE FOR ST MICROCONTROLLERS

EMC DESIGN GUIDE FOR ST MICROCONTROLLERS
3 ST MCU DESIGN STRATEGY & EMC SPECIFIC FEATURE
At the initial specification of a new product, EMC dedicated features are implemented after an
identification of EMC constraints imposed by the MCU target applications. You should refer to
the specific product datasheet to know which of these feature described here are embedded.
Figure 10. Overview of specific features embedded in ST Microcontrollers
Low Power Oscillator
Multi Oscillator
Embedded features
for EMC in
ST Microcontrollers
Watchdog
(Firmware Management
refer to AN 1015)
Internal Voltage Regulators
(For MCUs with low power core)
I/O Protection
Controlled Slope
LVD/AVD
Internal PLL
3.1 SUSCEPTIBILITY
3.1.1 Low Voltage Detector (LVD)
The purpose of the LVD is to ensure that the Microcontroller will always work in its safe oper-
ating area (see Figure 12.). In terms of EMS, the presence of the LVD makes the MCU more
robust, ensuring that if any outside disturbance affects the power supply, the application can
recover safely.
When V_DD is below the « Min Working V_DD » the behaviour of the Microcontroller is no longer
guaranteed. There is not enough power to decode/execute the instructions and/or read the
memory. When V_DD is below the LVD level the Microcontroller enters in reset state (internal
reset High) in order to prevent unpredictable behaviour. There are 2 levels with 250mV hys-
teresis in order to avoid oscillating when the micro restarts. When a LVD reset occurs, a bit is
set by HW. This bit can be used to recover an application.
The Low Voltage Detector function generates a static reset when the V_DD supply voltage is
below a V_IT- reference value. This means that it secures the power-up as well as the power-
down keeping the Microcontroller in reset.
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