Electrical characteristics
ST72344xx, ST72345xx
Figure 115. RESET pin protection when LVD is enabled(1)(2)(3)(4)
1.
The reset network protects the device against parasitic resets.
- The output of the external reset circuit must have an open-drain output to drive the ST7 reset pad.
Otherwise the device can be damaged when the ST7 generates an internal reset (LVD or watchdog).
- Whatever the reset source is (internal or external), the user must ensure that the level on the RESET pin
taken into account internally.
- Because the reset circuit is designed to allow the internal reset to be output in the RESET pin, the user
must ensure that the current sunk on the RESET pin is less than the absolute maximum value specified
2.
When the LVD is enabled, it is recommended not to connect a pull-up resistor or capacitor. A 10nF pull-
down capacitor is required to filter noise on the reset line.
3.
In case a capacitive power supply is used, it is recommended to connect a 1M
Ω pull-down resistor to the
RESET pin to discharge any residual voltage induced by the capacitive effect of the power supply (this will
add 5A to the power consumption of the MCU).
4.
Tips when using the LVD:
1. Check that all recommendations related to the reset circuit have been applied (see notes above)
2. Check that the power supply is properly decoupled (100nF + 10F close to the MCU). Refer to AN1709
and AN2017. If this cannot be done, it is recommended to put a 100nF + 1M
Ω pull-down on the RESET
pin.
3. The capacitors connected on the RESET pin and also the power supply are key to avoid any startup
marginality. In most cases, steps 1 and 2 above are sufficient for a robust solution. Otherwise: replace
10nF pull-down on the RESET pin with a 5F to 20F capacitor.”
5.
Figure 116. RESET pin protection when LVD is disabled(1)
1.
The reset network protects the device against parasitic resets.
- The output of the external reset circuit must have an open-drain output to drive the ST7 reset pad.
Otherwise the device can be damaged when the ST7 generates an internal reset (LVD or watchdog).
- Whatever the reset source is (internal or external), the user must ensure that the level on the RESET pin
taken into account internally.
- Because the reset circuit is designed to allow the internal reset to be output in the RESET pin, the user
must ensure that the current sunk on the RESET pin is less than the absolute maximum value specified
2.
ST72XXX
PULSE
GENERATOR
Filter
RON
VDD
INTERNAL
RESET
EXTERNAL
Required
1 M
Ω
Optional
(note 3)
WATCHDOG
LVD RESET
ILLEGAL OPCODE(5)
0.01 F
EXTERNAL
RESET
CIRCUIT
USER
Required
ST72XXX
PULSE
GENERATOR
Filter
RON
VDD
INTERNAL
RESET
WATCHDOG
ILLEGAL OPCODE(2)
0.01 F