Datasheet

Electrical characteristics ST7LITE20F2 ST7LITE25F2 ST7LITE29F2
144/170 DocID8349 Rev 7
Figure 84. RESET pin protection when LVD is enabled
Figure 85. RESET
pin protection when LVD is disabled
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 can go below the V
IL
max. level specified in Table 82: Asynchronous RESET
Pin. Otherwise the reset will not be 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 for I
INJ(RESET)
in Table 58: Current characteristics.
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.
In case a capacitive power supply is used, it is recommended to connect a 1MΩ pull-down
resistor to the RESET
pin to discharge any residual voltage induced by the capacitive effect
of the power supply (this will add 5µA to the power consumption of the MCU).
Tips when using the LVD:
3. The I
IO
current sunk must always respect the absolute maximum rating and the sum of I
IO
(I/O ports and control pins) must
not exceed I
VSS
.
4. The R
ON
pull-up equivalent resistor is based on a resistive transistor. Specified for voltages on RESET pin between V
ILmax
and V
DD
.
5. To guarantee the reset of the device, a minimum pulse has to be applied to the RESET
pin. All short pulses applied on
RESET
pin with a duration below t
h(RSTL)
in can be ignored.
0.01μF
ST72XXX
PULSE
GENERATOR
Filter
R
ON
V
DD
INTERNAL
RESET
RESET
EXTERNAL
Required
1MΩ
Optional
(note 3)
WATCHDOG
LVD RESET
ILLEGAL
OPCODE
0.01μF
EXTERNAL
RESET
CIRCUIT
USER
Required
ST72XXX
PULSE
GENERATOR
Filter
R
ON
V
DD
INTERNAL
RESET
WATCHDOG
ILLEGAL OPCODE