l4969 STMicroelectronics, l4969 Datasheet - Page 23

• Manufacturer Part Number: l4969
• Description: System Voltage Regulator With Fault Tolerant Low Speed Can-transceiver
• Manufacturer: STMicroelectronics

After power-on-reset of VS and V1 or wakeup from Sleep or NRESET being forced low externally, the Startup
Watchdog is active, supervising the proper startup of the V1 supplied uC. Upon missing SPI write operation to
the WDC register after 7 reset cycles (1ms active, 320ms high) the Sleep mode is entered.
Leaving the forced Sleep mode will be automatically performed upon wakeup via CAN, an edge on WAKE or
upon device powerup.
After successful startup, the Window Watchdog supervision is activated, meaning, that the uC has to send an
acknowledge within a predefined, programmable window.
Upon failure, a reset is generated and the Startup Watchdog is reactivated.
If the Timer function is requested, the window watchdog is deactivated until expiry of the wakeup time, or rewrit-
ing of this register. Note, that any write to this register will reset the timer.
2.5.2 Startup
After powerup, the L4969 is expecting the uC to send an acknowledgement within a predefined segmented tim-
ing frame of 7 x 320ms. A missing acknowledgement until after the 2.3s will force the device into sleep mode
until either external or CAN wakeup or POR cause a restart of the sequence above.
2.5.3 Window Watchdog
After successful acknowledgement of the Startup sequence, the Window watchdog is automatically activated
and controlling proper uC activity by supervising an incoming acknowledge to ly within a predefined program-
mable window. Upon every acknowledge the watchdog is restarting the window.
NRESET
V1
NRESET
NRESET
Early (late) Acknowlede supervision
Early (late) Acknowlede supervision
2,5 .. 20ms
Startup Acknowledgement via SPI within 320ms
1ms
Startup Acknowledgement via SPI within 640ms
No Startup Acknowledgement via SPI within 2.3s (Device will enter Sleep mode)
5 .. 40ms
50%
Acknowledge is restarting Window
L4969
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