l4969 STMicroelectronics, l4969 Datasheet - Page 14

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

L4969
1.6.3
When entering the sleep mode by writing 1 to DISAR in the VRCR register, the Voltageregulators and their re-
ferences will be deactivated to allow minimum current consumption. By removing the V1 reference, the output-
voltage is no longer supervised and thus NO reset will be generated.
Now two scenarios are possible (see statediagram in chapter 1.2):
1) Wakeup with V1 still above reset threshold: V1 will be reactivated and Normal mode is resumed
2) Wakeup with V1 below reset threshold: V1 will be activated, NRES will go low and remain low until V1 is
above reset threshold and Startup mode is entered.
The scenario 2 is the most critical when used with uC that do not have their own POR circuitry.
In this case V1 will ramp down with an unknown application state.
To guarantee a proper shut off of an uC without an internal POR circuitry the following mechanism can be uti-
lized: The L4969 uses a bidirectional Reset to detect a possible Watchdog failure of the uC. If this failure con-
dition is detected, NRES will be forced low for 1 ms (with activated timer) or until a wakeup condition occurs
(WDEN bit in WDC register reset, thus RC-oscillator will be switched off during sleep).
Two methods can be used to allow a proper sleep transition:
- With Timer (WDEN=1): immediately after setting DISAR the uC has to program its WDC to generate a failure
causing the L4969 to detect a low level on NRES followed by an automatic 1ms pulse extension. If V1 is ramping
down slow, Cext has to be defined in a way, that NRES will stay below the input threshold of the uC until V1 is
in a safe level.
- Without timer (WDEN=0): same procedure as above, but uC has to generate a Reset within 1 ms after WDEN
has been cleared. NRES will then stay low, until a wakeup condition occurs.
.
1.7
A 12-Bit CAN-ID-filter is implemented allowing wakeup via specific CAN-messages thus aiding the implemen-
tation of low power partial communication networks like standby diagnostics without the need to power-up the
whole network.
To guarantee the detection of the programmed Identifiers, the local RC-oscillator can be calibrated to allow the
programmable Bittime logic to extract the incoming stream with a maximum of tolerance over temperature de-
viation.
1.8
In case of single wire communication via CANH the signal to noise ratio is low. Detecting the local ground shift
can be used as an additional indicator on the current signal quality. The information of the integrated ground
shift detector will be refreshed upon every falling edge on TX and can be read from the CAN Transceiver Status
Register (CTSR).
It will be set, if V(CANH) < -1V, reset if V(CANH > -1V) at the falling edge of TX.
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Identifier Filter
Ground Shift Detection
Reset signalling during Sleepmode
DISAR
L4969
REF REG
1ms
RC-Osc
R1
NRES
V1
C
EXT
R2
WDC
C