L4969

14/35

Figure 5.

1.6.3

Reset signalling during Sleepmode

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.

Figure 6. .

1.7

Identifier Filter

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

Ground Shift Detection

1ms sampling

NRES

V1

NRES

DISAR

REF REG

1ms

RC-Osc

R1

R2

WDC

L4969

uC