ST AN2751 Application note

AN2751

Application note

L9952GXP power management system IC

Introduction

Today’s industrial community and car makers in particular, recognize reduced fuel consumption and CO2 emission as a competitive and differentiating advantage.

As a consequence, innovative power management solutions are mandatory in automotive embedded systems for solving the dilemma that consists in drastically reducing the overall quiescent current while the number of current sources is continuously increasing. In the meantime, the increasing systems complexity made necessary to integrate advanced fail safe functionalities in order to improve the sustainability and reliability of automotive electronic control units.

The L9952GXP power management system IC has been developed to fulfil both demands. It integrates all functions to build up a complete and configurable supply solution while providing comprehensive fail safe functionality.

The following product and application guide can be considered as a “cookbook” for designing L9952GXP power management based solutions. It is intended to help system, hardware and software developers to enhance, optimize and secure their applications.

This document will first introduce the key features and the main modes for operating a standard system. Advanced options and configurations will then be introduced for addressing more complex requirements. Finally the appendix will cover specific configuration scenarios and diagnostic procedures that need to be carefully handled in order to avoid any undesirable side effects. The L9952GXP software drivers have also been inserted in appendix for a faster and more effective handling of your system.

July 2008

Rev 1

1/91

www.st.com

Contents	AN2751

Contents

1	System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 9
	1.1	Internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	1.2	Key features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	1.3	Standard system configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
2	Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		13
3	Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
	3.1	Power-on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	15
	3.2	NReset generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16

3.2.1 Power-on: cold start detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.2 Failure detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.3 Wake-up source identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.2.4 Microcontroller RAM integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.3 User defined initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4	Watchdog operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		20
	4.1	Initialization - Long Open Window (LOWi) . . . . . . . . . . . . . . . . . . . . . . . .	20
	4.2	Normal operation - window watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
	4.3	Watchdog fail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22

5	Outputs control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .			23
	5.1	Outputs descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		23
		5.1.1	Voltage regulator V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
		5.1.2	Voltage regulator V2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
		5.1.3	High-side drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
		5.1.4	Low-side drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
		5.1.5	Digital outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25

5.2 Outputs control after power-on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.3 Fail Safe Output (FSO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6	Wake-up inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
	6.1 Cyclic contact sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28

2/91

AN2751			Contents
	6.2	Static contact sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . 30
7	Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . 32
	7.1	Initialization diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . 32

7.1.1 Cold start diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7.1.2 Vs power supply: under/over-voltage detection . . . . . . . . . . . . . . . . . . . 34 7.1.3 V1,2 voltage regulators–failing supply detection . . . . . . . . . . . . . . . . . . 35 7.1.4 NReset generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.2 Output drivers diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 7.3 Junction temperature diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7.4 Global error flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7.5 Periodical monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

8	Standby modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		39
	8.1	Preparation before entering standby modes . . . . . . . . . . . . . . . . . . . . . .	39

8.1.1 Wake-up sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8.1.2 Contact sense flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 8.1.3 Read and store input status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 8.1.4 Configure inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 8.1.5 Set ICMP = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 8.1.6 Turn-Off outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 8.1.7 Trigger watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

8.2 Go to standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 8.3 Current monitoring in V1_standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

8.3.1 Wake-up from Vbat_standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

8.4 Wake-up from V1_standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

8.4.1 Wake-up with NReset generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 8.4.2 Wake-up without NReset generation . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

9	Digital outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	62
	9.1 Looping WU inputs in V1_standby mode . . . . . . . . . . . . . . . . . . . . . . . . .	62

9.1.1 Static filter on WU3 rising-edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 9.1.2 Static filter on WU3 falling-edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 9.1.3 Static filter on WU4 falling-edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 9.1.4 Timer 1 filter on WU3 and WU4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 9.1.5 Timer 2 filter on WU3 and WU4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

3/91

Contents	AN2751

9.1.6 Timer 1 filter on WU3 and timer 2 filter on WU4 . . . . . . . . . . . . . . . . . . 68

9.2 Looping HS open-load status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

9.2.1 Timer 1 filter on HS_Out open-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 9.2.2 Timer 2 filter on HS_Out open-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

9.3 Interrupt mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

10	Tips and tricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		76
	10.1	How to clear LIN and INH status bits (SR0, D17, D18) . . . . . . . . . . . . . .	76
	10.2	Switch watchdog from window mode to continuous time-out mode (for
		Flashing of microcontroller) 76
	10.3	Border conditions to be considered when going to standby . . . . . . . . . . .	76

10.3.1 Go_V1_standby after 8x watchdog failure . . . . . . . . . . . . . . . . . . . . . . . 76 10.3.2 Go_V1_standby with watchdog failure and INT mode enabled . . . . . . . 76

10.4 Consequences of using ICMP bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 10.5 Recommended setup on unused pins . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Appendix A L9952GXP software drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Appendix B L9952GXP information summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Reference documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

4/91

AN2751	List of tables

List of tables

Table 1. Vbat_standby: wake-up sources list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Table 2. V1_standby: wake-up sources list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Table 3. Unused pins recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Table 4. L9952GXP information summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Table 5. Reference documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Table 6. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

5/91

List of figures	AN2751

List of figures

Figure 1. Door module system partitioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 2. Internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 3. Standard system configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 4. Correct signal behaviour at power-on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 5. NReset generation and handling overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 6. V1 voltage regulator drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 7. Power-on behaviour: LOWi failed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 8. Power-on procedure without watchdog trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 9. Windows watchdog and trigger timing areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 10. Out_HS current limitation in auto recovery mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 11. LS output behaviour at failing watchdog. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 12. FSO behaviour after LOWi failure, forced Vbat_standby and wake-up event . . . . . . . . . . 27 Figure 13. Cyclic contact sense: contact connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 14. Cyclic contacts sense: wake-up events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 15. Static contact sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Figure 16. Static wake-up by active-high contacts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 17. Static wake-up by active-low contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 18. Power-on diagnosis - detailed flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 19. Voltage thresholds and NReset generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Figure 20. Fast capture of L9952GXP global error flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Figure 21. Preparation for standby flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Figure 22. WU inputs pins configuration for active and standby modes . . . . . . . . . . . . . . . . . . . . . . . 43 Figure 23. Entering V1_standby mode procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Figure 24. Remaining in V1_standby in case of µC activity period <TCW. . . . . . . . . . . . . . . . . . . . . . 46 Figure 25. Wake-up from V1_standby by SPI access after Iv1 >Icmp_rise. . . . . . . . . . . . . . . . . . . . . 47 Figure 26. Wake-up from V1_standby by WU event after Iv1 > Icmp_rise – No NReset issued . . . . . 48 Figure 27. Wake-up from V1_standby after Iv1 > Icmp_rise followed by a watchdog failure . . . . . . . 50 Figure 28. Flowchart: wake-up from Vbat_standby or V1_standby after NReset . . . . . . . . . . . . . . . . 51 Figure 29. Wake-up from Vbat_standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Figure 30. Vbat wake-up outputs behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Figure 31. Wake-up from V1_standby mode / NReset generated . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Figure 32. V1 wake-up: outputs and FSO behaviour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Figure 33. Wake-up from V1_standby mode without NReset generation . . . . . . . . . . . . . . . . . . . . . . 56 Figure 34. Wake-up from V1_standby by LIN (dominant to recessive) with/without pull-up . . . . . . . . 58 Figure 35. Wake-up from V1_standby by LIN (recessive to dominant) with/without pull up . . . . . . . . 59 Figure 36. Wake-up from V1_standby by CAN or LIN – NReset blockage . . . . . . . . . . . . . . . . . . . . . 60 Figure 37. LIN RxD peak after wake-up by CAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Figure 38. V1_standby DO looping - WU3 rising-edge event in static filtering . . . . . . . . . . . . . . . . . . 63 Figure 39. V1_standby DO looping – WU3 falling-edge event in static filtering. . . . . . . . . . . . . . . . . . 64 Figure 40. V1_standby DO looping – WU4 falling-edge event in static filtering. . . . . . . . . . . . . . . . . . 65 Figure 41. V1_standby DO looping – WU3 and WU4 filters in timer 1 mode. . . . . . . . . . . . . . . . . . . . 66 Figure 42. V1_standby DO looping – WU3 and WU4 filters in timer 2 mode. . . . . . . . . . . . . . . . . . . . 67 Figure 43. V1_standby DO looping - WU3 filter in timer 1 and WU4 filter in timer 2 mode . . . . . . . . . 68 Figure 44. V1_standby open-load looping (outs in timer 1 mode, open-load at out 2) . . . . . . . . . . . . 69 Figure 45. V1_standby open-load looping (outs in timer 2 mode, no open-load) . . . . . . . . . . . . . . . . 70 Figure 46. Wake-up from V1_standby mode in interrupt mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Figure 47. V1_standby in INT mode: wake-up by V1 current monitoring. . . . . . . . . . . . . . . . . . . . . . . 72 Figure 48. V1_standby in INT mode: wake-up by V1 current monitoring. . . . . . . . . . . . . . . . . . . . . . . 73 Figure 49. Wake-up form V1_standby in interrupt mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Figure 50. Wake-up form V1_standby in interrupt mode by V1 current monitoring . . . . . . . . . . . . . . . 75

6/91

AN2751	List of abbreviations

List of abbreviations

CAN	Controller Area Network
CR	Control Register
CSN	Chip Select inverted signal of SPI
DI	SPI Data-In
Dig_Out3	Digital output 3 of the L9952GXP
Dig_Out4	Digital output 4 of the L9952GXP
DO	SPI Data-Out
ECU	Electronic Control Unit
FSO	Fail Safe Output
HS	High-Side driver output
ICMP	Current supervision of V1 regulator in V1_standby mode
INH	Inhibit input of L9952GXP designed for connection with CAN controller
LIN 2.1	Local Interconnect Network version 2.1 (SAEJ2602 compatible)
LINPU	Local Interconnect Network Pull-Up
LOWi	Long Open Window
LS	Low-Side Driver Output
MISO	SPI-Master In Slave Out
MOSI	SPI-Master Out Slave In
NReset	Active low Reset output signal - connected to microcontroller.
OC	Over-Current detection
OL	Open-load detection
OP	Operational sense amplifier
OV	Over-voltage failure of VS
POR	Power-On Reset
PWM	Pulse Width Modulation signal
REL	Relay Output-e.g. low side driver
SPI	Serial Peripheral Interface
SR	Status Register
TRIG	Trigger bit to be inverted within a Window Watchdog
TSD	Thermal Shutdown
TW	Temperature Warning
UV	Under-Voltage failure of VS

7/91

List of abbreviations	AN2751
Vbat_standby	Vbat_standby mode
V1_standby	V1_standby mode
WDC	Watchdog Counter
WD	Watchdog
WU	Wakeup input of the L9952GXP
WU1..4	All 4 wakeup inputs of the L9952GXP

8/91

AN2751	System description

1 System description

The L9952GXP is specified for targeting microcontroller based automotive applications such as door modules, body control units and mechatronic subsystems. Thanks to its advanced functionality and wide ranging configuration possibilities, this power management system IC could either address automotive embedded applications than industrial ones.

Figure 1. Door module system partitioning

Contact
Monitoring				M Power Window
		L9952GXP		LED
				LED
	Power Management System Device
LIN				LED
				LED
			M Mirror Adjustment
C AN	CAN		M Mirror Adjustment
	Transceiver
		SPI	M	Mirror Fold
		L9950	M Lock
			M Dead Lock
		Door Actuator		Turn Indicator
		Driver
	STM8A			Safety Light
	µC			Footwell Light
				Exterior Light

Defroster

Due to the tight interdependence between the L9952GXP and its supplied microcontroller, the L9952GXP will also be called “Companion Chip” in this document.

9/91

System description	AN2751

1.1Internal block diagram

Figure 2. highlights the L9952GXP main internal functional blocks.

Figure 2. Internal block diagram

Vbatt

			HS Drivers for
	HSD
			Bulbs or LEDs

Micro	Vreg 1
Peripheral	Vreg 2
Reset	Watch-	Control
Fail-Safe
	dog
Out
PWM			Contact Supply
Inputs
		State
			LSD
Digital			Power Window
Outputs			Relays
Inputs

Contact

Monitor

Current

+

Sense 1

Op

INH

Wake-

Amps

From CAN

up

SPI

+

Sense 2

Current

SPI Bus

LIN Rx

LIN Bus

LIN

LIN Tx

Transceiver

vPower Management

–2 Voltage Regulators

–Contact Monitoring

–Wake up

–HSD 1 Ohm (Contact Supply)

vHigh Side Drivers

–4 x 7 Ohm (LED, Hall)

vLow Side Drivers

–2 x 2 Ohm (Relays)

vOperational Amplifiers

–2 x (e. g. Current Sense)

vLIN 2.1 compliant transceiver

vControl Logic and SPI Interface

PowerSSO-36

The L9952GXP is a power management system IC containing two low drop regulators with advanced contact sense and additional peripheral functions. The integrated standard serial peripheral interface SPI controls all internal operations and provides driver diagnostic functions.

For a complete and detailed description of all internal features please refer to the L9952GXP product specification.

10/91

AN2751	System description

1.2Key features

The L9952GXP integrates the following key features:

●Two very fast transient response voltage regulators - without electrolytic capacitance

●Ultra low quiescent current in standby mode (7 µA)

●LIN 2.1 compliant transceiver

●Configurable contact monitoring - Static, Cyclic, Filtering

●Configurable wakeup procedures through wakeup Contacts, LIN, CAN, SPI

●Window watchdog and fail safe functionality

●Exhaustive system diagnosis through SPI Interface

●Advanced configurable peripherals

–Five High side drivers (1 x 1 Ohms RDSON and 4 x 7 Ohms RDSON)

–Two low side drivers

–Two operational amplifiers with high output voltage

–Two configurable timers with on-chip oscillator

–Two PWM inputs

The key benefits that can be obtained by integrating a L9952GXP in your subsystem are numerous: From the very low system quiescent current, through the cost efficient integration of peripheral functions and the diagnostic features, most of your concerns can be easily and efficiently covered. The following chapters will show you how.

1.3Standard system configuration

This application guide helps to operate the L9952GXP device. Prerequisite for this guide is to use the L9952GXP in the standard configuration of the system hardware. For this standard configuration the detailed behaviour is described under various conditions. If the device is used in other conditions, the behaviour may differ from this description.

Figure 3. gives an example of a system configuration for designing a power window application. This picture is intended to present most of the interconnection possibilities between L9952GXP, microcontroller, external CAN transceiver, LIN Bus, loads, actuators and sensors.

We will first focus on the interconnections between the L9952GXP and the microcontroller. These connections are the most important ones in order to start to operate the device and get used with its functionalities.

11/91

System description	AN2751

Figure 3. Standard system configuration

			VBat
			Vs			VS	V
			Vs				Bat
		V2
				Temp Prewarning
			Voltage	& Shutdown
			Regulator2
		220nF		Overvoltage
CAN	CAN			Shutdown			M
		INH	Wake Up IN			2)
			Vs	Low Side	Rel1
		V1
				output clamp
			Voltage
			Regulator1	Low Side	Rel2	2)
		220nF
				output clamp
						2)
			Voltage			recommended for loads
						placed outside of pcb
			Monitor
		PWM1		+	OP1+
		PWM2		-	OP1-
					OP1out
		NReset
	Microcontroller		Window	+	OP2+		µC (ADC)
			Watchdog	-	OP2-
		CLK
			SPI		OP2out
		DI
			LOGIC
		DO
							e. g. Bulb,
					OUT_HS
		Dig_Out3		High Side			LED, Hall
							Sensor
		Dig_Out4 /
		Interrupt		High Side	Out1
		TxD
		RxD		High Side	Out2
			LIN 2.0 1)				e. g. LED,
		LINPU	SAEJ2602		Out3		Hall Sensor
				High Side
LIN		LIN
			1) .
			LIN2 0 certified		Out4
For detailed information				High Side
see		WU3	Wake Up IN
EMC test report from	ESDLIN 1524 BJ						Cyclic Contact
IBEE Zwickau		WU4		Wake Up IN	WU1		Monitoring
			Wake Up IN
		FSO		Wake Up IN	WU2
	Fail-safe Logic
			GND

The required signals (red coloured) for the standard interconnection between the L9952GXP and microcontroller are:

●V1 (power supply to microcontroller)

●NReset (reset signal to microcontroller)

●SPI (DI, DO, CLK, CSN)

●Dig_Out4/INT (if interrupt mode is required)

●LIN_RxD and LIN_TxD

●INH (from CAN transceiver INH output)

The following signals can also be connected but are not required for the basics operations of the L9952GXP:

●PWM1 and PWM2 (to enter FLASH mode)

●Dig_Out3

12/91

AN2751	Operating modes

2 Operating modes

The L9952GXP power management system IC can be operated in three different major modes:

●Active mode (including Start-up and Flash modes)

●V1_standby mode V1_standby (with or without contact sense)

●Vbat_standby mode Vbat_standby (with or without contact sense)

Depending on the targeted application, a combination of these modes has to be implemented.

The following examples highlight some very different requirements:

●The application needs up to two independent low-drop voltage regulators, High-Side and Low-Side drivers with advanced diagnostic functions and current-sense operational amplifiers.

●The application must continuously supply the microcontroller in order to preserve its memory content.

●The application targets a minimum current consumption and all current sources have to be switched-off when the functional tasks have been completed.

●The application must periodically monitor external sensors and has to perform specific tasks in case of status change or bus activity.

For all these different scenarios, the L9952GXP can provide a suitable and cost-effective solution.

The following figures highlights the different operating modes and the main transitions possibilities between these modes. Please refer to the L9952GXP datasheet document – Figure 3 – operating modes – for further details.

●Active mode covers all the configurations where V1 voltage regulator (microcontroller supply) and L9952GXP outputs (HS and LS drivers) need to be continuously supplied. In active mode, all outputs can be enabled or disabled via SPI control registers access. The V1 regulator can deliver up to 250 mA and V2 regulator up to 100 mA. During Active mode the microcontroller has to trigger periodically a window watchdog.

–Start-up mode is a temporary state of the L9952GXP after power-on. During Start-up all internal registers are initialized to their default values and the Cold Start flag (SR0 bit 19) is set for monitoring the power-on event. This mode is immediately followed by the Active mode.

–Flash mode operates identically to the active mode except the watchdog feature. This mode is needed for microcontroller re-reprogramming purpose: while flashing the microcontroller cannot manage its software routines anymore - This is why the watchdog has to be disabled. For safety reason this mode can only be entered by applying a high voltage signal on PWM2 pin (VPWM2 > 9 V).

●V1_standby mode is a low current mode intended to preserve the RAM content of the microcontroller during low activity phases. Apart from V1 regulator all other outputs and internal loads are switched off. Typically the current consumption without cyclic sensing falls-down to 45 µA. During V1_standby mode, it is also possible to activate the cyclic sensing of external contacts. A standard operating procedure has to be followed

13/91

Operating modes	AN2751

before entering V1_standby mode. All details on this procedure are explained in the “Preparation for Standby” paragraph.

●Vbat_standby mode is intended to minimize the current consumption. All the L9952GXP internal functions are switched-off except the ones for waking-up the device. In Vbat_standby mode the current consumption is reduced to 7 µA typical. During Vbat_standby mode, it is also possible to activate the cyclic sensing of external contacts. Depending on applied settings for external contact supply and contact sense, the current consumption will be in a range of 75 µA typical. A standard operating procedure has to be followed before entering Vbat_standby mode. All details about this procedure are explained in the “Preparation for Standby” paragraph.

14/91

AN2751	Initialization

3 Initialization

3.1Power-on

Figure 4. shows the main signal behaviour after power-on. When Vs voltage is applied, the V1 voltage supplying the microcontroller is immediately turned On thanks to its very fast transient response. Note that no external electrolytic capacitance is needed.

The Fail Safe Output (FSO) is switched to its inactive state - high. However the microcontroller does not know at that time whether a power-on or a wakeup event from any standby mode occurred. Finding the origin of the microcontroller restart is the topic of the initialization diagnosis. Typically the microcontroller power supply - connected to the V1 voltage regulator - is switched off in power off state, Vbat_standby mode and in the case of a hard restart after several successive fails (e.g. 7 successive watchdogs fails).

The microcontroller is restarted by NReset after a wakeup from V1 or after a watchdog fail. During the power-on diagnosis, the root cause of the microcontroller restart should be identified and action taken regarding the previous state. Since after NReset or V1 turn-on the watchdog starts with Long Open Window, all this power on diagnosis has to be done before the Long Open Window expiration (65 ms typical), otherwise the power-on diagnosis will have to be re-started from scratch without any diagnosis on the restart reason or Cold Start event.

Figure 4. Correct signal behaviour at power-on

15/91

Initialization	AN2751

3.2NReset generation

On an automotive system application, many external events - predictable as well as unpredictable ones - may be at the origin of a L9952GXP NReset generation. Depending on supply conditions, thermal conditions, voltage range stability or wakeup events, different diagnosis and actions have to be handled by the application with the highest level of confidence and security.

The following flowchart (Figure 5.) is a reduced overview of the NReset handling in order to treat the possible events in the right priority order. The complete and exhaustive diagnosis procedure is detailed in the Diagnosis chapter. In addition, the dedicated software routine has been inserted in the appendix.

Figure 5. NReset generation and handling overview

Power ON (Cold Start)

Wachdog Failure

OR

Vbatstby Wake-up event

V1stby Wake-up event

V1 < Vrth (for 8 us) event

1/ Check battery connection

2/Check System Integrity:

-Thermal conditions

-Supply ranges

-Micro communication

3/Check Outcoming Power Mode:

-Wake-up from V1 or Vbat standby

-Identify wake-up event

Normal Operation

Fail-Safe Operation

Nreset forced Low Nreset released

Nreset

Low-high transition

									SPI Initialization
	Power-On Detection
									Drivers Inititialization
									SR0 Access
			Y
	Cold Start								Entering Power-On procedure
	N
									Thermal shutdown Detection
	Failure Detection								V1 voltage regulator Failure
									Watchdog Failure
			Y
									System Failure to be
	Failure
									handled at highest level
	N
									Outputs Control
	Wake-up Detection								Diagnosis
									Wake-up source Detection
			Y
									Micro Memory Content
	V1stby mode								was preserved
									Entering Active Mode
	N
	Micro Initialization before
	Entering Active Mode

After L9952GXP power-on - when Vs voltage is turned On - the first action to be performed by the application is the Initialization Procedure.

First the status register SR0 has to be accessed in order to evaluate the cold start bit (SR0 bit 19). The SR0 should be obtained by a CR2 write. After cold start bit evaluation, the SR1 should be read for evaluation of a possible restart after any error. If thermal shutdown neither V1 fail nor WDC Fail Counter is set, there is only wakeup from Vbat_standby mode

16/91

AN2751	Initialization

or wakeup from V1_standby with NReset generation as possible reasons for microcontroller restart.

At this point it is not possible to determine whether the microcontroller was restarted because of power-on or wakeup event from any standby mode. Details regarding wakeup from standby modes as well as explanations on the corresponding parts of flow chart will be deeply described in the Diagnosis chapter. This chapter is aimed to give an initialization overview only.

At the end of power-on diagnosis the watchdog has to be triggered by writing TRIG = 1. As soon as the watchdog is triggered the Long Open Windows expires and the Window Watchdog (WD) is started. It has then to be triggered periodically – typically every 10 ms from the last trigger operation.

3.2.1Power-on: cold start detection

This first step is used for checking system supply status. After power-on, when the supply voltage Vs passes the Power-on-Reset (POR) threshold (3,8 V typical), the “cold start” bit (SR0 bit 19) is latched. Consequently all SPI registers are initialized to their default value. Only a power-on event latches the cold start bit - It is NOT set after waking-up from any standby mode or after any failure occurrence (Thermal Shutdown, V1 Fail, WD Fail…).

Only the first SR0 read access immediately following a power-on returns the cold start flag. This bit is cleared after the first complete SPI frame completion, precisely when the CSN signal is relaxed (rising edge). A complete SPI frame means that 24 SPI_CLK pulses were transmitted while the SPI_CSN signal was low. In the case of an SPI communication Fail, for example, a short on the SPI_CLK signal – the cold start bit is held at 1 until the next SPI frame completion.

3.2.2Failure detection

Vs power supply: under/over-voltage detection

The Vs under/over voltage flags are used to point-out static problems on Vs supply – for example, on the battery (Vbat). By default the sporadic under/over voltage events are not saved, the L9952GXP turns the outputs in high impedance state for load protection and automatically recovers its functionality when the under/over voltage condition has disappeared. For safety reason, two control bits have been implemented to precisely control the outputs behaviour in case of over/under-voltage event.

Please refer to the Diagnosis Chapter for an exhaustive description of this Diagnosis.

V1,2 voltage regulators: failing supply detection

It may be mandatory in safety related applications, to monitor the subsystem microcontroller RAM consistency and if needed to take corrective actions from the upper layer of the

application. The V1,2 voltage regulators flags V1fail and V2fail will point-out disturbances even those coming from short to ground at start-up but also from very short under-voltage

conditions due to electromagnetic noise.

Please refer to the diagnosis chapter for an exhaustive description of this diagnosis.

V1 fail / V2 fail are flags indicating a drop of the voltage regulator output voltage below 2V for at least 2 µs. The flags are also set after power on, if the voltage regulator output doesn’t exceed the 2 V level within 4 ms after turn-on.

17/91

Initialization	AN2751

SHT5V2 is an additional flag for V2 shortcut diagnosis. This flag is set when the output of voltage regulator 2 doesn’t exceed the 2 V level within 4 ms after turn-on.

Watchdog failure

The watchdog has to be served during the open window, typically every 10ms after previous refresh. As soon as the open window expires without a valid trigger, the WD fails. The WD also fails when it is triggered too early means during the closed window. As soon as the WD fails, the NReset signal is pulled down for 2 ms.

3.2.3Wakeup source identification

	After waking-up from V1_standby or Vbat_standby mode, an identification procedure has to
	be performed to find out the wakeup source or event.
	The detailed flowchart of a standard procedure can be found at Figure 28. within Standby
	modes chapter. The generic microcontroller code has been included in the appendix .Those
	frame has to be considered as example guidelines for a safe approach. The priority goes to
	safety or error related information before considering potential wakeup sources. Depending
	on your application needs and priorities this standard frame will have to be adapted.
	After a transition from one operating mode to another, the current state of L9952GXP cannot
	be evaluated. For this reason it is highly recommended after any wakeup event to proceed
	with a full initialization of L9952GXP as shown in Figure 18.: Power-on diagnosis: detailed
	flowchart.
	The wakeup root cause can be identified by reading SR0 bits 13 to 18 The corresponding
	bits have been set in case of a wakeup by LIN, INH or WU inputs 1-4 status change. For WU
	inputs, the initial status was automatically stored before going to standby. A continuous
	comparison between the initial and actual value is operated during contact sensing and the
	corresponding WU input bit is set in case of a status change.
Note:	The previous standby mode from which the L9952GXP was woken-up cannot be identified
	after any wakeup event. In case this information is needed by your application, it has to be
	saved into the microcontroller before going into the specified standby mode.

3.2.4 Microcontroller RAM integrity

This topic can be a very important issue depending on the application. In Normal conditions the RAM content should still be valid, if the power supply voltage didn’t drop under threshold level. Regardless the microcontroller was in halt mode and NReset was processed after wakeup. Typical situations in which the RAM content should have been corrupted are poweron, hard restart after several successive fails and wakeup from Vbat_standby mode.

After wakeup from V1_standby mode, the RAM content should be valid. Due to the fact that the previous standby mode cannot be detected by L9952GXP itself, it will have to be decided – at the application level – whether the RAM content is valid or not. Some microcontrollers integrate power on detection feature that facilitates such arbitration.

18/91

AN2751	Initialization

3.3User defined initialization

Such initializations can be done anytime during run time, but in most applications it is enough do it after start up only.

NReset level is the threshold level of V1 voltage when the NReset pin is pulled-down. This situation can occur only during VS voltage around the under-voltage level and the current of V1 near the limit of over current protection. The V1 regulator has low drop and the output voltage shouldn’t fall under the NReset threshold in standard current range for Vs in operational level. Drop of V1 voltage regulator and voltage level at output in dependence on Vs value and V1 current is shown in Figure 6..

Figure 6. V1 voltage regulator drop

Vs lockout is a control bit which controls the behaviour of the high side output Out 1..4, Out_HS of the low side relay outputs Rel1 and Rel2 and of the LIN Bus in case of Vs over- /under Voltage conditions. When VS lockout bit is set the outputs are automatically disabledmeans turned-off to their default value when an over/under voltage condition is detected. The outputs remain off also when the over/under voltage condition disappears. The over- /under-voltage Status Bits (SR1, D0/D1) have to be cleared in order to turn-on the outputs.

If the Vs lockout bit is not set (default configuration), the outputs are automatically turned On when the over-/under-voltage condition disappears.

19/91

Watchdog operation	AN2751

4 Watchdog operation

4.1Initialization - Long Open Window (LOWi)

After some specific events, the L9952GXP’s window watchdog counter will start to operate with a Long Open Window (LOWi) - typically 65 ms.

The events at the origin of a LOWi are the following:

●“ Cold ” NReset after power-on.

●“ Warm ” NReset under Vs supply.

●“ Wakeup ” from Vbat_standby or from V1_standby modes.

●“ Watchdog Failure ”.

●“ V1 Voltage regulator current increased above the threshold current in V1_standby mode-e.g. Iv1 > Icmp_rise.

The Long Open Window (LOWi) allows the microcontroller to run its own setup through its boot sequence or to recover its normal activity after a “low-power” or “Halt” period before triggering the watchdog via the SPI interface.

During this time slot the watchdog has to be triggered indifferently between the beginning and the end of the Long Open Window.

Figure 7. describes the WD behaviour in case the LOWi expires without a valid trigger. In this case, an active low reset pulse is generated on the NReset output and another LOWi is started. After eight consecutive watchdog failures the V1 is turn-off for 200 ms. After this delay another LOWi is started. If watchdog is still not triggered after seven further consecutive reset procedures, the V1 regulator is completely turned-off and the L9952GXP device goes into Vbat_standby mode until next the wakeup event occurrence (e.g. via LIN, CAN/INH).

When the watchdog is triggered before the LOWi expiration the initialization procedure is over. The microcontroller will then have to trigger the watchdog within the standard periodic open windows (typically every 10 ms).

Figure 7. Power-on behaviour: LOWi failed

Long Open

Window

Reset

V1 turn off

Forced Vbat Standby

for 200ms

Screenshots of the signals behaviour after a power-on with continuous watchdog failures are shown in Figure 8.. As the watchdog was not triggered 15 consecutives times, V1 was switched-off and the device forced to Vbat_standby mode. After the first Long Open Window failure, the Fail Safe Output (FSO) is turned to active (low) state. This output remains active till the next successful watchdog trigger. If the device is switched to force Vbat_standby mode, after wakeup the FSO output is for the first Long Open Window in not active state again until the new watchdog failure occurs (see Figure 8.).

20/91

AN2751	Watchdog operation

Figure 8. Power-on procedure without watchdog trigger

4.2Normal operation - window watchdog

The window watchdog procedure enables periodic control of the microcontroller during normal Operation (Active mode). Any unexpected deviation of the quartz period (even too slow or too fast) may lead to dysfunctions and have dramatic consequences in some security related applications. Thanks to the Watchdog Trigger procedure, both sustainability and correctness of the microcontroller’s frequency are permanently checked.

Figure 9. shows the different watchdog trigger behaviours we can obtain depending on the different corner conditions. A correct watchdog trigger starts the window watchdog with a closed window (from 4.8 ms min. to 7.2 ms max.) followed by an open window (from 8 ms min. to 12 ms max.). The micro has to serve periodically the watchdog by alternating the trigger bit TRIG (CR0-D19) during the open window. A correct watchdog trigger signal will immediately starts the next closed window.

21/91

Watchdog operation	AN2751

Figure 9. Windows watchdog and trigger timing areas

Closed Window				Open Window			Max. Specified
							Timings
Tmax					Tmax
Closed Window			Open Window				Min. Specified
Tmin				Tmin			Timings
Watchdog	Unde-			Safe Trigger	Undefined	Fail
Fail	fined			Area
0	4.8	7.2			12.8	19.2	Time
							[ms]

Note:	The silicon parameters and the corner conditions have a strong impact on the Windows
	Timings. To avoid any potential Watchdog Failures at extreme conditions, it is highly
	recommended to trigger the Watchdog in the middle of the Safe Trigger Area - means
	at 10ms. A WD trigger during the undefined area could either be detected as correct or a
	failing Trigger. WD triggering during a closed windows will causes an “Early write” trigger
	failure. In this case the L9952GXP resets the microcontroller - means NReset Pin is pulled
	low for 2 ms.

Naturally, it is possible to perform at any time a CR0 write access, but the microcontroller has to make sure that the TRIG bit Polarity (CR0-D19) remains unchanged outside the safe trigger area otherwise an “Early write” trigger failure may occur.

4.3Watchdog fail

The watchdog (WD) has to be served during the open window, typically every 10 ms after previous refresh. As soon as the open window expires without a valid trigger, the WD fails. The WD also fails when it is triggered too early means during the closed window. As soon as the WD fails, the NReset signal is pulled down for 2 ms. All outputs are switched off, the FSO output is forced active (low) and the watchdog counter (WDC) (SR1 bits 12 to 15) is incremented e.g. set to 1. After 2 ms, NReset is released to inactive (high) state and the Long Open Window (LOWi) starts.

Note that after waking-up from any standby modes, and during the complete LOWi, the outputs recover the same value as before entering the standby mode. Important is that all outputs are switched off in case of WD failure.

Before the first LOWi expiration, the WD has to be triggered. If the WD is triggered successfully, FSO is switched to inactive (high) and all outputs are configured to their defined values (written in CR0 together with the WD trigger command).

If the WD trigger fails again during LOWi, e.g. LOWi expires without triggering, the NReset is processed again and the WDC is incremented. After 8 successive LOWi without watchdog triggering, the V1 is switched off. After 200 ms V1 is switched on again and 7 additional LOWi are issued. If the WDC reaches 15, L9952GXP is forced to Vbat_standby mode and the WDC is cleared. WDC is also cleared after any valid watchdog trigger. Therefore, if your application wants to monitor the number of successive watchdog failures, the WDC status (SR1 bits 12 to 15) has to be read after any reset event and before watchdog triggering

22/91

AN2751	Outputs control

5 Outputs control

5.1Outputs descriptions

The L9952GXP provides a complete set of outputs for driving different kinds of loads:

●Two 5V low-drop voltage regulators (250 mA and 100 mA continuous mode)

●Five high-side driver outputs for driving LEDs, Bulbs or Hall Sensors

●Two low-side driver outputs for driving relays

●Two digital outputs for driving microcontroller digital inputs

After Vs power-on, CR0, CR1 and CR2 registers are at default value 0x000000. This means that all outputs are switched Off.

Note: Important : Outputs behaviour after a failing watchdog

After a first WD failure, all L9952GXP outputs are turned Off. They cannot be turned on (even during LOWi) until the watchdog is served correctly. As the HS output control bits remain unchanged, the HS outputs will enter the configured state automatically if the watchdog is triggered correctly or after waking-up from forced Vbat_standby mode.

5.1.1Voltage regulator V1

The V1 voltage regulator is the core functionality of the L9952GXP and particular efforts have been spent both for improving the performance and for optimizing the complete system area.

As a result the L9952GXP offers strong differentiating features for serving your application needs:

●Very low quiescent current

●Optimized transient response

●No electrolytic output capacitor need

●Continuous ICMP current monitoring functionality

●Advanced protections against overload, over-temperature, short circuit, reverse biasing

	Exhaustive information on V1 voltage regulator is available in Diagnosis and Standby modes
	chapters. Additionally an information summary in Appendix B covers some specific
	scenarios regarding V1fail and ICMP monitoring topics.
Note:	The V1 voltage regulator is also used for supplying internal logic circuitry and digital outputs
	of the L9952GXP (Dig_out3, Dig_out4 and FSO). As a consequence ICMP is the sum of the
	V1 external current plus the internal logic circuitry and Digital outputs currents.

5.1.2 Voltage regulator V2

Voltage regulator 2 has 4 different operating modes:

● Always Off in all power modes

● Always On in all power modes

● On in run mode only and Off in standby modes

● On in active mode and V1_standby mode; Off in Vbat_standby mode

23/91

Outputs control	AN2751

After voltage regulator V2 has been turned On, the SHT5V2 flag (SR0 bit 12) should be checked to get a status of the regulator output and connected load condition. Details about this flag can be found in diagnosis chapter.

5.1.3High-side drivers

Any of the five High-side outputs can be configured to one of the following modes by setting the corresponding combination of bits in the CR0:

●Off – in this mode the output is switched Off in all operating modes.

●On – in this mode the output is switched On in Active mode and it is switched Off in V1_standby and Vbat_standby modes.

●PWM 1 or PWM 2 – in these modes the output signal is controlled by the signal on the PWM1 or PWM2 input in Active mode. In V1_standby or Vbat_standby mode the output is switched off.

●Timer 1 or Timer 2 – in these modes the output is periodically switched on and off according to the setting of the selected timer. Typically this mode is used to periodically supply the external contacts, synchronized with the cyclic monitoring of the wakeup inputs. This configuration is possible in all operating modes.

Additionally, on HS Out1 to HS Out4 the open load threshold levels can be configured to 2 mA or 8 mA (CR0-D0…D4).

For Out_HS an auto recovery feature is available in active mode (see Figure 10.). This enables driving loads with an initial current higher than the over current limit (e. g. inrush current of cold light bulbs). If the Auto-recovery O_HS_REC bit is set (CR2-D5), Out_HS will automatically be restarted after any over-current shutdown event.

Figure 10. Out_HS current limitation in auto recovery mode

Load

Current Unlimited

Inrush Current

Limited Inrush Current in

programmable Recovery

Mode

Current

Limitation

t

24/91

AN2751	Outputs control

5.1.4Low-side drivers

Two low-side driver outputs Rel1 and Rel2 are available for driving external relays – e.g. for power window control. These outputs can be switched on and off by setting the corresponding bits in the CR0.

The Rel1 and Rel2 output control bits are cleared by default after a first watchdog failure occurrence. Refer to the chapter “Driver Control after power-on” for detailed information.

5.1.5Digital outputs

In both Active and V1_standby modes, the Outputs Dig_out3 and Dig_out4/INT offer the possibility to transmit real time signals from the operating side to the processing side of the application without waiting for a periodical SPI access. Three different configurations are possible:

●Direct looping of WU inputs when status changes.

●Direct looping of High-side open-loads when status changes.

●Interrupt generation when waking-up from V1_standby mode.

A significant advantage of direct looping is the possibility to transmit signals coming from the WU inputs pins - at Vs voltage level to the digital output pins - at TTL voltage level e.g. 5V.

The direct looping of open-load status from High-Side outputs was specifically implemented to connect Hall sensors outputs requiring high real time processing speed. For this purpose the open-load threshold current is configurable on HS Drivers 1 to 4 between 2mA and 8mA (CR2 -bits 0 to 3).

Additionally, the Dig_out4/INT output can be configured (CR1 bit 20) to generate an interrupt signal to the microcontroller (2ms active high pulse) in case of a wakeup from V1_standby mode through WU inputs, LIN, INH, SPI, HS open-load and Iv1 > ICMP_ris. When INT_enable is set to 1 (CR1 bit 20) the looping Option on Dig_out4 is disabled and the NRESET generation is disabled. This specifically addresses applications where the microcontroller must preserve its memory content and have a fast wakeup and fast recovery after an interrupt generation.

All factors influencing the information at the digital outputs are detailed in the digital output chapter.

5.2Outputs control after power-on

All L9952GXP outputs can be switched-on after power-on as soon as the NReset signal has been released untill expiration of the LOWi.

For CR0 write access, the TRIG bit has to be considered with special care. After power-on (means Cold-Start bit is set) the trigger bit polarity has to be set to “1”.

If the outputs are turned On, and watchdog is not triggered, they stay On until the long open window expires. Then the outputs are automatically disabled (turned Off and blocked until a correct watchdog trigger or a wakeup from forced Vbat_standby mode occurs); HS Control Bits in CR0 remain unchanged; LS control bits in CR0 are set to 0) and FSO is turned to active (low) state. After NReset generation, outputs stay off until first successful watchdog trigger. However, every correct watchdog trigger defines the value of all output configurations. So when the watchdog is triggered the outputs are set to configuration that was sent to the L9952GXP during this watchdog trigger procedure (Trigger bit and output

25/91

Outputs control	AN2751

control bits are both located in CR0). On the next screenshot is caught behaviour when REL1 output was turned On after power on. But the watchdog was not triggered and long open window fails 3 times. Than the watchdog was triggered correctly by CR0 with a default value where all outputs are turned off.

Note:	In case of V1_standby mode wakeup event (LIN, INH), the trigger bit was not reset to ‘0’ by
	NReset event. The previous trigger bit polarity should have been stored by the
	microcontroller in order to correctly invert it after waking-up. otherwise the WD is triggered
	with a wrong Trigger bit and the LOWi is closed with a Watchdog failure.

Figure 11. LS output behaviour at failing watchdog

LOW Fail

Rel1 output

turn ON

Watchdog

triggered

Refer also to Figure 12. and observe the REL1 behaviour in a different scenario.

5.3Fail Safe Output (FSO)

The fail safe output is a standard automotive safety functionality implemented for reporting abnormal behaviour of any power management system IC.

In the case of an active FSO signal, external Safety Logic or an additional microcontroller will take-over the control of the security related Drivers so that system sustainability is assured.

The following four events force the FSO output signal to active low state:

●Entering Vbat_standby mode

●Watchdog failure

●V1 under-voltage

●Second thermal shutdown level - TSD2

The next screenshot illustrates a situation where the LOWi fails 15 times after power-on and the device is switched to force Vbat_standby mode. First after power-on, the FSO output remains in its inactive state - high until expiration of the first LOWi. As the watchdog has not been triggered during the LOWi, the device detects a watchdog failure and the FSO signal is

26/91

AN2751	Outputs control

forced to its low active state. The FSO signal remains active until the Watchdog is correctly triggered.

In case the watchdog is correctly triggered before the first LOWi expiration, the FSO stay in inactive state and the L9952GXP outputs are set to the user-defined state, transmitted through the watchdog trigger SPI frame (same write access on CR0 control register).

Note that after wakeup, the LS Output remains Off due to the previous watchdog failure.

The Rel1 output is turned Off at the first watchdog failure and stays off even after a wakeup from forced Vbat_standby mode because the REL1 and REL2 control bits have been cleared after the watchdog failure.

Figure 12. FSO behaviour after LOWi failure, forced Vbat_standby and wakeup event

	Refer also to Figure 11. and observe the FSO behaviour in a different scenario.
Note:	Outputs behaviour during active FSO.
	As soon as FSO enters its active low state, all L9952GXP outputs are turned Off. They
	cannot be turned On (even during LOWi) until the FSO is released – e.g. the watchdog is
	served correctly. As the HS output control bits remain unchanged, the HS outputs will enter
	the configured state automatically if the watchdog is triggered correctly or after waking-up
	from forced Vbat_standby mode. Due to the fact that the trigger bit is within the same
	register than the Outputs configurations bits, you should take care to overwrite the output
	configuration with the correct values each time you will invert the trigger bit (for example by
	applying a software mask).

27/91

Wakeup inputs	AN2751

6 Wakeup inputs

Several settings can be applied on the WU input Pins in order to configure the contact sense to perfectly match with your application requirements. The following two major settings have to be considered:

●The cyclic contact sense supported by both stand-by modes.

●The static contact sense mostly adapted for waking-up from Vbat_standby mode – e.g. for applications where the microcontroller can be completely stopped and where the current consumption has to be drastically minimized.

6.1Cyclic contact sense

Both standby modes support the cyclic sense of the contacts. The main advantage of the cyclic contact supply and sense is a significant reduction in power consumption. For the open active contact (closed in not active state) the power consumption in static mode is approx 10mA for one contact. With the cyclic contact sense, this contact supply current is reduced only to a short time when the contact is checked while the current consumption of the L9952GXP increases by approximately 65uA. Contact sense is done during “On Time” of the timer selected for cyclic sense functionality. During the remaining timer period the contact is not powered and not consuming any power. Of course this feature has an effect for some contact configurations like opening contact, contact which have two stable positions (On/Off) and contacts with a parallel or a parasitic resistive load (e.g. humidity). However, regardless of the configuration, the cyclic monitoring limits the current consumption in case of a stuck contact switch.

To reduce power consumption in the timer Off-time, the proper configuration of each input for current sink or current source has to be done (CR1). The current sink or current source configuration is active only in timer Off Time for cyclic sense to reduce WU input leakage current when the contact is not powered and floating. In time when the contact is checked (timer On Time), the WU input is automatically reconfigured to the setup used in Active mode where an internal pull down of 200 KΩis activated.

For leakage current limitation, the current source configuration is recommended for active low contacts and the current sink configuration is recommended for active high contacts.

28/91