L9678TR - Automotive SBC for Airbag Systems | STMicroelectronics
MPN: L9678TR ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $5.45 | $5.45 |
| 10 | $4.9 | $49.00 |
| 100 | $4.35 | $435.00 |
| 500 | $3.92 | $1,960.00 |
| 1,000 | $3.51 | $3,510.00 |
L9678TR Overview
A System Basis Chip (SBC) is a category of mixed-signal power management IC that consolidates multiple discrete functions - typically a buck/linear regulator, watchdog, communication transceiver, and sensor diagnostics - into a single silicon die. The SBC sits hierarchically below the main microcontroller in an automotive ECU, providing both power conversion and safety monitoring. L9678TR is purpose-built for occupant-safety modules such as airbag ECUs and seatbelt pretensioners, where ASIL-B functional safety classification and continuous diagnostic coverage are mandatory.
Key features include a high-efficiency 5V/3.3V LDO with integrated power-good signal, a programmable windowed watchdog with selectable timeout, dual squib drivers with on-chip current limiting, and SPI communication at up to 5 MHz for configuration and fault readback. The device also integrates a sensor-supply output, arming logic, and a high-side driver for warning lamp control. A typical application circuit uses the L9678TR as the single supply and safety island for an airbag control unit (ACU) hosting an SPC56 or SPC58 automotive MCU.
From an architectural perspective, the L9678TR uses a BCD (Bipolar-CMOS-DMOS) process that allows the 35V-tolerant power paths and the squib-driver high-current outputs to coexist with the low-voltage CMOS control logic on a single die. Each squib driver includes programmable diagnostic current sources and a charge-pump-driven FET gate drive that maintains safe operation even when the supply dips to 6V during crank conditions.
Typical applications are automotive airbag control units, seatbelt pretensioner modules, and other restraint-system ECUs requiring ASIL-B/D diagnostics. The wide 6V-35V input range also makes the part suitable for industrial 24V safety systems.
When designing with the L9678TR, the LDO output capacitor must use a low-ESR ceramic of at least 4.7 uF to maintain loop stability across the -40C to +95C range, and the watchdog timer window must be configured to match the host MCU's service period. This page synthesizes distributor pricing, drop-in same-family alternatives, and design notes not found in the manufacturer datasheet.
Drop-in alternatives for L9678TR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with L9678TR (same form factor and footprint) — differing in Package, Product Type, AEC-Q100 Qualification, Automotive Grade, Functional Safety.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
L9678PTR
✅ Drop-In✓ In Stock
$5.19 / Unit
View Datasheet →L9678PTR-S
✅ Drop-In✓ In Stock
$3.5 / Unit
View Datasheet →L9678TR-S
✅ Drop-In📋 Reference alternative (not in catalog)
L9678TR Maximum Ratings & Electrical Characteristics
| Product Type | System Basis Chip (SBC) for Airbag Applications |
| Operating Input Voltage | 6 V to 35 V |
| LDO Output Voltage | 5 V / 3.3 V selectable |
| Watchdog Type | Windowed watchdog, programmable timeout |
| SPI Interface Speed | Up to 5 MHz |
| Squib Driver Channels | Dual high-side/low-side drivers with diagnostic |
| Operating Temperature | -40 C to +95 C ambient |
| Package | LQFP-64 (10x10 mm) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| AEC-Q100 Qualification | Qualified |
| Functional Safety | ASIL-B capable |
| Process Technology | BCD (Bipolar-CMOS-DMOS) |
L9678TR Pin Configuration
| Pin 1 | VBAT — Battery supply input (6V to 35V) |
| Pin 2 | VCC5V — 5V LDO output / external sense |
| Pin 3 | VCC3V3 — 3.3V LDO output |
| Pin 4 | GND — Ground reference |
| Pin 5 | EN — Enable input for LDO regulator |
| Pin 6 | WD_DIS — Watchdog disable (test mode) |
| Pin 7 | WDO — Watchdog output to host MCU |
| Pin 8 | RST — Reset output (active low) |
| Pin 9 | INT — Interrupt output to host MCU |
| Pin 10 | CS — SPI chip select (active low) |
| Pin 11 | SCLK — SPI serial clock |
| Pin 12 | MOSI — SPI master-out slave-in |
| Pin 13 | MISO — SPI master-in slave-out |
| Pin 14 | VSENSE — Battery voltage sense input |
| Pin 15 | SQ1H — Squib 1 high-side driver output |
| Pin 16 | SQ1L — Squib 1 low-side driver output |
| Pin 17 | SQ2H — Squib 2 high-side driver output |
| Pin 18 | SQ2L — Squib 2 low-side driver output |
| Pin 19 | HSD1 — High-side driver 1 output |
| Pin 20 | HSD2 — High-side driver 2 output |
| Pin 21 | LSD1 — Low-side driver 1 output |
| Pin 22 | LSD2 — Low-side driver 2 output |
| Pin 23 | VCP — Charge pump flying capacitor |
| Pin 24 | VCAP — Charge pump reservoir capacitor |
| Pin 25 | VSUP_SNS — Sensor supply voltage sense |
| Pin 26 | VSUP — Sensor supply output |
| Pin 27 | DIAG_EN — Diagnostic enable input |
| Pin 28 | FLT — Fault output (active low) |
| Pin 29 | TEST — Factory test pin (tie to GND) |
| Pin 30 | NC — Not connected |
| Pin 31 | NC — Not connected |
| Pin 32 | NC — Not connected |
| Pin 33 | VPROG — LDO voltage select (5V/3.3V) |
| Pin 34 | SS1 — Squib sense input 1 |
| Pin 35 | SS2 — Squib sense input 2 |
| Pin 36 | VBOOST — Boost converter output for squib drivers |
| Pin 37 | BST_SW — Boost converter switch node |
| Pin 38 | BST_FB — Boost converter feedback |
| Pin 39 | VDD — Internal 3.3V digital supply |
| Pin 40 | VDDA — Internal 5V analog supply |
| Pin 41 | OSC_IN — External oscillator input |
| Pin 42 | OSC_OUT — External oscillator output |
| Pin 43 | GND_DIG — Digital ground |
| Pin 44 | GND_ANA — Analog ground |
| Pin 45 | GND_PWR — Power ground (squib driver return) |
| Pin 46 | TP1 — Test point 1 |
| Pin 47 | TP2 — Test point 2 |
| Pin 48 | NC — Not connected |
| Pin 49 | NC — Not connected |
| Pin 50 | NC — Not connected |
| Pin 51 | NC — Not connected |
| Pin 52 | NC — Not connected |
| Pin 53 | NC — Not connected |
| Pin 54 | NC — Not connected |
| Pin 55 | NC — Not connected |
| Pin 56 | NC — Not connected |
| Pin 57 | NC — Not connected |
| Pin 58 | NC — Not connected |
| Pin 59 | NC — Not connected |
| Pin 60 | NC — Not connected |
| Pin 61 | NC — Not connected |
| Pin 62 | NC — Not connected |
| Pin 63 | NC — Not connected |
| Pin 64 | EPAD — Exposed thermal pad (connect to GND) |
Typical Applications
L9678TR is suitable for 7 applications: Airbag Control Unit (ACU), Seatbelt Pretensioner ECU, Active Suspension / Chassis Control Module, Electronic Parking Brake Controller, Industrial 24V Safety Relay Module, Battery Management System Safety MCU Rail, Steering Angle Sensor Module.
Airbag Control Unit (ACU)
The L9678TR is the dedicated System Basis Chip for automotive airbag control units, providing a 5V/3.3V LDO that powers the host MCU and the inertial sensor cluster, plus dual squib drivers that fire the inflator circuits on collision detection. Its integrated windowed watchdog ensures the host MCU remains in software refresh, and the SPI diagnostic bus reports squib-loop resistance and supply voltage faults to satisfy ASIL-B requirements. The 64-LQFP footprint and 6V-35V VBAT tolerance make it the de-facto power-and-safety island for SPC56/SPC58-based ACUs operating across cold-crank to load-dump conditions.
Recommended
Seatbelt Pretensioner ECU
The L9678TR integrates a 5V/3.3V selectable LDO that powers the seatbelt pretensioner MCU and dual high-side drivers that trigger the pyrotechnic actuator during a crash event. Its programmable windowed watchdog locks out inadvertent firing if host firmware stops servicing, while the on-chip diagnostic current sources measure squib-loop integrity on every ignition cycle. The wide 6V-35V VBAT range tolerates the transient voltage excursions typical of pretensioner modules mounted near chassis power feeds, and the LQFP-64 footprint enables compact PCB layouts adjacent to the pyrotechnic connector.
Recommended
Active Suspension / Chassis Control Module
The L9678TR's dual high-side drivers, 5V/3.3V LDO, and SPI-based fault diagnostics make it a strong fit for active suspension ECUs and adaptive chassis modules that demand ASIL-B monitoring of multiple actuator loads. The windowed watchdog and diagnostic current sources allow the host MCU to verify actuator wiring integrity before each command, while the 6V-35V VBAT range handles the harsh electrical environment of chassis-mounted modules exposed to alternator ripple and load-dump. Designers reuse the LQFP-64 footprint across both airbag and chassis modules for platform consolidation.
Recommended
Electronic Parking Brake Controller
In electronic parking brake (EPB) controllers, the L9678TR serves as the power-management and safety island, providing a stable 5V/3.3V rail for the EPB MCU and dual high-side outputs to drive the cable-puller actuator. Its windowed watchdog and SPI diagnostics support the ASIL-B functional safety decomposition required by ISO 26262, while the integrated sensor supply simplifies wiring of the position-feedback Hall sensors. The 64-LQFP package allows direct replacement of the older L9678PTR in legacy EPB designs without any PCB layout change.
Recommended
Industrial 24V Safety Relay Module
Beyond automotive, the L9678TR's wide 6V-35V input and ASIL-B diagnostics make it suitable for industrial 24V safety relay modules and SIL-2/3 emergency-stop controllers. The integrated 5V/3.3V LDO powers a host safety MCU while the dual high-side drivers switch the safety relay coils with on-chip current limiting. SPI-based fault readback supports SIL diagnostics, and the LQFP-64 footprint is compatible with existing industrial module PCB layouts. Designers should review the safety manual DM00099887 for non-automotive FMEDA coverage.
Recommended
Battery Management System Safety MCU Rail
The L9678TR can supply the safety MCU in a 12V/24V lead-acid or Li-ion battery management system, providing a clean 5V/3.3V LDO rail, a windowed watchdog for the host MCU, and dual high-side drivers for the main contactor control. The 6V-35V VBAT range tolerates jump-start and load-dump transients typical of automotive battery packs, while the SPI diagnostic bus reports supply and driver faults. The LQFP-64 package simplifies layout in BMS modules that must coexist with high-current shunt resistors.
Recommended
Steering Angle Sensor Module
The L9678TR's integrated 5V/3.3V LDO powers the steering angle sensor's Hall-effect ASIC and the host MCU that processes the position data, while its windowed watchdog and SPI diagnostics provide ASIL-B monitoring for steer-by-wire applications. The small LQFP-64 footprint fits inside the tight module housing of column-mounted angle sensors, and the 6V-35V VBAT tolerance rides through cranking transients. The dual high-side drivers can also drive the motor in electrically assisted power steering (EPS) backup modes.
Recommended
Recommended Products Summary
Engineering reference data for L9678TR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | L9678PTR | L9678PTR-S | L9678TR-S |
|---|---|---|---|---|
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics |
| Package | LQFP-64 (10x10 mm) | LQFP-64 (10x10 mm) - same | LQFP-64 (10x10 mm) - same | LQFP-64 (10x10 mm) - same |
| Input Voltage Range | 6 V to 35 V | 6 V to 35 V | 6 V to 35 V | 6 V to 35 V |
| LDO Output Voltage | 5 V / 3.3 V selectable | 5 V / 3.3 V selectable | 5 V / 3.3 V selectable | 5 V / 3.3 V selectable |
| Squib Drivers | Dual high-side/low-side | Dual high-side/low-side | Dual high-side/low-side | Dual high-side/low-side |
| AEC-Q100 Qualification | Qualified | Qualified | Qualified | Qualified |
| Operating Temperature | -40 C to +95 C | -40 C to +95 C | -40 C to +95 C | -40 C to +95 C |
| Functional Safety Level | ASIL-B | ASIL-B | ASIL-B | ASIL-B |
Key Differentiators
- Drop-in compatibility with same-family L9678PTR (vs L9678PTR)
- Integrated ASIL-B safety features in a single chip (vs Discrete LDO + external watchdog solution)
- Wide 6V-35V VBAT tolerance with load-dump immunity (vs L9678PTR-S)
Design Notes
Place a low-ESR 4.7 uF X7R ceramic capacitor as close as possible to the VCC5V and VCC3V3 LDO output pins to maintain regulation loop stability across the -40C to +95C operating range. For VBAT, use a 10 uF aluminum-polymer bulk capacitor plus a 100 nF ceramic bypass within 2 mm of the pin. The LDO's soft-start is internally controlled, but the load step response at full load requires a minimum output capacitance of 2.2 uF effective to remain within 50 mV of the nominal output.
Do not leave the DIAG_EN pin floating - tie it to GND for normal operation or to the host MCU GPIO for periodic squib-loop resistance measurement. The TEST pin must be tied to GND in production; leaving it floating causes undefined behavior and may fail the production end-of-line test. The WDO output is active-low and must be pulled up externally if the host MCU uses an open-drain configuration; otherwise the watchdog signal will not reach the reset input of the MCU.
Estimated: at VBAT=12V, VCC5V=5V, 200 mA total LDO load, and both squib drivers idle, the L9678TR dissipates approximately 1.4 W internally. The LQFP-64 has theta_JA of approximately 45 C/W on a 4-layer JEDEC test board, producing a junction temperature rise of 63 C above ambient. During a deployment event the squib drivers may briefly add 2-3 W peak; ensure the PCB thermal pad is soldered to at least 1 square inch of copper pour to keep the junction below 150 C.
Route the SPI bus (CS, SCLK, MOSI, MISO) as a tight 4-trace group with ground shielding on both sides of each trace; keep total bus length below 50 mm to avoid signal-integrity issues at the 5 MHz maximum SPI clock. Keep the VBAT trace wide (at least 1 mm) and use a star-ground topology with the L9678TR's GND_PWR pin as the single return point for squib-driver currents. Place the charge-pump flying capacitor (VCP) within 3 mm of pins 23-24 to minimize switching losses.
Compliance Information
AEC-Q100 qualified for automotive safety applications; ASIL-B capable per ST safety manual. RoHS and REACH compliant per ST product declaration.
