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Technical Specifications
Parameter Specification
Function Type System-Basis Chip (SBC)
Technology ST proprietary BCD mixed-signal technology
Operating Temperature Range -40°C to +150°C
Package Type HSSOP-36 / PowerSSO-36 (with exposed thermal pad)
Package Dimensions Approx. 15.9 mm × 7.5 mm (typical PowerSSO-36 dimensions)
Pin Pitch 0.8 mm (typical PowerSSO-36 pitch)
RoHS Status RoHS compliant
Power Management Functions
Parameter Specification
Main Voltage Regulator Precision pre-regulated 5V output (Vdd), output current > 400 mA
Sensor Supply Regulators Two protected sensor supply voltage regulators, tracking Vdd
Vbat Protected Switch Output Battery voltage protected switch output
Multifunction Reset Flag System reset function
Power Latch Enable Pin Enable pin for power latch function
Communication Interfaces
Parameter Specification
High-Speed CAN Bus Transceiver High-Speed CAN Bus Transceiver
Dual Bi-directional Serial Lines Dual Bi-directional Serial Lines (K-line, ISO K-line interface)
Sensor Interfaces
Parameter Specification
Variable Reluctance Sensor Interface Configurable Variable Reluctance Sensor Interface
Hysteresis Selection High/Low Hysteresis Selection
VRS Diagnosis Function VRS Diagnosis Function
Driver and Analog Functions
Parameter Specification
Single-Channel Protected Low-Side Driver Output Single Protected Low-Side Driver Output
Typical Load Fuel Pump Relay
Fully Differential to Single-Ended Op-Amp Full Differential to Single-Ended Op-Amp
Programmable Gain 4 programmable gain settings
Typical Application Knock Sensor Interface
Protection Functions
Function Description
Thermal Protection Thermal protection during short-circuit events
Overcurrent Protection Independent overcurrent protection for each output channel Over-voltage protection Power system over-voltage protection
Under-voltage lockout System under-voltage detection and reset
---
Pin Definitions (HSSOP-36 / PowerSSO-36)
HSSOP-36 Package Features: 36-pin small-outline package with an exposed thermal pad on the bottom; must be soldered to the PCB ground plane to ensure heat dissipation.
Pin Area Function Category Typical Functions
1-8 Power and Ground Vbat, Vdd, GND, Thermal Pad
9-16 Voltage Regulators Main 5V regulator output, sensor power output, decoupling capacitor connections
17-24 Communication Interfaces CANH, CANL, K-line 1, K-line 2
25-30 Sensors and Drivers VRS input, VRS configuration, low-side driver outputs
31-36 Analog and Reset Op-amp differential inputs (+/-), op-amp output, gain configuration, reset output, enable input
> Note: Please refer to the official STMicroelectronics datasheet for specific pin assignments. The exposed thermal pad must be soldered to the PCB ground plane to ensure proper chip heat dissipation and electrical grounding. ---
Typical Application Circuit
1. Engine Management ECU Core Module
```
+Vbat (+12V Car Battery)
│
├──┬─────────────────────────────┐
│ │ │
│ L9741 (HSSOP-36) │
│ │ │
│ Vbat ────────────────────────┤→ Battery Input
│ │ │
│ Vdd (5V/400mA) ──────────────┤→ MCU Core Power Supply
│ │ │
│ Sensor Supply 1 ─────────────┤→ Sensor Power (Tracks Vdd)
│ Sensor Supply 2 ─────────────┤→ Sensor Power (Tracks Vdd)
│ │ │
│ CANH ────────────────────────┤→ CAN Bus High
│ CANL ────────────────────────┤→ CAN Bus Low
│ │ │
│ K-line 1 ────────────────────┤→ Diagnostic Interface 1
│ K-line 2 ────────────────────┤→ Diagnostic Interface 2
│ │ │
│ VRS Input ───────────────────┤→ Crankshaft Position Sensor
│ VRS Config ──────────────────┤→ Hysteresis/Diagnostic Config
│ │ │
│ Low-side Driver Output ──────┤→ Fuel Pump Relay
│ │ │
│ Op-Amp Diff. Input + ────────┤→ Knock Sensor +
│ Op-Amp Diff. Input - ────────┤→ Knock Sensor -
│ Op-Amp Output ───────────────┤→ MCU ADC
│ Gain Config ─────────────────┤→ Gain Selection (4 Levels)
│ │ │
│ Reset Output ────────────────┤→ MCU Reset
│ Enable/Latch ────────────────┤→ Power Management Control
│ │ │
│ GND ─────────────────────────┤→ Ground
│ Thermal Pad ─────────────────┤→ GND (Must be soldered)
│ │
└────────────────────────────────┘
```
- Features: Single-chip implementation of engine ECU power management, communication, sensor interfacing, and driving functions; reduces external component count. - Thermal Pad: The exposed pad on the bottom of the HSSOP-36 package must be fully soldered to the PCB ground plane to ensure proper heat dissipation and grounding.
2. Fuel Pump Control and Knock Detection Application
```
+Vbat (+12V)
│
├──┬─────────────────────────────┐
│ │ │
│ L9741 (HSSOP-36) │
│ │ │
│ Vbat ────────────────────────┤→ Battery Input
│ │ │
│ Low-side Driver Output ──────┤→ Fuel Pump Relay Coil
│ │ │
│ Relay Contacts ────────────┐ │
│ │ │ │
│ +12V ────────────────────┤ │
│ │ │ │
│ Fuel Pump Motor ───────────┘ │
│ │ │
│ Knock Sensor ──────────────┐ │
│ (Piezoelectric) │ │
│ │ │ │
│ Op-Amp Diff. Input + ──────┤ │
│ Op-Amp Diff. Input - ──────┤ │
│ │ │ │
│ Op-Amp Output ─────────────┤→ MCU ADC (after band-pass filtering)
│ (Configurable Gain) │
│ │ │
│ GND/Thermal Pad ─────────────┤→ Ground
│ │
└────────────────────────────────┘
```
- Features: The low-side driver directly drives the fuel pump relay; the operational amplifier conditions the knock sensor signal for MCU analysis of ignition advance angle.
3. Crankshaft Position Detection and CAN Communication
```
L9741 (HSSOP-36)│
├──┬─────────────────────────────┐
│ │ │
│ VRS Input ───────────────────┤→ Variable Reluctance Sensor (Crankshaft)
│ │ (Signal Conditioning) │
│ VRS Configuration ───────────┤→ High/Low Hysteresis Selection
│ │ │
│ Conditioned Signal ──────────┤→ MCU Timer Capture
│ (Digital Output) │
│ │ │
│ CANH ────────────────────────┤→ Vehicle CAN Network
│ CANL ────────────────────────┤→ Vehicle CAN Network
│ │ │
│ K-line 1 ────────────────────┤→ OBD Diagnostic Tool
│ │ │
│ GND/Thermal Pad ─────────────┤→ Ground
│ │
└────────────────────────────────┘
```
- Features: The Variable Reluctance Sensor (VRS) interface directly processes crankshaft/camshaft position signals, eliminating the need for an external comparator; the CAN bus enables communication with the vehicle network. ---
Key Characteristics
Parameter Condition Typical Value
Vdd Output Voltage Full temperature range 5.0 V ± 2%
Vdd Output Current - 400 mA
Sensor Supply Tracking Accuracy Relative to Vdd ± 1%
CAN Bus Rate High-speed CAN 125 kbps – 1 Mbps
K-line Baud Rate Standard ISO 10.4 kbps
VRS Input Sensitivity Adjustable hysteresis High / Low hysteresis
Low-side Drive Current Fuel pump relay Typ. 200–500 mA
Op-Amp Gain Setting 4-level programmable 1x, 2x, 5x, 10x (typical)
Operating Current All functions active 50–100 mA
Standby Current Sleep mode < 100 µA
Thermal Shutdown Threshold Chip temperature 150°C – 175°C
---
Alternative Models and Competitor Products
Model Manufacturer Key Differences
L9741 STMicroelectronics Original model, HSSOP-36/PowerSSO-36, Engine Management System SBC
L9741XP STMicroelectronics Improved version, PowerSSO-36, with exposed pad, enhanced thermal dissipation
L9741TR STMicroelectronics Tape & Reel version, HSSOP-36
L9758 STMicroelectronics Multi-function power supply, engine control, different package
L9758XP STMicroelectronics PowerSSO-36, multi-function power supply
L9758TR STMicroelectronics Tape & Reel version
L9777B STMicroelectronics Related model, low-power voltage regulator
L9790 STMicroelectronics Related model, LCD calculator CMOS LSI
TLE6244 Infineon Fuel injector driver IC, HQFP-64, different architecture
TLE8880 Infineon Engine Management System SBC, higher level of integration
MC33910 NXP Automotive System Basis Chip (SBC), CAN/LIN UJA1078 NXP Automotive System Basis Chip (SBC), CAN/LIN
---
Precautions
- Compatibility: The L9741 (HSSOP-36) is a dedicated engine management system chip. When replacing it, ensure the following:
- Package matches exactly (HSSOP-36 / PowerSSO-36, 15.9 × 7.5 mm, 0.8 mm pin pitch).
- Pin definitions are compatible with the ECU circuitry.
- Functional configuration (VRS hysteresis, op-amp gain, CAN termination resistor) is matched via software.
- Priority should be given to the same model or the L9741XP (an improved thermal dissipation version).
- Installation Instructions:
- HSSOP-36 is a surface-mount package with an exposed bottom thermal pad; reflow soldering equipment is required.
- Thermal Pad: The exposed bottom pad must be fully soldered to the PCB ground plane to ensure proper heat dissipation and electrical grounding. Adding multiple thermal vias connecting to the internal ground plane is recommended.
- Soldering Temperature: Reflow peak temperature of 260°C for ≤ 10 seconds; manual soldering is not recommended due to the risk of damage.
- ESD Protection: BCD mixed-signal chips are ESD-sensitive; wear an anti-static wrist strap and use an anti-static mat during handling.
- Decoupling Capacitors: Place a combination of 10µF and 100nF decoupling capacitors close to the Vdd pin.
- CAN Bus: Connect a 120Ω termination resistor between CANH and CANL; pay attention to differential impedance during PCB routing.
- K-line: A series protection resistor is required to prevent damage from overvoltage caused by diagnostic tools.
- Thermal Management: For high-current applications (>200mA), ensure the PCB copper area is ≥ 10 cm² or add thermal vias connecting to internal layers. - Troubleshooting:
- No Vdd output: Check Vbat input, enable pin, and thermal shutdown status.
- CAN communication failure: Check termination resistors and bus voltages (CANH: 2.5V–3.5V, CANL: 1.5V–2.5V).
- No VRS signal: Check sensor connections, hysteresis configuration, and input pin voltage.
- No low-side driver output: Check input signals, load connections, and overcurrent protection status.
- Abnormal op-amp output: Check gain configuration, input common-mode range, and output load.
- Frequent system resets: Check Vdd load current, undervoltage thresholds, and power supply ripple.
- Chip overheating: Check thermal pad soldering quality, PCB thermal design, and ambient temperature.
- Repair Recommendations:
- Inspect peripheral components before replacement: decoupling capacitors, termination resistors, and protection diodes.
- Perform functional tests after replacement: power supply output, CAN communication, sensor signals, and driver outputs.
- Check VRS and knock sensors for damage to rule out external faults.
- Inspect thermal pad soldering quality to ensure no cold joints or voids.
- Operations should be performed by professional automotive ECU technicians to ensure correct software configuration.
- Technical Support: For further technical support, please refer to the STMicroelectronics L9741 application notes or contact an authorized distributor.
---
Summary
The L9741 HSSOP-36 is a System-Basis Chip (SBC) for engine management systems manufactured by STMicroelectronics. It utilizes the HSSOP-36 (Heat Sink Small Outline Package-36) package and is based on ST's proprietary BCD mixed-signal technology. The chip integrates a multifunctional 5V voltage regulator (400mA), two sensor power supplies, a high-speed CAN bus transceiver, dual K-line interfaces, a variable reluctance sensor (VRS) interface, a single-channel protected low-side driver, and a programmable-gain (4 settings) differential operational amplifier. It operates within a temperature range of -40°C to +150°C. The design of the exposed thermal pad at the bottom of the HSSOP-36 package ensures excellent thermal performance, enabling the device to withstand the harsh thermal environment of the engine compartment.
Serving as a core System Basis Chip (SBC) in automotive engine management ECUs, the L9741 provides comprehensive functionality—including power management, communication interfaces, sensor signal conditioning, and driver outputs—thereby significantly reducing the external component count and enhancing system reliability. As an automotive-grade SBC from ST, the L9741 features high-precision power supplies, robust protection mechanisms, and a wide operating temperature range, making it ideal for gasoline and diesel engine control systems....one of the mainstream solutions in the system. Its HSSOP-36 package balances thermal performance, PCB footprint, and automated assembly requirements, making it an ideal choice for highly integrated power management chips in automotive electronics.
