NeoECU-Hardware/Architecture/IO_MODULES/INJECTON.md

Injector Output Module

Purpose

This module drives one conventional high-impedance/saturated fuel injector. It uses the STMicroelectronics VNL5050S5-E protected low-side switch (VNL5050S5TR-E for tape-and-reel assembly).

The driver provides an integrated power MOSFET, inductive-load clamp, current and power limiting, thermal protection, off-state open-load detection, and an open-drain status output. It is not a peak-and-hold injector driver; a low-impedance injector requires a different architecture.

Power path

VBAT_PROT --> injector positive terminal --> injector coil --> VNL5050 DRAIN
                                                                  |
                                                           internal low-side MOSFET
                                                                  |
                                                                SOURCE --> INJ_PGND --> power-entry ground

• The injector's positive terminal connects to VBAT_PROT; its negative terminal connects to DRAIN.
• SUPPLY connects to +5V_MAIN, the internal logic rail. Place local decoupling from SUPPLY to SOURCE, including a nearby 100 nF ceramic capacitor.
• The VNL5050S5-E provides a 41-52 V drain-source clamp for inductive turn-off. Injector current-decay/closing time must be verified using the actual injector inductance and resistance.
• Do not add a conventional flyback diode across the injector; it would slow its current decay and closing response.

Command path

INPUT is active high. It receives only the hardware-permitted injector command defined by the dead-man interlock.

SAFE_INJECTOR_SIG --> 1 kOhm Rprot --> INPUT
                                         |-- 10 kOhm ---------> INJ_PGND
                                         `-- low-capacitance
                                             Zener clamp ------> INJ_PGND

SAFE_INJECTOR_SIG = ENGINE_PERMIT AND MCU_INJECTOR_SIG

SAFE_INJECTOR_SIG is 5 V logic and therefore provides substantial margin over the VNL5050S5-E's 2.1 V minimum input-high level. The 1 kOhm Rprot resistor follows the manufacturer's protection approach. The 10 kOhm pull-down is placed on the driver side of Rprot; it holds INPUT low if the permission logic is unpowered, disconnected, or during power sequencing.

Fit the low-capacitance Zener clamp directly at the VNL5050S5-E INPUT pin, on the driver side of Rprot. Its return is the local INJ_PGND/SOURCE reference, not remote DGND. Select its clamp voltage to tolerate the valid 5 V command high while limiting coupled positive transients at the power-IC pin.

When ENGINE_PERMIT is removed, SAFE_INJECTOR_SIG goes low and turns the injector output off. This is the hardware shutoff path; firmware also clears pending injection events when it observes a dead-man release.

Status diagnostic

STATUS is an open-drain diagnostic output. It is read by the MCU through a 1 kOhm protection resistor and a +3V3_MAIN pull-up.

+3V3_MAIN pull-up --> MCU-side status node --> 1 kOhm Rprot --> STATUS

The 3.3 V pull-up is within the pin rating and provides a safe MCU logic level. The diagnostic path supports off-state open-load detection and indicates over-temperature shutdown. The VNL5050S5-E protects against short circuit and current overload internally, but its single STATUS pin does not provide a separate, unambiguous MCU-readable short-circuit/current-limit indication.

Ground and layout

Define INJ_PGND as the injector module's high-current return domain.

VNL5050 SOURCE --> short, low-impedance INJ_PGND copper --> power-entry ground star

• INJ_PGND runs directly to the power-entry ground star, where it joins the battery return, IGN_PGND, DGND, and sensor return domains.
• It must not share copper with those other returns before the star point.
• SOURCE is both the MOSFET power return and the driver's logic reference; unlike the ignition driver, this part has no separate Kelvin-sense ground pin. Keep the SUPPLY-to-SOURCE decoupling loop compact and the command and status traces away from the DRAIN switching node.
• Provide the drain copper area required by the package thermal guidance.

Remaining validation before schematic freeze

1. Measure injector coil resistance and obtain its part number/datasheet.
2. Confirm that the injector is high impedance and that its peak current, stored energy, and turn-off time fit the VNL5050S5-E limits.
3. Verify output-stage temperature using the actual injector duty cycle, board copper area, and enclosure conditions.
4. Validate injector opening/closing timing, diagnostic behavior, and ignition noise immunity on hardware.