133 lines
7.0 KiB
Markdown
133 lines
7.0 KiB
Markdown
# General-Purpose Digital Output Module
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## Purpose
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This module defines the generic harness-connected digital-output classes for
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NeoECU V1. It does not cover the dedicated ignition and injector power stages.
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Connector positions, channel count, and the assignment of vehicle functions
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remain open until packaging and connector design.
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Two non-interchangeable output classes are provided:
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- protected 5 V high-side logic outputs for external electronic-control inputs;
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- protected battery-domain low-side outputs for relays, solenoids, and other
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inductive loads.
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Firmware assigns a compatible vehicle role and reported polarity to a channel;
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it cannot turn one electrical class into the other. A starter-enable function
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may use either class only when the external starter interface accepts it.
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## Protected 5 V logic outputs
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Use the automotive-qualified TI `TPS4H000-Q1` quad smart high-side switch.
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It is supplied from `+5V_AUX`, not directly from `+5V_MAIN`.
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- `+5V_AUX` isolates an external logic-output fault from `+5V_MAIN`, the MCU,
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and the sensor-excitation rail.
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- Each channel is active high: when commanded on, it sources `+5V_AUX`.
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`R_OUT_PD` holds the connector output low when the channel is off or the ECU
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is unpowered. This is a protected high-side output with a passive low state,
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not a true push-pull stage.
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- `R_IN_PD` is an external pull-down at the IC input. It holds the output off
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while the MCU is reset, booting, unpowered, or has not deliberately taken
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control. MCU internal pulls are not a substitute.
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- Set each channel's current limit to the TPS4H000-Q1 minimum configured value
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of 100 mA. This is the intended maximum output current for this logic-output
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class; the `+5V_AUX` eFuse limit must be selected consistently with the
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populated channel count and simultaneous-fault policy.
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- Use the IC's diagnostic/current-sense variant as appropriate for the MCU
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interface. Per-channel fault reporting is useful but open-load reporting is
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optional for generic logic commands.
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### Logic-output connector protection
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Place `TVS_LOGIC_OUTx` at the connector side of each output, with a short,
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low-inductance return to the protected output-ground reference. Select its
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working standoff above the maximum `+5V_AUX` voltage and its worst-case dynamic
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clamp below the TPS4H000-Q1 output-pin limit with margin.
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The TVS absorbs transient events. It is not sized to dissipate a sustained
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misconnection to `VBAT_PROT`; the TPS4H000-Q1's off-state short-to-battery
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detection and fault behaviour must handle that case. Confirm its unpowered
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output behaviour and the completed TVS network against the actual connector
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fault and transient specification before schematic freeze.
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## Protected low-side outputs
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Use the automotive-qualified Infineon `TLE9104SH` smart quad low-side switch.
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It drives battery-domain loads supplied from `VBAT_PROT`.
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- The TLE9104SH supplies active inductive-load clamping, configurable
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overcurrent protection, short-circuit and thermal protection, direct channel
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inputs, and SPI diagnostics.
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- `VS` is supplied from `VBAT_PROT`; use the documented logic supplies so the
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MCU-facing interface is referenced to `+3V3_MAIN` while the driver itself is
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supplied from the internal 5 V rail. Decouple both supply domains locally at
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the IC.
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- `R_EN_PD` holds `EN` inactive through power-up and MCU reset. `R_IN_PD` on
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every direct input holds its channel off. Firmware may enable outputs only
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after the required reset, SPI configuration, and diagnostic checks have
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completed.
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- Use the diagnostic interface to identify overcurrent, overtemperature,
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short-to-battery, short-to-ground, and—where useful—open-load faults. The
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final retry, latching, reporting, and output-inhibit policy is firmware work
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and remains open.
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- Define `OUT_PGND` as a high-current return domain. It must remain separate
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from `DGND`, sensor return, injector return, and ignition return until the
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deliberate power-entry star connection.
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### Sink-output connector protection
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The TLE9104SH's internal active clamp is the primary turn-off path for
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inductive loads. Provide a connector-side transient-protection footprint for
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each sink output, but select and place any external TVS only after calculating
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the load energy, harness transient environment, and desired release time. An
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incorrect low-voltage clamp can bypass the driver's intended inductive clamp,
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increase TVS dissipation, or slow a relay/solenoid release.
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The final protection network shall keep the output pin within its validated
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limit for connector transients and for an externally powered load while the
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ECU is off. It shall not back-power the TLE9104SH logic supply, `+3V3_MAIN`,
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or `+5V_AUX`.
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## Default state and fault behaviour
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| Condition | Logic output (`TPS4H000-Q1`) | Sink output (`TLE9104SH`) |
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| --- | --- | --- |
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| MCU reset or boot | `R_IN_PD` holds the channel off; `R_OUT_PD` holds the connector low. | `R_EN_PD` and `R_IN_PD` keep every channel open. |
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| ECU unpowered | Output is not actively driven; connector protection and the IC must tolerate the assigned external-fault case without rail back-power. | Output is open; externally powered loads and connector faults must not back-power ECU logic. |
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| Output short/overload | Per-channel current limit and thermal protection act; `+5V_AUX` eFuse limits the aggregate branch. | Per-channel overcurrent/thermal protection acts and status is reported through SPI. |
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| Inductive turn-off | Not an intended load class. | Internal active clamp controls load-current decay; any external TVS is coordinated with it. |
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## Validation and open items before schematic freeze
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1. Confirm the output connector transient/ESD and sustained miswiring cases,
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including externally applied battery voltage while the ECU is off.
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2. Select `TVS_LOGIC_OUTx` by worst-case dynamic clamp and pulse rating, not
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nominal voltage marking. Confirm it does not conduct at the maximum
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`+5V_AUX` voltage.
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3. Select `R_OUT_PD` from the external logic-input leakage, required low level,
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and permitted static current when the output is high.
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4. Select the `+5V_AUX` eFuse threshold and TPS4H000-Q1 channel-limit setting
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together; 100 mA per active channel is the maximum intended logic-output
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current.
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5. For each sink load, establish steady current, inrush, inductance, stored
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energy, required release time, PWM requirement, and thermal/copper limits.
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6. Calculate whether an external sink-output TVS is required and verify that it
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complements rather than overrides the TLE9104SH active clamp.
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7. Define the firmware diagnostic and recovery policy, and identify any output
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assignment that needs an additional hardware permit gate.
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## References
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- [TPS4H000-Q1 product page and datasheet](https://www.ti.com/product/TPS4H000-Q1)
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- [TLE9104SH product page and datasheet](https://www.infineon.com/cms/de/product/power/smart-power-switches/multichannel-spi-switches-controller/flex-multichannel-spi-low-side-power-switch/tle9104sh/)
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