1. Introduction
This document provides a detailed technical comparison between the TJA1040T/CM,118 (now EoL) and its recommended replacement, the TJA1044CT/0Z, with a focus on hardware and software compatibility.
Our AH1308 Application Hints explicitly confirm that all Mantis-family transceivers (including the TJA1044) are drop-in replacements for the TJA1040 and TJA1042, as long as the SPLIT pin is not used in the existing design. Several functional differences nevertheless require engineering review, as detailed in the sections below.
2. Quick Reference: Key Differences at a Glance
3. Pin 5: SPLIT vs. NC
The TJA1040 provides an active VCC/2 voltage source on Pin 5 (SPLIT) in Normal mode, which is intended to be connected to the centre tap of a split bus termination network to stabilise the common-mode voltage and reduce EME. In Standby mode the SPLIT output is floating.
The TJA1044CT pin 5 is internally not bonded (NC).
The following scenarios apply:
• SPLIT pin was NOT connected in the existing design: No hardware modification required. The two devices are pin-compatible in this configuration.
• SPLIT pin WAS connected for split termination: The centre-tap capacitor should be reconnected to GND directly (passive split termination). This may cause a marginal EME difference, which should be verified against OEM requirements.
4. Wake-up Behavior (Key Functional/Software Difference)
The TJA1040 implements "basic wake-up" per the older ISO 11898-2 standard: the low-power receiver monitors the bus and asserts RXD LOW as soon as a single continuous dominant phase longer than tBUS (0.75–5 µs) is detected. No pattern is required.
The TJA1044CT implements "wake-up pattern" wake-up per ISO 11898-2:2024: a complete dominant–recessive–dominant (D-R-D) pattern must be received before RXD is asserted. Each phase must meet minimum filter requirements and the entire pattern must complete within the wake-up timeout window.
Software impact: confirm the node is woken using a standard CAN wake-up pattern rather than a single dominant edge. Most CAN stacks already generate a WUP, but this should be verified for the end application.
5. TXD Dominant Time-out
Both devices provide the TXD dominant time-out fail-safe (the transmitter is disabled if TXD is held LOW). The function behavior is identical, but the timing parameters differ:
The TJA1044 time-out is longer, which lowers the minimum supported bit rate. This is only relevant for very-low-bit-rate designs.
6. Standby-to-Normal Mode Transition Time
The transition time from Standby to Normal mode is longer on the TJA1044CT. If the µC firmware drives STB LOW and immediately begins CAN transmission without a guard delay, the first transmitted frames may be corrupted or lost when using the TJA1044CT.
Recommendation: ensure the µC waits a minimum of 47µs after asserting STB LOW before initiating any CAN frame transmission.
7. Undervoltage Detection and OFF Mode
The TJA1040 has two operating modes (Normal, Standby). When VCC is lost, pins TXD/STB/RXD become floating, with no defined bus disengagement.
The TJA1044CT introduces a third operating mode, OFF, with two undervoltage detection thresholds on VCC:
This is a fail-safe improvement. The bus is properly disengaged (zero load) when VCC is insufficient, preventing an unpowered node from affecting bus communication. No software change is required to benefit from this feature.
8. VCC Range and Additional Electrical Improvements
The TJA1044CT offers several electrical improvements over the TJA1040 that are fully backward compatible and require no design changes:
9. Summary of Required Actions
