The ST Microelectronics L9101 is a IC that can be found in many vehicle control units built by Magneti Marelli. It appears to have been used only by Magneti Marelli. A datasheet for the L9101 cannot be found. Mouser lists the part, but with the attributes "not available" and "discontinued". The L9101 shown here was retrieved from an ECU.
The circuit around the L9101 in the ECUs shows which functions have been integrated. The module is usually used to read inductive speed sensors, such as those found on the crankshafts of combustion engines. The L9101 is also a transceiver for the K and the L line. These two lines are part of the standardized diagnostic interface via which the status of a vehicle can be read out.
It does not seem particularly obvious to integrate a sensor interface and a bus transceiver in one ASIC. However, there were obviously good reasons to do so. In automotive ECUs, attempts have always been made to integrate circuits and combine them into larger parts. As these are often very specialized functions and circuits, ASICs are created that are often only used in the automotive sector.
The L9101 contains a 2,43mm x 1,85mm die. This image is also available in higher resolution:
https://www.richis-lab.de/images/ecu/05x02XL.jpg (19MB)
In addition to the ST logo, the die also shows some character strings. CL001B could be an internal project designation. The letter B could then be a revision. However, this is pure speculation. As described in the context of the NE555 from ST Microelectronics, character strings such as 800C5 appear to describe a process technology or a technology node (
https://www.richis-lab.de/555_1.htm). The IC is based on a bipolar process with one metal layer. The numbers 92 could stand for the year 1992.
The reference potential is distributed by a wide frame structure (blue). The L9101 is supplied with +12V (yellow) and +5V (red). Strictly speaking, the +12V potential is the so-called terminal 30, which can also supply slightly higher voltages.
The die clearly shows a division into two parts. Apart from the supply potentials, these two parts have no electrical connection.
Large picture:
https://www.richis-lab.de/images/ecu/05x08XL.jpgThe circuit can still be analyzed relatively well. Most of the inputs and outputs have protective diodes, which are not shown here.
The upper circuit, the left part on the die, consists of three blocks.
The two blocks on the left are the receiver circuits for the L and K lines. They have almost the same structure. A differential amplifier receives the signal. In contrast to the rest of the circuit, the differential amplifier is supplied from the 12V potential. This is necessary because the high level of the input signal is 12V. The circuit around Q74 and Q76 ensures that the 12V supply is only active when a 5V potential is also present. This ensures that no current is drawn from the permanently applied 12V potential as long as the ECU is not active.
The reference potential of the differential amplifier is supplied by a voltage divider, which is also supplied from the 12V potential. This makes sense as the high level on the bus fluctuates with this potential. The reference potential is influenced by the output signal of the differential amplifier via a transistor. This results in the hysteresis required for evaluating the bus signals. This is followed by a simple output stage. In addition the inverted level of the K line is routed to the third circuit block.
The right-hand block is the transmitter for the K line. Here, too, there is a differential amplifier at the input. The reference level is obtained from the 5V potential. The open collector output of transistor Q53 on the far right is ultimately controlled. If a high level is present at the input, the output becomes inactive. Transistor Q50 ensures that this happens directly and without delay.
The output of a low level is much more complex. If the input changes to a low level, the differential amplifier at transistor Q46 also outputs a low level. This causes all the transistors connected there to switch off. As a result, transistors Q51, Q50 and Q55 are inactive in the output area. The current through R59 activates the driver Q54 and thus the output transistor Q53.
The low level represents the dominant state on the K line. A malfunction of an ECU could therefore easily block the entire bus by outputting a permanent low level. For this reason, the L9101 only allows short low pulses. If the output is switched active, the capacitor C5 is simultaneously charged via the current source Q61. The voltage divider R63/R64 determines the maximum voltage. As soon as the capacitor voltage approaches this voltage, current flows trough transistor Q60. At the same time, the current from current source Q63 flows through transistor Q58. This in turn activates transistor Q55, which finally deactivates driver Q54 and thus also the output transistor.
The signal from the receiver circuit of the K line controls the transistor Q62. This link ensures that the transmitter remains deactivated if a low level is already present on the bus. Transistor Q56 represents a further path that can deactivate the output. This transistor is controlled via a chain of five Z diodes that are connected to the 12V potential. As these are emitter-base paths, it can be assumed that the breakdown voltage is in the range of 5-6V. This means that the output is deactivated as soon as the 12V potential rises above 25-30V.
The second part of the L9101 enables the evaluation of an inductive speed sensor.
One challenge when evaluating an inductive speed sensor is that the level changes significantly with the speed. The datasheet for the Bosch IS-C speed sensor clearly shows this relationship. As the signal is generated by induction, it is also not a clean square-wave signal, but rather sharp pulses. The environment often adds considerable interferences, which further complicates the evaluation. Nevertheless, the speed must also be detected in transient states of the motor. In addition, the gear to be evaluated usually has a larger gap at one point. This difference must be evaluated in order to determine the current angle of the motor.
Pins 6 and 7 are the inputs for the speed sensor. They lead to two symmetrical paths that are reminiscent of a differential amplifier. However, the two lines are merely a signal adjustment. The circuit section around the transistors Q38-Q40 limits the level of the input signal.
The circuit around the transistors Q36/Q37 and the circuit around the transistors Q43/Q44 control the transistor pairs at the upper and lower ends of the two strings and ensure a certain quiescent current. This type of quiescent current generation seems unusual. It probably has special advantages here.
The modified signal from the speed sensor is finally passed on to the next stage of signal processing via transistors Q32/Q33.
After signal matching, the signal passes through a voltage amplifier stage whose output is the transistors Q20/Q21. The circuit section around Q22 appears to be a current limiter. This is followed by the output stage, which outputs the processed signal at pin 10.
The potential at transistor Q24 also controls the current source Q15 by diverting its supply via Q13. The current output by Q15 is fed back to the input, where it provides positive feedback. This results in the desired comparator effect.
In addition to the current source Q15, the circuit on the far right represents another positive feedback. Here, transistor Q8 feeds the current into the input. The amount of current is defined by the current sink Q5. A large voltage divider supplies the potential that controls the current sink. A resistor with an earth reference must be connected to pin 8. The size of the resistor determines how much current flows through the transistor Q5.
Transistors Q1 and Q2 determine whether the current of the current sink is mirrored to the input or not. They can accept the current and thus divert it. Q1 is controlled by the output potential at pin 10. Q2 can be activated by the evaluating microcontroller via pin 9.
The L9101 thus offers the option of setting the hysteresis of the comparator via an external resistor and also switching it via a microcontroller. As already described, the evaluation of an inductive speed sensor is challenging. The variability is a great advantage here.
The module shown here on the left is clearly labeled differently, but contains the same design. There are no recognizable differences. The L9101 on the right was purchased new from China. It is very pleasing that this is apparently an original part.
https://www.richis-lab.de/ECU05.htm