This part was taken from a Motronic M1.7.3 engine control unit (ECU), which was commonly used on 1.6L & 1.8L 4-cylinder BMWs of the mid-E36 generation. While this chip was likely used on a number of ECUs, the specific one in this case had Bosch PN 0 261 203 661.

Functionally, this chip provides a number of analog functions and some digital ones. It is a custom Bosch part.

- Buffers the ignition coil dwell (primary coil charging) signal from the MCU to the IC that drives the bases of the high current switching transistors

- Takes the MCU's TTL UART Rx+Tx signals, and handles their conversion to the bidirectional single-wire K-Line interface used for automotive diagnostics

- Filters and amplifies the analog output of a narrow-band oxygen sensor, which is fed to an ADC input on the MCU

- Filters the crankshaft sensor (variable reluctance type) signal, providing zero-crossing detection and offset adaptation, and ultimately outputs a TTL signal to the MCU which is used for sensing crankshaft rotation speed and angular position

Label (top):

[Bosch Logo]
30318 (Bosch internal PN)
08/0896
A0887.1

Decap Steps:
Selective crushing with bench vise

Capture Details:
Imaging device: Keyence VHX-2000
Magnification: 200X, 500X

Markings:
[Bosch Logo]
J53B
CJ53B (likely a reference to the commercial PN used by Bosch)

Imaged with the clear conformal coating left on the die (200X):

Imaged after scraping the conformal coating off, which damaged the metal layer (500X):

Note: This is a ~5X downsampled version of the original image. A full resolution version (16MB) can be provided. On the to-do list…