MC33661 vs MC33662

[erwanmarc]

Hello,

On one of our products, we placed a MC33661 after a LINUART: everything is OK.

Because part is now obsolet and no longer available at distributors, we switched to "equivalent" MC33662.

The batch just produced doens't work for LIN functions... we changed the chip back to MC33661 and it is OK...

A quick analyze shows that there is only the Break field (13 bits).

A deeper anamyze shows there is an important differences: comparing signals on Rx and Tx lines on µc side, we see delays.

On MC33661 we have about 12µs

On MC33662 we have about 25µs

Because we operate at 20kb/s, such delay stands for 1/2 bit then the LINUART can't read back its synch field and stops operations.

Do you have such known issue on this component and a workaround?

Regards

[erwanmarc]

It looks like there is now 2 variants up-to 10 and up-to 20kbits, referin,g toe 01/2014 datasheet:

Part number selection defines the operating baud rate (33662L or 33662S for 20 kB/s and 33662J for 10 kB/s)

[erwanmarc]

After discussion with a Application - Product Definer Engineer in Toulouse, it seems that the specification fo Tx-LIN delay are no longer in last LIN specification (2.x) so focus has been made for MC33662 on EMC and only LIN-Rx delay.

I've no change to operate MC33662 on my application with my MCU LINUART bit-centric.

[erwanmarc]

According to Freescale support, this is normal: EMC improvment generates longer propagation delays...

Anyway this is a major issue in fact, despite it is better for EMC!

Indeed, the LIN UART reads back its 13 bits Break field but on the first bit there is an immediately error: information on Rx pin doesn't matches on one sent on Tx pin => Not valid Tx => Error detected.

It is the specification on LIN bus, isn't it?

LIN Transceiver is directly connectect to µc ATTiny. We placed oscilloscope on Tx line and Rx line (resp pins 4 and 1 on MC33661/2) to see the signals: 12.5µs on 33661 and 25µs on 33662.

Do anyone have an advice?

[erwanmarc]

It is confirmed that issue comes from MC33662.

To operate at 20kp/s, we have to switch back to current version of 33661 or find a chip from another supplier.

Regards