Custom Teensy 4.1 Prototype Guidance

Camthomp

Member
Hello!

I am working on integrating a Teensy 4.1 in to my project and I am designing my own board and I have some questions about components that are not easy to get/out of stock.

Currently I am working on the components that are labeled D1 and D2 on the schematic. I notice that they have been replaced with the BAS40-05V part. I am wondering if the BAT54CDW-7-F would also function as a suitable replacement?

TIA!
 
bas40-05.pngbat54cdw.png
Do you think they look even similar?
 
If you want the same circuit as Teensy 4.1 but you can use a larger PCB, using 2 SOT-23 package dual diodes would be fine. The electrons really don't care if the 3 diodes in the circuit are physically located in 2 separate plastic packages.

If you have no need for VBAT to connect a coin cell, you only need 1 pair of diodes.

But if you need a close replacement for BAS40-05V which is used on Teensy 4.1, the best alternative is Panjit BAT54CTB6_R1_00001. As of today, Mouser has many in stock.

https://www.mouser.com/ProductDetail/Panjit/BAT54CTB6_R1_00001?qs=sPbYRqrBIVkQqn0vfUVY5Q==

If you want a single diode package but you wish to optimize for best availability from multiple companies, the same 4 diode configuration is available from multiple manufacturers in a slightly larger SOT-363 package. BAS70DW-05-7-F is just 1 example, which is also in stock at Mouser.

https://www.mouser.com/c/?q=BAS70DW-05-7-F

I believe the BAT54CDW-7-F part you mentioned is one of those many similar diode arrays in 6-pin SOT-363 package. To answer your original question about BAT54CDW-7-F, yes, based on the datasheet (but not actual testing) I'm pretty confident BAT54CDW-7-F should work.
 
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Good to hear, thank you for the information!

Side bar question:
The chip labeled U6 (DP83825) is only needed if I am going to be using ethernet, correct?
 
Confirm, U6 is not needed if you never use ethernet.

TEENSY41_NE is the exact same board as TEENSY41, except U6, R3, R4 are not placed during manufacturing, and during product testing the test fixture is configured to not perform MDIO and loopback testing on the ethernet hardware.
 
Excellent! Additionally, is the U5 chip (TPD3S014) is only needed for the USB Host pins that are present only on the 4.1 and not the 4.0, correct?
 
Excellent! Additionally, is the U5 chip (TPD3S014) is only needed for the USB Host pins that are present only on the 4.1 and not the 4.0, correct?

yes, seems that (TPD3S014) is the vHost power control switch.

And - wow - 12 I/O pins feeding the ethernet chip [B1_04-15] brought out and then not used. Recall the T_4.1 beta hardware comment about the need for 12 pins for PHY.
 
Yup, 12 pins. Ethernet RMII uses 8 pins for data (or only 7... RXERR isn't strictly needed as the ethernet CRC check can discard erroneously received packets) and 2 for hardware config & control. Optional signals are used for hardware reset and low power control. Probably could have used only 7 signals. Today we're not really using the MDIO control signals much. As far as I know, the hardware reset and low power signals haven't really been needed.

But back in late 2019 when I designed Teensy 4.1, having the optional signals connected seemed like a much lower risk approach. Wiring more signal between the chips also costs a lot less PCB real estate than adding resistors to various pins to configure the PHY chip.

And also yes, TPD3S014 controls USB host power.
 
I really would not recommend trying to solder anything onto the unused U6 chip location. It's too close to the main chip. BGA chips can take a lot of heat uniformly applied, but they're not so good at withstanding a temperature gradient.
 
I think I have all the base components added to my schematic for a base version of the Teesny 4.1. I am missing the SD card slot as I am still deciding on a socket for it.

Please keep in mind, I am new at this and didn't get any formal training or schooling for schematic design. I may have not used standard practices or design patterns. Is it a mess? Yes! But I designed it in a way that I can read it :D

If I am missing anything major, please let me know!

teensy_4_1_base_hmezzw.png
 
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