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Hi All,
I'd like to design '4-SPI' & '1-Reset' using level shifter.
And, in that web page ; TXB-series is proper to SPI & SD. TXS-series is proper to I2C.
But '1-Reset' is concerned.
Recommend a suitable part me, please, ASAP.
Best Regard,
Inho Jeon
For unidirectional signals, you should consider using unidirectional or direction-controlled voltage translators.
How many in each direction? And what are the voltages?
Hi Emrys,
Thank you for your reply.
I'm sorry for writing two questions in same subject.
I answer your questios below this.
On my schematics, R10 & C41 is need to delay time for system power on.
'OLED_RST\' is for optional event of OLED display. So, On stable conditions 'OLED_RST\' is high until power is lost.
'OLED_RST\' is from 3.2V(MCU) to 1.8V(OLED_Display).
And, I wondering about TXS & TXB.
I think TXB is best for my schematics, because TXS is designed for SPI, Is that right?
Recommand right part for my schematics.
Best regards,
Inho Jeon.
Hi Inho,
Thanks for the additional information.
Down translation is actually very easy and opens up the number of parts available to achieve it.
So, to achieve your desired startup reset of the OLED_RST, I would recommend eliminating the RC circuit and using the SN74LVC1G34. Here's a schematic of my idea:
The buffer is the SN74LVC1G34. The inputs can be driven at 3.2V while the device is powered from 1.8V. Note the 10kohm pull-down resistor. This will ensure that the reset is held LOW until the MCU is powered on and can control the RST\ pin itself.
For the other pins, I would recommend using the SN74AVC4T774. This device allows for individual channels to be going different directions (A to B or B to A) but all channels are buffered and unidirectional, which I believe is what you need here.
Together, the SN74LVC1G34 (0.8 x 0.8 mm) and the SN74AVC4T774 (2.6 x 1.8 mm) won't take up much space in your wearable device
Hi Inho,
You mean TXS & TXB are right for my schematics, Is that right?
No, I never said that, nor do I mean it.
From the schematic, it looks like you are connecting the translator to some kind of connector - I'm not sure of the capacitive load there, but a unidirectional solution will be far more likely to work in that situation. TXS or TXB might function, but they are definitely not the optimal solution here.
AVC4T774 isn't the only solution - it's just kind of a 'catch all' that will definitely work for your system. Unidirectional buffers are some of the smallest and lowest cost components available... so I'm not sure what you mean by 'issue of size & cost'
You mean your recommaned parts(SN74XXXXXXXX) is replaced to RC delay circuit, Is that right?
I think for issue of size & cost, I'll do not apply your recommanded parts for OLED_RST/.
Yes, that's what I mean.
It's fine if you don't use my design, but I don't think you understand why I suggested it.
You are connecting an RC circuit directly to a CMOS input. That will cause internal oscillation and shoot-through current during every power cycle, and will significantly reduce the lifetime of your semiconductor devices. You might want to read this application report: Implications of Slow or Floating CMOS Inputs
If many of these devices fail once customers get them, how much will it end up costing the company when a few cents could have entirely avoided the issue?
Hi Emrys,
Thank you for your reply.
I mean 'issue of size & cost' is just for working samples. I know about your meant.
But it is no time to show my working Spls for end-customer.
In pre-prodution, I apply to your comments for my products.
And, I have a question.
On my schematics, for level shifting of line 5 ports ; 4 ports of SPI & 1 port of RESET.
I saw your application resport on Ti web page below this ;
"The TXB push-pull buffered type architecture uses autodirection sensing to remove the requirement for a
DIR control signal to establish the direction of data flow. This architecture is designed to exclusively be
connected and interfaced with a push-pull CMOS driver and is capable of driving capacitive or high
impedance loads in applications such as Secure Digital (SD) or Serial Peripheral Interface (SPI).
The TXS translators also use autodirection sensing and offer system designers a good solution to remedy
mixed-voltage system incompatibilities when interfacing with open-drain drivers in applications such as
I2C."
So, I think 'TXB0108' is right to 5 ports of level shift on my schematics, Is that right?
Please, Inform me that question, ASAP.
Best Regards,
Inho Jeon