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Voltage Level Translation Forum
TXS0104E: OK to power down VCCB?
I have a design using TXS0104E with VCCA=1.8V, VCCB=5V. All signals are inputs to the VCCA side.
I would like to power down the VCCB domain during operation to save power. The datasheet states:
"During operation, ensure that VCCA ≤ VCCB at all times. During power-up sequencing, VCCA ≥ VCCB does notdamage the device, so any power supply can be ramped up first."
So is it OK to power down VCCB? It sounds like I will not damage the device, but could this cause other problems?
Will power bleed through to the VCCB domain if the VCCA signals are driven high?
Here is the feedback for your questions. any unclear, pelase let me know.
[Q]So is it OK to power down VCCB? It sounds like I will not damage the device, but could this cause other problems?
[Junjie] Yes, it is OK. The TXS0104E has the Vcc isolation feature, whic means if you power down VccB while VccA is on, it will put the A side pins are in high-impedance state. it is Ok and will not cause the other problems.
But the TXS0104E doesn't have the Ioff feature, if you power down VccB, and drive high to B side, it will cause the high current to VccB. but since your application only have the input at A side, it will not have this issue.
[Q]Will power bleed through to the VCCB domain if the VCCA signals are driven high?
[Junjie] No, there is no path from A input side to VccB when VccB is down.
I noticed that on the latest versions of both the TXS0104e and TXS0108e datasheets that the VCC isolation feature is no longer mentioned on the first page. Comparing the datasheets for the TXS0108e, SCES642 (Dec 2007) mentions VCC isolation on the first sheet but this was removed in SCES642B (Sept 2008). Was there a problem with this feature and thus the datasheet was revised?
In my application, the VCCA side (1.8V) may be powered down while the VCCB side (3.3V) stays energized. I'm wondering if I can use this device to isolate the two power supply domains.
Thanks for your reminder for this, I will check the reason of this change. any update, will let you know.
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