What is the purpose of this AND gate on the USB input?

[abdullahseba]

Hi
I'm designing a USB to audio as part of a bigger circuit. I choose the PCM2901 form ti http://www.ti.com/lit/ds/symlink/pcm2901.pdf . In the datasheet it shows an AND gate connected to the USB power and the 3.3V for the chip. So at first I thought it might be to power the ship on when both supplies where on. But then I saw that the output connected to the data+ of the USB. What is the purpose of this gate? is it to do with the USB specification? can I use 2 2N2222 instead of a complete logic chip?
Also I don't get the SSPND pin. Any clue to what that does?
Thanks in advance.

[newbrain]

A pull-up on D+ (or D- for low speed) is needed to signal the host that an USB device is connected, using an AND gate will make sure that will happen only when both Vbus and Vdd are there (but it is not shown where the AND should get its power...Vcc?).

For further details see here, in the "Speed Identification" section.

There should be no problem in driving the pull-up with a suitable BJT circuit.

[abdullahseba]

(but it is not shown where the AND should get its power...Vcc?)

Probably wont matter in my case as both come on at the same time from two regulators.

[newbrain]

If the device is bus powered (i.e. Vcc/Vdd derived from Vusb), you can just connect the 1.5KOhm pull up to Vcc/Vdd (when Vusb goes away, the pull up goes away).

If, instead it's self powered, you need to sense the Vusb, a transistor and some resistors will nicely do.

[Zero999]

Hi
I'm designing a USB to audio as part of a bigger circuit. I choose the PCM2901 form ti http://www.ti.com/lit/ds/symlink/pcm2901.pdf . In the datasheet it shows an AND gate connected to the USB power and the 3.3V for the chip. So at first I thought it might be to power the ship on when both supplies where on. But then I saw that the output connected to the data+ of the USB. What is the purpose of this gate? is it to do with the USB specification? can I use 2 2N2222 instead of a complete logic chip?
Also I don't get the SSPND pin. Any clue to what that does?
Thanks in advance.

You could use transistors but why would you want to? If you need to save space, then there are single and dual NAND/AND gate packages available.
http://www.ti.com/lit/ds/symlink/sn74lvc2g00.pdf
https://assets.nexperia.com/documents/data-sheet/74HC_HCT2G00.pdf
https://assets.nexperia.com/documents/data-sheet/74LVC1G08.pdf

[abdullahseba]

You could use transistors but why would you want to? If you need to save space, then there are single and dual NAND/AND gate packages available.

Thanks! Will do.