Hello,
In our system we are using the TLV320AIC3254 audio codec. Currently we are having some strange problems with the power up sequence of our codec, where we are in the assumption that we are working according to the specification.
The codec power is wired as follows:
IOVDD: 1.8V
LDO_SELECT: IOVDD -> 1.8V
LDOIN: 3.0V
DVDD and AVDD are supplied by the internal LDO. These are connected as described in Design and Configuration guide, page 10, figure 4, scenario A (http://www.ti.com/litv/pdf/slaa404c).
We first power the IOVDD and 1 second later we power the LDOIN. At all times the RESET line is kept low. What we experience is that I2C communication is not functioning, because one or both of the I2C lines (SCL and SDA) are kept low and thus keeping the bus.
We tried to shorten the power up time between IOVDD and LDOIN to ~4 ms, where IOVDD was powered first again. This again often led to the exact same failure. According to the Power Supply Sequencing documentation (http://www.ti.com/litv/pdf/slaa492a) this should be a valid scenario, but for us it did not work.
The problem is resolved when we hardwire LDOIN to 3.0V, thus we can no longer turn it on and off, and then turn on the power the IOVDD pin about 1 second later. Thus first power the LDOIN pin and then powering the IOVDD pin. If we follow this scenario, the I2C bus errors do not show up. But this would be against the specification of the codec chip.
The problem also disappears if we power on IOVDD and LDOIN at the exact same time.
Hopefully someone can give us some kind of indication of what is going wrong here.
Thank you in advance for you help.
Kind regards,
Marcel