Looking for references for isolated line voltage measurements and zero crossing detection

Hello,

We have a client who would like us to provide their central microprocessor with either:

1. A scaled, isolated version of the line voltage in analog form ( a +/-3V signal, biased to1.65V DC for use with a 3.3VDC ADC on the secondary side)
   (or)
2. A pulsed signal which indicates when the utility voltage as crossed zero (must have known/quantifiable group delay)
   (or)
3. A digital replica of the line voltage from an isolated ADC

Main concern is that any group delay from the measurement of the line voltage from the replica is well defined, since the signal is used for timing.

The solution size needs to be as small as possible (30mm x 40mm maybe?) and offer the same isolation levels that our LLC transformer are specified to (>4000Vrms).

Before I dug into this, I thought that someone has likely already solved this problem and maybe I don't have to start from scratch. I wonder if TI might have a reference design or app note that I could reference?


Thanks in advance,
Cody