Hi
We are implementing a power supply for the C6748 DSP based on LT's LTM4628 uModules and would like some clarification on the sequencing requirements of the 1.8 and 3.3 V supplies. In addition to a 1.2 V core voltage, our design uses both 1.8 (Groups B and C) and 3.3 V (Group A) IO voltages. The 1.2, 1.8 and 3.3 V supplies are also used to power the USB0 peripheral. (Dedicated USB1 and SATA peripheral supply pins are not connected.)
The datasheet states that the supplies should be sequenced 1.2, 1.8 then 3.3. Can you clarify whether this means that the 1.8 V supply must be fully up before the 3.3 V regulator is enabled or is it ok for the 1.8 and 3.3 V rails to ramp up to 1.8 V together, with the 3.3 V supply then continuing up to 3.3 V (ie, with the 1.8 V supply tracking the 3.3 V rail)? Alternatively could arrange 1.8 V rail to ramp at twice the rate of 3.3 V rail.
Thanks in advance
Tim