Other Parts Discussed in Thread: TMS320F2812, , TPS7A87, LM3880, SN74CBTD3384
Hi,I have a design use TMS320F2812 and use TPS75005 for power,it provides 3.3V and 1.9V.But when i read the manual of TPS75005 i found a problem.When TPS75005 match 2812,the pin SEQ will connect to a hign leval and i do it.In the manual,the power up sequence is like that:
As you see,when SEQ is H,the sequence is EN、3.3V、1.9V,when the 3.3 and 1.9 is ok,PG will be H.But my design was not like this,this is my logic:
But when i use both 1nF capacitance to CT1 CT2 SS1 SS2，the requence i got by oscilloscope is like that:
The PG if faster than 3V3 and 1V9,PG connects to XRS.At this way i dont know It doesn't matter to 2812？？？Does it works normal?????
And if i use 10nF to CT1 and CT2,the requense is OK ,like that:
It looks right,but the speed of the 3V3 and 1V9 power start is lower than normal,is it right?
Now i want to know what"s wrong with this chip,and how can i do to solve this problem????Use 10nF?or change the logic??Or how can i select the cap to achieve the desired effect??Thanks very much!!!!!!!!!
