Cyclone III FPGA power supply problem

[Altera_Forum]

hello, 

i am working on fpga based project. i m using cyclone3 fpga. in dat we hav 1.2v n 3.3v supplies necessary for i/o operation. we are using two TPS54310 ic's for both the supplies. we connected them on board according to the datasheet.but still we are not getting actual output. pin2 shud be 0.9v but we r getting 0.4v pin17 shud be 2.7v but we r getting 2.8v  across the inductor we shud get 3.3v, which is our output voltage but instead of that we are getting 1.8v only......  so can anyone suggest some testing methods or any alternatives to correct this problem..??  please suggest...its urgent because whole board connections depends on this 3.3v supply......  thank you ann

[Altera_Forum]

It's not actually a question related to Altera FPGA. Anyway... 

 TPS54310 doesn't exist. Do you mean TPS54311?    --- Quote Start ---  pin17 shud be 2.7v but we r getting 2.8v  --- Quote End ---   Read the datasheet once again.   --- Quote Start ---  pin2 shud be 0.9v but we r getting 0.4v  --- Quote End ---   You either overload the 3.3V node or your circuit is wrong somehow. Did you try to disconnect the load? You should show a complete schematic.

[Altera_Forum]

hello sir, 

i m workin on cyclone III altera FPGA chip..... TPS54310 does exist...it is Texas instruments IC. i have its datasheet. it is a SYNCHRONOUS BUCK PWM Regulator....3v to 6v input voltage. its output range is 1.2v to 3.3v.  (Acc. to Datasheet) 1) pin17 is VBIAS its voltage range is min 2.7v max 2.9v typical- 2.8v which is coming correctly  2) pin2 is VSENSE its voltage range is -0.3v to 4v which is coming around 0.4v but it should be 0.9v atleast for the IC to produce 3.3v.  the capacitor(6.8uF) we are using across the inductor(2.2H) at the output.  we tried without that capacitor......but its not showing any output.....  Vout is 0v.  sir i hope u got some idea abt the Ic we are using & the results we got....  plz suggest any ways or any other alternatives which we should use to correct this issue...  thank you ann

[Altera_Forum]

You are right about TPS54310, for some reason i didn't find it. But it's basically identical to the TPS54311 I mentioned. 

     --- Quote Start ---  the capacitor(6.8uF) we are using across the inductor(2.2H) at the output.  --- Quote End ---   Your additional explanations don't make much sense. No switch mode regulator uses an inductor of 2.2h. Do you mean µh? I also can't see, how a capacitor will be connected across the inductor.    --- Quote Start ---  pin2 is VSENSE its voltage range is -0.3v to 4v which is coming around 0.4v  --- Quote End ---    Do you mean, there is no stable measurement at all?    --- Quote Start ---  Vout is 0v.  --- Quote End ---   In this case, Vsense would be 0V as well, presuming a correct circuit and correctly performed measurement.   Two questions from my previous post are unanswered yet.   --- Quote Start ---  Did you try to disconnect the load? You should show a complete schematic.  --- Quote End ---  

[Altera_Forum]

sir, 

 i m sorry i wrote 2.2H by mistake. it is actually 22uH.  and the inductor & capacitor are connected parallel jus lyk it is in the TPS54310 ic datasheet...  so if we remove that capacitor, still the output is 0.  yes u r rite Vsense is 0 that time. but when we are using this capacitor, Vsense is around 0.4v instead of 0.9v.  i can't giv u the schematic...... i m not permitted to do so.....  i tried dis power supply circuit on an extra board,only present on the board, without even the main FBGA chip. still it is showing the same values...  i hope u got my problem now correctly.........  ann

[Altera_Forum]

--- Quote Start ---  the inductor & capacitor are connected parallel jus lyk it is in the TPS54310 ic datasheet..  --- Quote End ---   Referring to figure 10. tps54310 schematic, I don't see a capacitor parallel to the inductor. If you mean the output capcitor C9, a value of 6.8 µF would be rather small.    --- Quote Start ---  i tried dis power supply circuit on an extra board,only present on the board, without even the main FBGA chip. still it is showing the same values...  --- Quote End ---   I just can tell, that the TI switchers are basically working well. But TPS54310 has enough options to mess up the circuit somehow, in design and assembly as well.  You can try with a TPS54310 Evalboard.