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TPS53625 Vcs(ocp) Setting Problem

user5324547
Prodigy 60 points
Other Parts Discussed in Thread: TPS53625

Hi

Recently I used TPS53625 as my x86(ATOM C3000) CPU VR chip. I set the TPS53625 min Vcs(ocp) value to 4.5mV. When I run linux on the CPU.I found the running speed is very slow. I use dd command the write sata disk for testing the performance of the CPU, write 1GB file,  the speed is 22MB/s。 Then I found when I set the Vcs(ocp) value to 36.7mV. The performance of CPU increased obviously. The same sata disk write test for 112MB/s speed.  I am confused. why the Vcs(ocp) setting can make such big influence on CPU performance?  the TPS53625 Icc(max) setting is above the CPU demand current.

  • 0
    TI__Prodigy 270 points
    If you did change the top resistor when you change OCP value, then the limitation could be due to limited current capability from VR to CPU. If the current is limited, CPU voltage could drop when it tried to pull more currents, and that could degrade CPU performance. OCP setting should be set according the selected inductor and power FET current rating, and should be able to provide current higher than imax.
  • 0 in reply to Brian (CPM-USA) Cheng
    Prodigy 60 points
    Hi，
    When the Vcs(ocp) is 4.5mV . In linux I see the cpu state and working freq in /sys/devices/system/cpu/cpu0/cpufreq/. I found the CPU state is in ondemand and the freq will raise to its max when I run some test software like dd on cpu. The situlation as Vcs(ocp)36.7mV is the same. I used to thought that the cpu running freq (in Vcs(ocp)4.5mV ) should be slower than cpu running freq (in Vcs(ocp)36.7mV), so the dd test resulted as memtioned above. But From /sys/devices/system/cpu/cpu0/cpufreq/, the two situlation seems no difference on cpu running freq behavior.
    You said the CPU vlotage drop would degrade cpu performance. I still can't totally understand how. VR vlotage is a range, not fixed.
  • 0 in reply to user5324547
    TI__Intellectual 1790 points

    Hi,

    when part hits over current limit, then output voltage to start drop.so system will shutdown. if you increase current limit, then output voltage will not drop.

    Thanks.

    Regards,

    Rama.