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Powering the C5535 : Same 3v3 supply rail for DVDDIO and LDOI

Nicolas Deup
Intellectual 590 points
Hi, I have been able to access all information from the very very interesting link processors.wiki.ti.com/.../35_Schematic_Checklist and {{#tiwikiurl:C5000_DSP_based_Low-power_system_design | C5000 DSP based Low-power system design}} {{#tiwikiurl:Optimizing_IO_Power_Consumption | Optimizing_IO_Power_Consumption}} I am trying on my project to reduce the number of LDOs. Up to now, I need 3 : 1v3 for RTC 1v8 for LDOin 3v3 for DVDDIO I guess that only one 3v3 LDO should be enough, since LDOI can be supply at 3v3, and I can get the 1v3 with a cheap resistor divider (10KOhm PU, 6.5KOhm PD) as explain is the aboce links. My question is the following : is there any reason why a lot of C5535 project (Boost pack, some ref design, ...) have one LDO for the 1v8 and one LDO for the 3v3 ? What are really the LDO requirements to power the C5535 is I only use one ? Is 100mA enough ? Fast transient ? Low noise ? What may be the cheapest solution to provide the 1v3 ? In fact, a resistor divider (3v3 10kOhm PU+ 6.5kPD ) to get 1v3 for the RTC will always sink 200uA, which is too much for my application. Thanks a lot for your comments. Nicolas the LDOI input is always 1v8 and DVDDIO is 3v3 ? I really do not see any reason to have 1 LDO to provide
  • 0
    TI__Mastermind 23785 points
    LDOI is spec'ed as 1.8V to 3.6V. The 1.8V minimum is very restricted. DVDDIO can be 1.8V to 3.3V. As long as you can meet the spec requirements, there is no restriction on external LDO used.
    Regards.
  • 0 in reply to Steve Tsang
    Intellectual 590 points
    Steve, OK, I will so only use one LDO rather than 2. Note that I am in the typical 100 MHz application case. My concern is the peak an mean current that may provide the LDO. Even if the DSP total mean current is approx 30mA, when GPIO toggles (I guess 4mA per pin), peak current may reach much much higher value. Note that I am using the typical 100nF / 1uF decoupling cap values proposed in the datasheet. Any idea about the LDO 's specs ? Any idea about a LDO/ref part number the provide the 1v3 for the DvddRTC ? thanks.