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UCD9244 Power Good and Bank 2

Maxim Galkin
Intellectual 460 points
Other Parts Discussed in Thread: UCD9244, UCD7242, UCD9222, UCD9224

Hello!

We use two UCD9244 + 2 x UCD7242 in our project for Zync7000 FPGA supply.

We have two problems:

1. How to program UCD9244 Power Good pin #24 by means of Fusion Digital Power Design? Power Good line pull-ups to Vdd (3,3V) in our desing by 10kOhm resistor. Power Good is set low when UCD9244 overheat. Power Good is set to Hi-Z when all power rails is ok. May I change Power Good pin Hi-Z state to only High state? How can I do it?

2. We use Fusion Digital Power Design (version 2.0.120) for UCD9244 configuration. I read in UCD9244 datasheet (page 21): Additionally, the UCD9244 has three banks of filter coefficients: Bank-0 is used during the soft start/stop ramp or tracking; Bank-1 is used while in regulation mode; and Bank-2 is used when the measured output current is below the configured light load threshold. How I can program bank 2? Why bank 2 tab is absent in Fusion Digital Power Design?

  • 0
    TI__Genius 13700 points

    The reference to Bank 2 in the UCD9244 datasheet is an artifact left over from the original UCD controller datasheets (ex. UCD9224) which were capable of implementing multi-phase rails.  The UCD9222 and the UCD9244 controllers were designed to implement only single phase rails and thus do not require the Bank 2 compensation parameters.  Please disregard the Bank 2 reference.

    Bank 2 can only be used on a controller with a multiphase rail which implements phase shedding.  As the output load current drops below a configurable level, a multi-phase rail controller with phase shedding enabled can disable one or more phases to reduce the overall switching losses of the converter.  Bank 2 is used to compensate the rail during this phase shedding condition.

  • 0 in reply to Brad
    Intellectual 460 points
    Brad, thanks for reply about bank 2.
    I hoped that we can compensate power loss on light load by means of bank 2 configuration. Current consumption of our board is about 540 mA (Vin = 7,5 V) and 500 mA (Vin = 12 V) at light load (10kOhm load on all power rails). We added 10 Ohm resistor on 3,3 V bus and input current increased from 540 mA to 690 mA (Vin = 7,5V, Theoretical current increase with efficiency 0,95: 540mA + 3,3V/10Ohm*(3,3V/7,5V)/0,95 = 692 mA). We added another resistor (4,7 Ohm) on other power rails. Experimental results is fully equal to theoretical calculations. I cann't understand why current consumption is so significant at light load? Power supply of both UCD9244's is made on two LDO LM1117-3.3. Why input current is slighlty proportional to input voltage? Moreover, our power supply on 2xUCD9244 is overheating after 10 minutes work when Vin = 12.
    Best regards, Maxim Galkin.
  • 0 in reply to Brad
    Intellectual 460 points
    Hi, Brad
    May you help us with Power Good pin use and light load efficiency increase?
    Best regards, Maxim Galkin.