MP4569 - I_peak?

DC-DC Power Converters
#1

MP4569 design

I’m looking for a definition of “Ipeak” mentioned in the datasheet and formulas. It is stated that it is fixed, but I cannot find any specification nor how to calculate it. Please advise.

I’m planning to use the part as a bias-generator for a Forward, active clamp controller. Thus the expected current draw is in the range of 5-30 mA.

Will this part stay stable at extremely low Iout-currents and using a very high inductor value?

  • e.g. 100uH-220uH (Vin range = 28-60V)(Vout=10V)

Looking forward to hearing from you :smiley:

#2

Looks like it is the peak current the upper NMOS turns off at. Looks like this part works as a “gated oscillator” If Vout is under the setpoint, then the upper FET is turned on until Ipeak is reached and then turned off until the inductor current falls to zero. This cycle is repeated until Vout is above the setpoint at which point the thing doesn’t switch.

You can see pictures of light load operation where the inductor current still goes up to well over 500mA ( but not very often)

You need an inductor that has Isat of 800mA or higher

Ipeak is fixed internally you can’t adjust it. nor calculate it. It is set in the block diagram by the Ilimit comparator that (sets the flip flop) that turns off the upper fet and turns on the lower fet. That flip flop then flips or flops next turning on the upper fet and turning off the lower fet when the feedback voltage is too lower AND the zero current condition has been detected.

#3

Jshannon,
Thanks for diverting my thoughts in the right direction :slight_smile:

Yes, this coincides with my understanding as well. A sort of one-shot triggered by slightly too low voltage on the output turns on the high-side switch and don’t turn off until the current has reached I_limit.
After reviewing the ELECTRICAL CHARACTERISTICS page again for MP4569, I find the “Peak Current Limit” provided as Typ 730mA (min 670/max790 mA) which I believe must be the “I_limit” mentioned ion the formulas.

Best regards
Grizzly

#4

It also corresponds the maximum output current. At full load the inductor current will be a triangle between Ilim ( could be as low as 670) and zero the average value of that would be 335mA call it 300 for some dead times or gate delays.