ADP3210 datasheet(33/38 Pages) ONSEMI

33 / 38 page

ADP3210

Rev. 0.3 | Page 33 of 38

AC Loadline Setting

VACDRP

VDCDRP

Figure 28. AC Loadline Waveform

11. Remove the dc load from the circuit and hook up the dynamic

load.

12. Hook up the scope to the output voltage and set it to dc

coupling with the time scale at 100 μs/div.

13. Set the dynamic load for a transient step of about 40 A at

1 kHz with a 50% duty cycle.

14. Measure the output waveform (using the dc offset on scope

to see the waveform, if necessary). Try to use the vertical

scale of 100 mV/div or finer.

15. Users should see a waveform that similar to the one in

Figure 29. Use the horizontal cursors to measure VACDRP

and VDCDRP as shown. Do not measure the undershoot or

overshoot that occurs immediately after the step.

16. If the VACDRP and VDCDRP are different by more than a couple

of mV, use the following to adjust CCS (note that users may

need to parallel different values to get the right one due to

the limited standard capacitor values available. It is also wise

to have locations for two capacitors in the layout for this):

DCDRP

ACDRP

OLD

NEW

)

(

)

(

(42)

17. Repeat Steps15 and Step 16. Repeat adjustments if

necessary. Once complete, do not change CCS for the

rest of the procedure.

18. Set dynamic load step to maximum step size. Do not use a

step size larger than needed. Verify that the output waveform

is square, which means VACDRP and VDCDRP are equal.

Note: Make sure that the load step slew rate and turn-on

are set for a slew rate of ~150 A/μs to 250 A/μs (for

example, a load step of 50 A should take 200 ns to 300 ns)

with no overshoot. Some dynamic loads have an excessive

turn-on overshoot if a minimum current is not set properly

(this is an issue if you are using a VTT tool).

Initial Transient Setting

19. With dynamic load still set at the maximum step size, expand

the scope time scale to see 2 μs/div to 5 μs/div. A waveform

that has two overshoots and one minor undershoot can result

(see Figure 29). Here, VDROOP is the final desired value.

VDROOP

VTRAN1

VTRAN2

Figure 29. Transient Setting Waveform, Load Step

20. If both overshoots are larger than desired, make the

following adjustments in the order they appear. Note that if

these adjustments do not change the response, then users

are limited by the output decoupling. In addition, check

the output response each time a change is made, as well as

the switching nodes to make sure they are still stable.

Make ramp resistor larger by 25% (RRAMP).

For VTRAN1, increase CB or increase switching

frequency.

For VTRAN2, increase RA and decrease CA both by 25%.

21. For load release (see Figure 30), if VTRANREL is larger than

the IMVP-6 specification, there is not enough output

capacitance. Either more capacitance is needed or the

inductor values needed to be smaller. If the inductors are

changed, then start the design over using Equation 1 to

Equation 39 and this tuning guide.

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