ADP3210 Datasheet, PDF (33/38 Pages) ON Semiconductor – 7-Bit Programmable Multiphase Mobile CPU Synchronous

AC Loadline Setting
V_ACDRP
V_DCDRP
ADP3210
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.
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 V_ACDRP
and V_DCDRP as shown. Do not measure the undershoot or
overshoot that occurs immediately after the step.
16. If the V_ACDRP and V_DCDRP are different by more than a couple
of mV, use the following to adjust C_CS (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):
C_{CS(NEW )}
= C_CS(OLD)
×
V_ACDRP
V_DCDRP
(42)
17. Repeat Steps15 and Step 16. Repeat adjustments if
necessary. Once complete, do not change C_CS 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 V_ACDRP and V_DCDRP 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
V_DROOP
V_TRAN1
V_TRAN2
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.
a. Make ramp resistor larger by 25% (R_RAMP).
b. For V_TRAN1, increase C_B or increase switching
frequency.
c. For V_TRAN2, increase R_A and decrease C_A both by 25%.
21. For load release (see Figure 30), if V_TRANREL 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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