ADP3190
Rev. 2 | Page 22 of 27 | www.onsemi.com
9. Once dc load line adjustment is complete, do not change
R
PH
, R
CS1
, R
CS2
, or R
TH
for the remainder of the procedure.
10.
Measure the output ripple at no load and full load with a
scope, and make sure it is within specifications.
()
()
()
() ()
()
()
()
()
C)25(
C)25(
C)25(
C25
1
1
°
°
°
°
−
−
×−+×
+
=
TH
THOLDCS1
NEWCS2OLDCS1
TH
OLDCS1
THOLDCS1
NEWCS1
R
RR
RRRR
RR
R
(36)
AC Load Line Setting
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 (if not visible, use dc offset
on scope to view). Try to use a vertical scale of 100 mV/div
or finer. This waveform should look similar to Figure 14.
V
ACDRP
V
DCDRP
6529-015
Figure 14. AC Load Line Waveform
15. Use the horizontal cursors to measure V
ACDRP
and V
DCDRP
,
as shown. Do not measure the undershoot or overshoot
that happens immediately after this step.
If V
ACDRP
and V
DCDRP
are different by more than a few
millivolts, use Equation 38 to adjust C
CS.
It may be neces-
sary to parallel different values to get the correct one,
because there are limited standard capacitor values
available. It is a good idea to have locations for two
capacitors in the layout for this.
()
()
DCDRP
ACDRP
OLDCSNEWCS
V
CC ×= (38)
16.
Repeat Step 11 to Step 13, and repeat the adjustments, if
necessary. Once complete, do not change C
CS
for the
remainder of the procedure.
Set the dynamic load step to maximum step size. Do not
use a step size larger than needed, and verify that the output
waveform is square, which means that V
ACDRP
and V
DCDRP
are equal.
Initial Transient Setting
17. With the dynamic load still set at the maximum step size,
expand the scope time scale to see 2 µs/div to 5 µs/div. The
waveform may have two overshoots and one minor under-
shoot (see Figure 15). Here, V
DROOP
is the final desired value.
06529-016
V
DROOP
V
TRAN1
V
TRAN2
Figure 15. Transient Setting Waveform
18. If both overshoots are larger than desired, try making the
following adjustments:
•
Make the ramp resistor larger by 25% (R
RAMP
).
•
For V
TRAN1
, increase C
B
or increase the switching
frequency.
•
For V
TRAN2
, increase R
A
and decrease C
A
by 25%.
If these adjustments do not change the response, the output
decoupling is the limiting factor. Check the output response
every time a change is made, or nodes are switched, to
make sure the response remains stable.
19.
For load release (see Figure 16), if V
TRANREL
is larger than
V
TRAN1
(see Figure 15), there is not enough output capaci-
tance. Either more capacitance is needed or the inductor
values need to be smaller. If inductors are changed, start
the design again using the spreadsheet and this tuning
procedure.
