ADP3208C ON Semiconductor, ADP3208C Datasheet - Page 39

• Manufacturer Part Number: ADP3208C
• Description: 7-bit,programmable,dual- Phase,mobile,cpu,synchronous Buck Controller
• Manufacturer: ON Semiconductor

5.
6.
7.
8.
9.
Set the Initial Transient
1.
The resulting waveform will be similar to that shown in
Figure 41. Use the horizontal cursors to measure V
V
shoot or overshoot that occurs immediately after the step.
If the difference between V
couple of millivolts, use Equation 46 to adjust C
be necessary to try several parallel values to obtain an
adequate 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 reason).
Repeat Steps 5 and 6 until no adjustment of C
Once this is achieved, do not change C
procedure.
Set the dynamic load step to its maximum step size (but do
not use a step size that is larger than needed) and verify
that the output waveform is square, meaning V
V
Ensure that the load step slew rate and the power-up slew
rate are set to ~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
overshoot at power-up if a minimum current is incorrectly
set (this is an issue if a VTT tool is in use).
With the dynamic load set at its maximum step size,
expand the scope time scale to 2 μs/div to 5 μs/div. This
results in a waveform that may have two overshoots and
one minor undershoot before achieving the final desired
value after V
DCDRP
DCDRP
C
, as shown in Figure 41. Do not measure the under-
CS
are equal.
(
NEW
DROOP
Figure 41. AC Load Line Waveform
)
=
C
CS
(see Figure 42).
(
OLD
)
×
V
V
ACDRP
ACDRP
DCDRP
V
ACDRP
and V
DCDRP
CS
V
for the rest of the
DCDRP
is more than a
CS
ACDRP
Rev. 1 | Page 39 of 41 | www.onsemi.com
CS
is needed.
ACDRP
. It may
and
and
(37)
2.
3.
LAYOUT AND COMPONENT PLACEMENT
The following guidelines are recommended for optimal
performance of a switching regulator in a PC system.
If both overshoots are larger than desired, try the following
adjustments in the order shown.
a.
b.
c.
If these adjustments do not change the response, it is
because the system is limited by the output decoupling.
Check the output response and the switching nodes each
time a change is made to ensure that the output decoupling
is stable.
For load release (see Figure 43), if V
the value specified by IMVP-6+, a greater percentage of
output capacitance is needed. Either increase the
capacitance directly or decrease the inductor values. (If
inductors are changed, however, it will be necessary to
redesign the circuit using the information from the
spreadsheet and to repeat all tuning guide procedures).
Increase the resistance of the ramp resistor
(R
For V
frequency.
For V
Figure 43. Transient Setting Waveform, Load Release
Figure 42. Transient Setting Waveform, Load Step
RAMP
V
TRAN1
TRAN2
V
TRAN1
) by 25%.
TRANREL
, increase R
, increase C
V
TRAN2
A
B
by 25% and decrease C
or increase the switching
V
DROOP
V
DROOP
TRANREL
ADP3208C
is larger than
A
by 25%.