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ADP3207 Datasheet(PDF) 26 Page - ON Semiconductor

Part No. ADP3207
Description  CPU Synchronous Buck Controller
Download  29 Pages
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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ADP3207 Datasheet(HTML) 26 Page - ON Semiconductor

 
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ADP3207
Rev. 1 | Page 26 of 29 | www.onsemi.com
2.
Hook-up the dc load to the circuit. Turn the circuit on and
verify operation. Check for jitter at no load and full load.
DC Loadline Setting
3.
Measure the output voltage at no load (VNL). Verify that it
is within tolerance.
4.
Measure the output voltage at full load and at cold (VFLCOLD).
Let the board set for a ~10 minutes at full load and measure
the output (VFLHOT). If there is a change of more than a few
millivolts, then adjust RCS1 and RCS2 using Equation 40 and
Equation 41.
FLHOT
NL
FLCOLD
NL
OLD
CS
NEW
CS
V
V
V
V
R
R
×
=
)
(
2
)
(
2
(40)
5.
Repeat Step 4 until cold and hot voltage measurements
remain the same.
6.
Measure output voltage from no load to full load using 5 A
steps. Compute the load line slope for each change and
then average it to get the overall load line slope (ROMEAS).
7.
If ROMEAS is off from RO by more than 0.05 m
Ω, use the
following to adjust the RPH values:
O
OMEAS
OLD
PH
NEW
PH
R
R
R
R
×
=
)
(
)
(
(41)
8.
Repeat Step 6 and Step 7 to check load line and repeat
adjustments if necessary.
9.
Once complete with dc load line adjustment, do not change
RPH, RCS1, RCS2, or RTH for the rest of procedure.
10. Measure output ripple at no load and full load with a scope
to make sure it is within specification.
AC Loadline Setting
VACDRP
VDCDRP
Figure 14. 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 15. 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
CS
NEW
CS
V
V
C
C
×
=
)
(
)
(
(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 15). Here, VDROOP is the final desired value.
VDROOP
VTRAN1
VTRAN2
Figure 15. Transient Setting Waveform, Load Step


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