ADP3209 ON Semiconductor, ADP3209 Datasheet - Page 29

• Manufacturer Part Number: ADP3209
• Description: 5-bit, Programmable, Single-phase, Synchronous Buck Controller
• Manufacturer: ON Semiconductor

C
di/dt REDUCTION
In continuous inductor-current mode, the source current of the
high-side MOSFET is approximately a square wave with a duty
ratio equal to V
low ESR input capacitor sized for the maximum rms current.
The maximum rms capacitor current occurs at the lowest input
voltage and is given by
where I
In a typical notebook system, the battery rail decoupling is
achieved by using MLC capacitors or a mixture of MLC
capacitors and bulk capacitors. In this example, the input
capacitor bank is formed by four pieces of 10 μF, 25 V MLC
capacitors, with a ripple current rating of about 1.5 A each.
SOFT TRANSIENT SETTING
As described in the Theory of Operation section, during the soft
transient, the slew rate of the V
controlled by the ST pin capacitance. The ST pin capacitance is
set to satisfy the slew rate for a fast exit as follows:
where:
7.5 μA is the source/sink current of the ST pin.
SLEWRATE is the voltage slew rate after a change in VID voltage
and is defined as 10 mV/μA in the IMVP-6+ specification.
C
TUNING PROCEDURE FOR ADP3209
Set Up and Test the Circuit
1.
2.
3.
4.
Set the DC Load Line
1.
2.
ST
IN
is 750 pF, and the closest standard capacitance is 680 pF.
SELECTION AND INPUT CURRENT
Build a circuit based on the compensation values computed
from the design spreadsheet.
Connect a dc load to the circuit.
Turn on the ADP3209 and verify that it operates properly.
Check for jitter with no load and full load conditions.
Measure the output voltage with no load (V
that this voltage is within the specified tolerance range.
Measure the output voltage with a full load when the device is
cold (V
a full load and then measure the output when the device is
hot (V
C
I
I
CRMS
CRMS
ST
O
is the output current.
=
=
FLHOT
=
SLEWRATE
FLCOLD
. 0
D
7
15
OUT
×
5 .
). If the difference between the two measured
). Allow the board to run for ~10 minutes with
I
×
μA
/V
O
15
×
IN
A
. To prevent large voltage transients, use a
×
D
1
−
0.1
1
1
5
CCGFX
−
1
=
reference voltage change is
. 5
36
A
NL
) and verify
Rev. 2 | Page 29 of 32 | www.onsemi.com
(38)
(39)
3.
4.
5.
6.
7.
Set the AC Load Line
1.
2.
3.
4.
5.
6.
voltages is more than a few millivolts, adjust R
Equation 40.
Repeat Step 2 until no adjustment of R
Compare the output voltage with no load to that with a full
load using 5 A steps. Compute the load line slope for each
change and then find the average to determine the overall
load line slope (R
If the difference between R
use the following equation to adjust the R
Repeat Steps 4 and 5 until no adjustment of R
Once this is achieved, do not change R
for the rest of the procedure.
Measure the output ripple with no load and with a full load
with scope, making sure both are within the specifications.
Remove the dc load from the circuit and connect a
dynamic load.
Connect the scope to the output voltage and set it to dc
coupling mode with a time scale of 100 μs/div.
Set the dynamic load for a transient step of about 40 A at
1 kHz with 50% duty cycle.
Measure the output waveform (note that use of a dc offset
on the scope may be necessary to see the waveform). Try to
use a vertical scale of 100 mV/div or finer.
The resulting waveform will be similar to that shown in
Figure 38. 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 42 to adjust C
DCDRP
R
R
, as shown in Figure 38. Do not measure the under-
CS
PH
( 2
(
NEW
NEW
Figure 38. AC Load Line Waveform
)
)
=
=
R
R
OMEAS
PH
CS
( 2
(
OLD
OLD
).
)
)
OMEAS
×
×
ACDRP
R
V
V
OMEAS
NL
R
NL
and R
V
O
ACDRP
and V
−
−
V
V
FLCOLD
O
FLHOT
is more than 0.05 mΩ,
CS2
PH
DCDRP
, R
V
is needed.
PH
DCDRP
CS1
values:
is more than a
ADP3209
PH
, R
CS2
CS
is needed.
CS2
ACDRP
using
. It may
, or R
and
(40)
(41)
TH