FAN5018BMTCX Fairchild Semiconductor, FAN5018BMTCX Datasheet - Page 26

• Manufacturer Part Number: FAN5018BMTCX
• Description: IC CTRLR DC-DC MULTIPH 28TSSOP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN5018BMTCX

• Applications: Controller, High-Current, Implementing Low-Voltage CPU Core Power Circuits
• Voltage - Input: 12V
• Number Of Outputs: 1
• Voltage - Output: 0.5 ~ 3.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FAN5018B
10. Measure the output ripple at no-load and full-load with a
AC Loadline Setting
11. Remove DC load from circuit and hook up dynamic
12. Hook up scope to output voltage and set to DC coupling
13. Set dynamic load for a transient step of approximately
14. Measure the output waveform (may have to use DC off-
15. You will see a waveform that looks something like
NOTE: DO NOT MEASURE THE UNDERSHOOT OR
OVERSHOOT THAT HAPPENS IMMEDIATELY AFTER
THE STEP.
16. If the V
17. Repeat Steps 11 to 13 and repeat adjustments if
26
R
CS
(
scope and make sure it is within spec.
load.
with a time scale at 100µs/div.
40A at 1kHz with 50% duty cycle.
set on scope to see waveform). Try to use a vertical
scale of 100 mV/div or finer.
Figure 8. Use the horizontal cursors to measure V
and V
couple of millivolts, use Equation 38 to adjust C
may need to parallel different values to get the right one
since there are limited standard capacitor values avail-
able (it is a good idea to have locations for two capaci-
tors in the layout for this).
necessary. Once complete, do not change C
rest of the procedure.
NEW
C
CS
100
80
60
40
20
)
0
(
=
NEW
0
DCDRP
R
ACDRP
)
CS
Figure 8. AC Loadline Waveform
=
( 1
C
OLD
10
CS
as shown.
)
and V
(
×
OLD
R
TH
)
OUTPUT CURRENT (A)
×
(
20
DCDRP
25
V
V
o
DCDRP
ACDRP
C
)
+
(
R
30
are different by more than a
R
CS
CS
( 2
(
OLD
OLD
)
40
)
−
+
R
R
CS
TH
( 2
(
1
25
NEW
50
CS
o
C
)
)
for the
)
(38)
×
CS
ACDRP
(
R
60
. You
CS
( 1
OLD
)
−
R
18. Set the dynamic load step to the maximum step size (do
Initial Transient Setting
19. With dynamic load still set at maximum step size,
20. If both overshoots are larger than desired, try making
21. For load release (see Figure 10), if V
TH
(
25
not use a step size larger than needed) and verify that the
output waveform is square (which means VACDRP and
VDCDRP are equal). NOTE: MAKE SURE LOAD
STEP SLEW RATE AND TURN-ON ARE SET FOR A
SLEW RATE OF ~150–250A/µs (for example, a load
step of 50A should take 200ns–300ns) WITH NO
OVERSHOOT. Some dynamic loads will have an
excessive turn-on overshoot if a minimum current is not
set properly (this is an issue if using a VTT tool).
expand the scope time scale to see 2µs/div to 5µs/div.
You will see a waveform that may have two overshoots
and one minor undershoot (see Figure 9). Here, V
is the final desired value.
the following adjustments in this order. (NOTE: If these
adjustments do not change the response, you are limited
by the output decoupling.) Check the output response
each time you make a change as well as the switching
nodes (to make sure it is still stable).
a. Make ramp resistor larger by 25% (R
b. For V
c. For V
than V
output capacitance. You will either need more capaci-
tance or need to make the inductor values smaller (if
you change inductors, you need to start the design over
using the spreadsheet and this tuning procedure).
o
C
)
)
quency.
−
Figure 9. Transient Setting Waveform
R
TRAN1
TH
1
TRAN1
TRAN2
(
25
o
C
)
(see Figure 9), you do not have enough
, increase CB or increase switching fre-
, increase R
(37)
A
and decrease C
PRODUCT SPECIFICATION
REV. 1.0.0 Jul/15/05
TRANREL
RAMP
A
).
is larger
by 25%.
DROOP