FAN53168MTC FAIRCHILD [Fairchild Semiconductor], FAN53168MTC Datasheet - Page 24

• Manufacturer Part Number: FAN53168MTC
• Description: 6-Bit VID Controlled 2-4 Phase DC-DC Controller
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

FAN53168
16. If the V
17. Repeat Steps 11 to 13 and repeat adjustments if neces-
18. Set dynamic load step to maximum step size (do not use
Initial Transient Setting
19. With dynamic load still set at maximum step size,
24
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).
sary. Once complete, do not change C
the procedure.
a step size larger than needed) and verify that the output
waveform is square (which means V
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 200 ns–300 ns) 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 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
the final desired value.
C
CS NEW
(
ACDRP
Figure 8. AC Loadline Waveform
)
=
C
and V
CS OLD
(
DCDRP
)
×
V
--------------------- -
V
ACDRP
DCDRP
are different by more than a
ACDRP and
CS
for the rest of
DROOP
V
CS
DCDRP
. You
(38)
is
20. If both overshoots are larger than desired, try making the
21. For load release (see Figure 10), if V
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).
than V
output capacitance. You will either need more capaci-
tance or to make the inductor values smaller (if you
change inductors, you need to start the design over using
the spreadsheet and this tuning procedure).
a. Make ramp resistor larger by 25% (R
b. For V
c. For V
frequency.
Figure 10. Transient Setting Waveform
Figure 9. Transient Setting Waveform
TRAN1
TRAN1
TRAN2
(see Figure 9), you do not have enough
, increase C
, increase R
B
A
or increase switching
and decrease C
PRODUCT SPECIFICATION
TRANREL
REV. 1.0.0 6/9/03
RAMP
A
).
is larger
by 25%.