FAN5018BMTCX Fairchild Semiconductor, FAN5018BMTCX Datasheet - Page 27

• 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

PRODUCT SPECIFICATION
Since the FAN5018B turns off all of the phases (switches
inductors to ground), there is no ripple voltage present
during load release. Thus, you do not have to add headroom
for ripple, allowing your load release V
than V
V
this implies that capacitors can be removed. When removing
capacitors, check the output ripple voltage as well to ensure
it is still within spec.
Layout and Component Placement
The following guidelines are recommended for optimal
performance of a switching regulator in a PC system.
Key layout issues are illustrated in Figure 11.
REV. 1.0.0 Jul/15/05
TRAN1
TRAN1
and V
Figure 10. Transient Setting Waveform
Figure 11. Layout Recommendations
by that amount and still be meeting spec. If
TRANREL
are less than the desired final droop,
TRANREL
to be larger
General Recommendations
• For good results, at least a four-layer PCB is
• Whenever high currents must be routed between PCB
• If critical signal lines (including the output voltage sense
• Use an analog ground plane both around and under the
• Connect the components around the FAN5018B close to
• Connect the output capacitors as close as possible to the
Power Circuitry
• Route the switching power path on the PCB to encompass
recommended. This should allow the needed versatility
for control circuitry interconnections with optimal
placement, power planes for ground, input, and output
power, and wide interconnection traces in the rest of the
power delivery current paths. Keep in mind that each
square unit of 1 ounce copper trace has a resistance of
~0.53 m
layers, vias should be used liberally to create several
parallel current paths so that the resistance and inductance
introduced by these current paths is minimized and the via
current rating is not exceeded.
lines of the FAN5018B) must cross through power
circuitry, it is best if a signal ground plane can be
interposed between those signal lines and the traces of the
power circuitry to serves as a shield to minimize noise
injection into the signals..
FAN5018B for ground connections to the components
associated with the controller. Tie this plane to the nearest
output decoupling capacitor ground and not to any other
power circuitry to prevent power currents from flowing in
it.
the controller with short traces. The most important traces
to keep short and away from other traces are the FB and
CSSUM pins.
load (or connector) that receives the power (e.g., a
microprocessor core). If the load is distributed, the
capacitors should also be distributed, and generally in
proportion to where the load tends to be more dynamic.
the shortest possible length in order to minimize radiated
switching noise energy (i.e., EMI) and conduction losses
in the board. Failure to take proper precautions often
results in EMI problems for the entire PC system as well
as noise related operational problems in the power
converter control circuitry. The switching power path is
the loop formed by the current path through the input
capacitors and the power MOSFETs including all
interconnecting PCB traces and planes. The use of short
and wide interconnection traces is especially critical in
this path for two reasons: it minimizes the inductance in
the switching loop, which can cause high-energy ringing,
and it accommodates the high current demand with
minimal voltage loss. Avoid crossing any signal lines over
the switching power path loop, described below.
Ω
at room temperature.
FAN5018B
27