13
magnitude of voltage spikes. See the Application Note
AN9915 for the evaluation board component placement and
the printed circuit board layout details.
There are two sets of critical components in a DC-DC
converter using an IPM6220A controller. The switching
power components are the most critical because they switch
large amounts of energy, and as such, they tend to generate
equally large amounts of noise. The critical small signal
components are those connected to sensitive nodes or
those supplying critical bias currents.
Power Components Layout Considerations
The power components and the controller IC should be
placed first. Locate the input capacitors, especially the high-
frequency ceramic decoupling capacitors, close to the power
MOSFETs. Locate the output inductor and output capacitors
between the MOSFETs and the load. Locate the PWM
controller close to the MOSFETs.
Insure the current paths from the input capacitors to the
MOSFETs, to the output inductors and output capacitors are
as short as possible with maximum allowable trace widths.
A multi-layer printed circuit board is recommended. Dedicate
one solid layer for a ground plane and make all critical
component ground connections with vias to this layer.
Dedicate another solid layer as a power plane and break this
plane into smaller islands of common voltage levels. The
power plane should support the input power and output power
nodes. Use copper filled polygons on the top and bottom
circuit layers for the phase nodes, but do not unnecessarily
oversize these particular islands. Since the phase nodes are
subjected to very high dV/dt voltages, the stray capacitor
formed between these islands and the surrounding circuitry
will tend to couple switching noise. Use the remaining printed
circuit layers for small signal wiring. The wiring traces from the
control IC to the MOSFET gate and source should be sized to
carry 2A peak currents.
Small Components Signal Layout Considerations
4. The VSNS1 and VSNS2 inputs should be bypassed with
a 1.0F capacitor close to their respective IC pins.
5. A ‘T’ filter consisting of a ‘split’ RSNS and a small, 100pF,
capacitor as shown in Figure 10, may be helpful in
reducing noise coupling into the ISEN input. For example,
if the calculated value of RSNS1 is 2.2k, dividing it as
shown with a 100pF capacitor provides filtering without
changing the current limit set point. For any calculated
value of RSNS, keep the value of the R9 portion to
approximately 200, and the remainder of the resistance
in the R19 position. The 200 resistor and 100pF
capacitor provide effective filtering for noise above 8MHz.
This filter configuration may be helpful on both the 3.3V and
5V Main outputs.
6. The bypass capacitors for VBATT and the soft-start
capacitors, C
SS1
and C
SS2
should be located close to
their connecting pins on the control IC. Minimize any
leakage current paths from SDWN1 and SDWN2 nodes,
since the internal current source is only 5A.
7. Refer to the Application Note AN9915 for a
recommended component placement and
interconnections.
Figure 11 shows an application circuit of a power supply for a
notebook PC microprocessor system. The power supply
provides +5V ALWAYS, +3.3V ALWAYS, +5.0V, +3.3V, and
12V from +5.6-22V
DC
battery voltage. For detailed information
on the circuit, including a Bill of Materials and circuit board
description, see Application Note AN9915. Also see Intersil’s
web site (www.intersil.com) for the latest information.
ISEN1
R19
R9
200
2K
C12
100pF
FROM PHASE
NODE
RSNS = R19 + R9
FIGURE 10. NOISE FILTER FOR ISEN1 INPUT
IPM6220A
