IRU3007
Start the layout by first placing the power components: 9) Place R12 and C10 close to pin 23 and R9 and C5
close to pin 9.
1) Place the input capacitors C3 and C14 and the high
side MOSFETs, Q1 and Q3 as close to their respec- 10) Place C9 close to pin 12
tive input caps as possible.
Component connections:
2) Place the synchronous MOSFET, Q2 and the Q3 as
close to each other as possible with the intention Note: It is extremely important that no data bus should
that the source of Q3 and drain of the Q4 has the be passing through the switching regulator section spe-
shortest length. Repeat this for the Q1 and D1 for the cifically close to the fast transition nodes such as PWM
non-synchronous.
drives or the inductor voltage.
3) Place the snubber R15 and C13 between Q4 and Q3. Using the 4 layer board, dedicate one layer to ground,
Repeat this for R1 and C4 with respect to the Q1 and another layer as the power layer for the 5V, 3.3V, Vcore,
D1 for the non-synchronous.
1.5V and if it is possible, for the 2.5V.
4) Place the output inductor , L3 and the output capaci- Connect all grounds to the ground plane using direct
tors, C16 between the MOSFET and the load with vias to the ground plane.
output capacitors distributed along the slot 1 and
close to it. Repeat this for L2 with respect to the C1 Use large low inductance/low impedance plane to con-
for the non-synchronous.
nect the following connections either using component
side or the solder side.
5) Place the bypass capacitors, C8 and C19 right next
to 12V and 5V pins. C8 next to the 12V, pin 28 and
C19 next to the 5V, pin 11.
a) C14 to Q3 Drain and C3 to Q1 drain
b) Q3 Source to Q4 Drain and Q1 Source to D1
cathode
6) Place the IRU3007 such that the pwm output drives,
pins 27 and 25 are relatively short distance from gates
of Q3 and Q4. The non-synch MOSFET must also
be situated such that the distance from its gate to
the pin 1 of the IRU3007 is also relatively short.
c) Q4 drain to L3 and D1 cathode to L2
d) L3 to the output capacitors, C16 and L2 to the
output capacitors, C1
e) C16 to the load, slot 1
f) Input filter L1 to the C16 and C3
g) C1 to Q2 drain
7) Place all resistor dividers close to their respective
feedback pins.
h) C17 to the Q2 source
I) A minimum of 0.2 inch width trace from the C18
capacitor to pin 16
8) Place the 2.5V output capacitor, C18 close to the pin
16 of the IC and the 1.5V output capacitor, C17 close Connect the rest of the components using the shortest
to the Q2 MOSFET.
connection possible.
Note: It is better to place the 1.5V linear regulator
components close to the IRU3007 and then run a
trace from the output of the regulator to the load.
However, if this is not possible then the trace from
the linear drive output pin, pin 18 must be run away
from any high frequency data signals.
It is critical, to place high frequency ceramic capaci-
tors close to the clock chip and termination resistors
to provide local bypassing.
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Data and specifications subject to change without notice. 02/01
Rev. 2.1
08/20/02
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15
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