IRU3007

15

Rev. 2.1

08/20/02

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Start the layout by first placing the power components:

1) Place the input capacitors C3 and C14 and the high

side MOSFETs, Q1 and Q3 as close to their respec-

tive input caps as possible.

2) Place the synchronous MOSFET, Q2 and the Q3 as

close to each other as possible with the intention

that the source of Q3 and drain of the Q4 has the

shortest length. Repeat this for the Q1 and D1 for the

non-synchronous.

3) Place the snubber R15 and C13 between Q4 and Q3.

Repeat this for R1 and C4 with respect to the Q1 and

D1 for the non-synchronous.

4) Place the output inductor , L3 and the output capaci-

tors, C16 between the MOSFET and the load with

output capacitors distributed along the slot 1 and

close to it. Repeat this for L2 with respect to the C1

for the non-synchronous.

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.

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.

7) Place all resistor dividers close to their respective

feedback pins.

8) Place the 2.5V output capacitor, C18 close to the pin

16 of the IC and the 1.5V output capacitor, C17 close

to the Q2 MOSFET.

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.

9) Place R12 and C10 close to pin 23 and R9 and C5

close to pin 9.

10) Place C9 close to pin 12

Component connections:

Note: It is extremely important that no data bus should

be passing through the switching regulator section spe-

cifically close to the fast transition nodes such as PWM

drives or the inductor voltage.

Using the 4 layer board, dedicate one layer to ground,

another layer as the power layer for the 5V, 3.3V, Vcore,

1.5V and if it is possible, for the 2.5V.

Connect all grounds to the ground plane using direct

vias to the ground plane.

Use large low inductance/low impedance plane to con-

nect the following connections either using component

side or the solder side.

a) C14 to Q3 Drain and C3 to Q1 drain

b) Q3 Source to Q4 Drain and Q1 Source to D1

cathode

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

h) C17 to the Q2 source

I) A minimum of 0.2 inch width trace from the C18

capacitor to pin 16

Connect the rest of the components using the shortest

connection possible.

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Data and specifications subject to change without notice. 02/01