iru3011 International Rectifier Corp., iru3011 Datasheet - Page 11

• Manufacturer Part Number: iru3011
• Description: 5-bit Programmable Synchronous Buck Controller Ic -
• Manufacturer: International Rectifier Corp.

Switcher External Shutdown
The best way to shutdown the part is to pull down on the
soft-start pin using an external small signal transistor
such as 2N3904 or 2N7002 small signal MOSFET. This
allows slow ramp up of the output, the same as the power
up.
Layout Considerations
Switching regulators require careful attention to the lay-
out of the components, specifically power components
since they switch large currents. These switching com-
ponents can create large amount of voltage spikes and
high frequency harmonics if some of the critical compo-
nents are far away from each other and are connected
with inductive traces. The following is a guideline of how
to place the critical components and the connections
between them in order to minimize the above issues.
Start the layout by first placing the power components:
1) Place the input capacitors C3 and the high side
2) Place the synchronous MOSFETs, Q2 and the Q1
3) Place the snubber R4 & C7 between Q1 & Q2.
4) Place the output inductor, L2 and the output capaci-
5) Place the bypass capacitors, C6 and C9 right next to
6) Place the IC such that the PWM output drives, pins
Rev. 1.6
08/20/02
MOSFET, Q1 as close to each other as possible
as close to each other as possible with the intention
that the connection from the source of Q1 and the
drain of the Q2 has the shortest length.
tors, C10 between the MOSFET and the load with
output capacitors distributed along the slot 1 and
close to it.
12V and 5V pins. C6 next to the 12V, pin 18 and C9
next to the 5V, pin 9.
14 and 17 are relatively short distance from gates of
Q1 and Q2.
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Data and specifications subject to change without notice. 02/01
7) If the output voltage is to be adjusted, place resistor
8) Place timing capacitor C7 close to pin 20 and soft-
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 4 layer board, dedicate on layer to Gnd, another
layer as the power layer for the 5V, 3.3V and Vcore.
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.
Connect the rest of the components using the shortest
connection possible.
dividers close to the feedback pin.
Note: Although, the device does not require resistor
dividers and the feedback pin can be directly con-
nected to the output, they can be used to set the
outputs slightly higher to account for any output drop
at the load due to the trace resistance. See the ap-
plication note.
start capacitor C2 close to pin 3.
a) C3 to Q1 Drain
b) Q1 Source to Q2 Drain
c) Q2 drain to L2
d) L2 to the output capacitors, C10
e) C10 to the slot 1
f) Input filter L1 to the C3
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IRU3011
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