iru3038 International Rectifier Corp., iru3038 Datasheet - Page 10

• Manufacturer Part Number: iru3038
• Description: Synchronous Pwm Controller For Termination Power Supply Applications
• Manufacturer: International Rectifier Corp.

IRU3038
6) Place second pole at the ESR zero.
7) Place second zero around the resonant frequency.
8) Use equation (1) to calculate R
These design rules will give a crossover frequency ap-
proximately one-tenth of the switching frequency. The
higher the band width, the potentially faster the load tran-
sient speed. The gain margin will be large enough to
provide high DC-regulation accuracy (typically -5dB to -
12dB). The phase margin should be greater than 458 for
overall stability.
IC Quiescent Power Dissipation
Power dissipation for IC controller is a function of ap-
plied voltage, gate driver loads and switching frequency.
The IC's maximum power dissipation occurs when the
IC operating with single 12V supply voltage (Vcc=12V
and Vc 24V) at 400KHz switching frequency and maxi-
mum gate loads.
This IC's power dissipation results to an excessive tem-
perature rise and should be considered when using
IRU3038 for such an application.
10
F
R
Check if R
If R
F
R
R
P2
Z2
8
6
5
=
=
=
= F
8
= F
is too small, increase R
2p 3 C
2p 3 C
V
ESR
LC
OUT
V
REF
8
- V
>
1
1
10
10
REF
g
3 F
3 F
1
m
3 R
Z2
P2
6
- R
8
7
and start from step 2.
5
:
www.irf.com
Layout Consideration
The layout is very important when designing high fre-
quency switching converters. Layout will affect noise
pickup and can cause a good design to perform with
less than expected results.
Start to place the power components. Make all the con-
nections in the top layer with wide, copper filled areas.
The inductor, output capacitor and the MOSFET should
be close to each other as possible. This helps to reduce
the EMI radiated by the power traces due to the high
switching currents through them. Place input capacitor
directly to the drain of the high-side MOSFET. To reduce
the ESR, replace the single input capacitor with two par-
allel units. The feedback part of the system should be
kept away from the inductor and other noise sources
and be placed close to the IC. In multilayer PCB, use
one layer as power ground plane and have a separate
control circuit ground (analog ground), to which all sig-
nals are referenced. The goal is to localize the high cur-
rent path to a separate loop that does not interfere with
the more sensitive analog control function. These two
grounds must be connected together on the PC board
layout at a single point.
09/12/02
Rev. 2.0