iru3055 International Rectifier Corp., iru3055 Datasheet - Page 14

• Manufacturer Part Number: iru3055
• Description: 5-bit Programmable 3-phase Synchronous Buck Controller Ic -
• Manufacturer: International Rectifier Corp.

IRU3055
Design Example
In the demo-board, the condition is as follows:
Output voltage regulation is within 100mV during tran-
sient.
(1) Select Switching Frequency
(2) Soft-Start Capacitor
(3) Output Inductor and Capacitor
(4) Senseless Inductor Current Sensing
14
L>V
L>1.53(12-1.5)/(150K312340%360A/3)=1.1mH
According to Figure 10 and equation (5), the oscilla-
tor selection resistor is given by:
For 1.5V output, V
the converter can be estimated from equation (4):
If t
Select the current ripple LIR=40%, by equation (7):
Select core from Micrometal, T60-18 with 6 turns
#14 AWG wire, which gives 1mH inductor, 15A RMS
and 25A saturation current. The DC resistor of in-
ductor is 1.6mV.
The output capacitor is based on ESR. Suppose
the maximum allowed voltage droop for 60A load is:
Select 8 Panasonic capacitors. EEUFJ0J272U with
2700mF and 13mV ESR each. The total:
With equation (1), we select the inductor sensing
network which has a time constant:
Select R2, R4 and R5 = 1.5K
START
Fs = 150KHz for each phase
Rt
From Figure 10, select Rt=47K
t
Css = 20ms310mA/(1.5V+0.7V) = 95nF
Choose Css=0.1mF
OUT
L = 1mH and R
DV = 100mV
ESR < DV/Di = 100mV/60A = 1.66mV
C
ESR = 13mV/8 = 1.6mV
R23C8 = 23L/R
Select: C8 = 1mF
R2 = 231mH/(1.6mV31uF) = 1.25K
V
START
OUT
IN
=20ms, then:
3(V
=12V, V
= 832700mF = 21600mF
7500/150 = 50K
= (V
IN
-V
SET
OUT
OUT
+0.7V)3Css/10mA
)/(Fs3V
=1.5V and I
L
SET
= 1.6mV
L
=1.5V. The soft-start time of
IN
3LIR3I
OUT
=60A
OUT
/m)
www.irf.com
(5) MOSFET Selection
(6) Over Current Setting
(7) Compensation Design
By equation (9), the RMS current of high side
MOSFET is given as:
Select MOSFET from International Rectifier
IRF3704S with D-2 pak, which will result to:
For low side MOSFET:
Select MOSFET from International Rectifier
IRF3711S with D-2 package, which will result to:
By equation (3), over current limit is set by R
current limit should be at least 150% of the nominal
output current. Set I
For low side MOSFET, R
1508C. The over current setting resistor is given by:
For detailed explanation, please see IRU3037 data
sheet. Select bandwidth of the system to be 1/10 of
switching frequency that is 15KHz:
The compensation resistor can be calculated as:
Where Vosc is the ramp peak voltage and g
transconductance of the error amplifier. From the
data sheet:
Rc = 2394KHz31mH/(1231.6mV3720mmho)
Rc = 12KV. Select R6=Rc=12.7KV
The compensator capacitor is given as:
I
I
D = 1.5/12 = 0.125
I
R
I
D = V
I
R
R
R
Select R
Fo = 233.14315KHz = 94KHz
Rc = Vosc3Fo3L/(V
Vosc = 2V
g
Cc =
Cc =
Select C12=Cc=22nF
RMS(HI)
RMS(HI)
RMS
RMS(LO)
RMS(LO)
m
RDS(ON)
DS(ON)(LO)
SET
SET
= 720mmho
=
= I
= 90A39mV/3/160mA = 1.7KV
OUT
=
=
=
=
MAX
(L3C
= 9mV and 110A I
(1mH321600mF) /0.75/12KV = 16.3nF
0.125360A/3 = 7.1A
SET
/V
= 6mV and 110A current
3R
(V
D3I
(1-D)3I
(1-0.125)360/3 = 19A
IN
= 2.2KV
OUT
= 1.5/12 = 0.125
OUT
DS(ON)
MAX
OUT
/V
) /0.75/Rc
=90A and 30A for each phase.
/m
IN
OUT
/3/160mA
)3I
/m
DS(ON)
IN
OUT
3ESR3g
/m
DS
=6mV and 9mV at
current
m
)
SET
08/13/02
m
Rev. 1.4
is the
. The