IRU3007CW International Rectifier, IRU3007CW Datasheet - Page 12

• Manufacturer Part Number: IRU3007CW
• Description: IC CTRL/REG SYNC BUCK 28-SOIC
• Manufacturer: International Rectifier

Specifications of IRU3007CW

• Applications: Controller, Intel Pentium® II
• Voltage - Input: 5V, 12V
• Number Of Outputs: 4
• Voltage - Output: 1.3 ~ 3.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *IRU3007CW; IRU3007-CW; IRU3007-CW

IRU3007
of the 1500mF, 6MV1500GX type Sanyo capacitors. With
Rs=5mV, the maximum ESR becomes 9.5mV which is
equivalent to
is that if a trace is being used to implement the resistor,
the power dissipated by the trace increases the case
temperature of the output capacitors which could seri-
ously affect the life span of the output capacitors.
Output Inductor Selection
The output inductance must be selected such that un-
der low line and the maximum output voltage condition,
the inductor current slope times the output capacitor
ESR is ramping up faster than the capacitor voltage is
drooping during a load current step. However, if the in-
ductor is made too small, the output ripple current and
ripple voltage will become too large. One solution to bring
the ripple current down is to increase the switching fre-
quency, however that will be at the cost of reduced effi-
ciency and higher system cost. The following set of for-
mulas are derived to achieve optimum performance with-
out many design iterations.
The maximum output inductance is calculated using the
following equation:
Assuming that the programmed switching frequency is
set at 200KHz, an inductor is designed using the
Micrometals’ powder iron core material. The summary
of the design is outlined below:
The selected core material is Powder Iron, the selected
core is T50-52D from Micro Metal wound with 8 turns of
#16 AWG wire, resulting in 3mH inductance with 3 mV
of DC resistance.
Assuming L=3mH and Fsw=200KHz (switching fre-
quency), the inductor ripple current and the output ripple
voltage is calculated using the following set of equations:
12
L = ESR 3 C 3
Where:
V
For Vo = 2.8V and DI = 14.2A, we get:
L = 0.006 3 9000 3
T
D
Vsw
R
Vsync
DIr
DVo Output Ripple Voltage
IN(MIN)
DS
Switching Period
Duty Cycle
Inductor Ripple Current
MOSFET On-Resistance
High-side MOSFET ON Voltage
= Minimum input voltage
Synchronous MOSFET ON Voltage
4 caps. Another important consideration
(V
IN(MIN)
(4.75 - 2.8)
(2 3 14.2)
(2 3 DI)
- Vo
(MAX)
= 3.7mH
)
www.irf.com
In our example for Vo = 2.8V and 14.2 A load, assuming
IRL3103 MOSFET for both switches with maximum on
resistance of 19m V, we have:
Power Component Selection
Vcore
Assuming IRL3103 MOSFETs as power components,
we will calculate the maximum power dissipation as fol-
lows:
For high side switch the maximum power dissipation
happens at maximum Vo and maximum duty cycle.
R
For synch MOSFET, maximum power dissipation hap-
pens at minimum Vo and minimum duty cycle.
3.3V Supply
Again, for high side switch the maximum power dissipa-
tion happens at maximum Vo and maximum duty cycle.
The duty cycle equation for non synchronous replaces
the forward voltage of the diode with the Synch MOSFET
on voltage. In equations below:
DS(MAX)
T = 1 / Fsw
Vsw = Vsync = Io3R
D
T
T
DIr = (Vo + Vsync)3T
DVo = DIr3ESR
T = 1 / 200000 = 5ms
Vsw = Vsync = 14.230.019 = 0.27V
D
T
T
DIr = (2.8 + 0.27)31.9 / 3 = 1.94A
DVo = 1.9430.006 = 0.011V = 11mV
D
P
P
D
P
P
Vf = 0.5V
D
ON
OFF
ON
OFF
MAX
DH
DH
MIN
DS
DS
MAX
=Maximum R
= D3T
= 0.6135 = 3.1ms
(Vo + Vsync) / (V
(2.8 + 0.27) / (5 - 0.27 + 0.27) = 0.61
= (1 - D
= (1 - 0.43)314.2
= D
= 0.65314.2
= T - T
= 5 - 3.1 = 1.9ms
(2 + 0.27) / (5.25 - 0.27 + 0.27) = 0.43
(2.8 + 0.27) / (4.75 - 0.27 + 0.27) = 0.65
(3.3 + 0.5) / (4.75 - 0.27 + 0.5) = 0.76
MAX
3Io
MIN
ON
)3Io
2
3R
DS(ON)
2
30.029 = 3.8W
2
DS(MAX)
3R
IN
DS
2
OFF
of the MOSFET at 1258C
30.029 = 3.33W
DS(MAX)
- Vsw + Vsync)
/ L
08/20/02
Rev. 2.1