參數(shù)資料
型號： IRU3018CW
廠商： International Rectifier
英文描述： 5-BIT PROGRAMMABLE SYNCHRONOUS BUCK PLUS LDO CONTROLLER AND 200mA LDO ON-BOARD
中文描述： 5位可編程同步降壓普樂士LDO控制器和200mA LDO的板載
文件頁數(shù)： 12/16頁
文件大小： 148K
代理商： IRU3018CW
12
Rev. 1.5
07/24/01
IRU3018
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 inductor is too small, the output ripple
current and ripple voltage become too large. One solu-
tion to bring the ripple current down is to increase the
switching frequency, however that will be at the cost of
reduced efficiency and higher system cost. The follow-
ing set of formulas are derived to achieve the optimum
performance without many design iterations.
The maximum output inductance is calculated using the
following equation:
Where :
Vin(min) = Minimum input voltage
For Vo=2.8V,
I=14.2A
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 3
μ
H inductance with
≈
3m
of DC resistance.
Assuming L=3
μ
H and Fsw=200KHz (switching fre-
quency), the inductor ripple current and the output ripple
voltage is calculated using the following set of equations:
In our example for Vo=2.8V and 14.2 A load, assuming
IRL3103 MOSFET for both switches with maximum on
resistance of 19m
, we have:
Power Component Selection
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.
For synch MOSFET, maximum power dissipation hap-
pens at minimum Vo and minimum duty cycle.
Dmin
≈
(2 + 0.27) / (5.25 - 0.27 + 0.27) = 0.43
P
DS
= (1-Dmin)
×
Io
2
×
R
DS(max)
P
DS
= (1 - 0.43)
×
14.2
2
×
0.029 = 3.33 W
Heat Sink Selection
Selection of the heat sink is based on the maximum
allowable junction temperature of the MOSFETS. Since
we previously selected the maximum R
DS(on)
at 125
!
C,
then we must keep the junction below this temperature.
Selecting TO-220 package gives
θ
JC
=1.8
!
C/W (from the
venders’ data sheet) and assuming that the selected
heat sink is black anodized, the heat-sink-to-case ther-
mal resistance is:
θ
cs=0.05
!
C/W, the maximum heat
sink temperature is then calculated as:
With the maximum heat sink temperature calculated in
the previous step, the heat-sink-to-air thermal resistance
(
θ
SA
) is calculated as follows:
Assuming T
A
= 35
!
C:
T = Ts - T
A
= 118 - 35 = 83
!
C
Temperature Rise Above Ambient
L = ESR
×
C
×
[Vin(min) - Vo(max)] / ( 2
×
I )
L = 0.006
×
9000
×
(4.75 - 2.8) / (2
×
14.2) = 3.7
μ
H
T = 1 / 200000 = 5
μ
s
Vsw = Vsync = 14.2
×
0.019 = 0.27V
D
≈
(2.8 + 0.27) / (5 - 0.27 + 0.27) = 0.61
Ton = 0.61
×
5 = 3.1
μ
s
Toff = 5 - 3.1 = 1.9
μ
s
Ir = (2.8 + 0.27)
×
1.9 / 3 = 1.94A
Vo = 1.94
×
0.006 = 0.011V = 11mV
T
≡
Switching Period
D
≡
Duty Cycle
Vsw
≡
High-side MOSFET ON Voltage
R
DS
≡
MOSFET On-resistance
Vsync
≡
Synchronous MOSFET ON Voltage
Ir
≡
Inductor Ripple Current
Vo
≡
Output Ripple Voltage
T = 1 / Fsw
Vsw = Vsync = Io
×
R
DS
D
≈
(Vo + Vsync) / (Vin - Vsw + Vsync)
Ton = D
×
T
Toff = T - Ton
Ir = (Vo + Vsync)
×
Toff / L
Vo =
Ir
×
ESR
Dmax
≈
(2.8 + 0.27) / (4.75 - 0.27 + 0.27) = 0.65
P
DH
= Dmax
×
Io
2
×
R
DS(max)
P
DH
= 0.65
×
14.2
2
×
0.029 = 3.8W
R
DS(max)
= Maximum R
DS(on)
of the MOSFET at 125
!
C
Ts = T
J
- P
D
×
(
θ
JC
+
θ
cs)
Ts = 125 - 3.82
×
(1.8 + 0.05) = 118
!
C
θ
SA
=
T / P
D
=
83 / 3.82 = 22
!
C/W
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IRU3021MCWTR 功能描述:IC CTRL/REG SYNC BUCK 28-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 專用型 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,000 系列:- 應(yīng)用:電源，ICERA E400，E450 輸入電壓:4.1 V ~ 5.5 V 輸出數(shù):10 輸出電壓:可編程 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:42-WFBGA，WLCSP 供應(yīng)商設(shè)備封裝:42-WLP 包裝:帶卷 (TR)
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