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參數(shù)資料
| 型號： | US3007 |
| 廠商： | Unisem Group |
| 英文描述： | 5 BIT PROGRAMMABLE SYNCHRONOUS BUCK PLUS NON SYNCHRONOUS , LDO CONTROLLER AND 200MmA LDO ON BOARD |
| 中文描述： | 5位可編程同步降壓加上非同步，LDO控制器及船上200MmA穩(wěn)壓器 |
| 文件頁數(shù)： | 12/15頁 |
| 文件大?。?/td> | 101K |
| 代理商： | US3007 |
4-12
Rev. 1.8
12/8/00
US3007
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 too small , the output ripple current and ripple
voltage become too large. One solution 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 following set of formulas are
derived to achieve the optimum performance without
many design iterations.
The maximum output inductance is calculated using the
following equation :
L = ESR * C * ( Vinmin - Vomax ) / ( 2*
I )
Where :
Vinmin = Minimum input voltage
For Vo = 2.8 V ,
I = 14.2 A
L =0.006 * 9000 * ( 4.75 - 2.8) / (2 * 14.2) = 3.7 uH
Assuming that the programmed switching frequency is
set at 200 KHZ , 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 wounded
with 8 Turns of # 16 AWG wire, resulting in 3 uH
inductance with
≈
3 m
of DC resistance.
Assuming L = 3 uH and the switching frequency ; Fsw =
200 KHZ , the inductor ripple current and the output
ripple voltage is calculated using the following set of
equations :
T = 1/Fsw
T
≡
Switching Period
D
≈
( Vo + Vsync ) / ( Vin - Vsw + Vsync )
D
≡
Duty Cycle
Ton = D * T
Vsw
≡
High side Mosfet ON Voltage = Io * Rds
Rds
≡
Mosfet On Resistance
Toff = T - Ton
Vsync
≡
Synchronous MOSFET ON Voltage=Io * Rds
Ir = ( Vo + Vsync ) * Toff /L
Ir
≡
Inductor Ripple Current
Vo =
Ir * ESR
Vo
≡
Output Ripple Voltage
In our example for Vo = 2.8V and 14.2 A load , Assum-
ing IRL3103 MOSFET for both switches with maximum
on resistance of 19 m
, we have :
T = 1 / 200000 = 5 uSec
Vsw =Vsync= 14.2*0.019=0.27 V
D
≈
( 2.8 + 0.27 ) / ( 5 - 0.27 + 0.27 ) = 0.61
Ton = 0.61 * 5 = 3.1 uSec
Toff = 5 - 3.1 = 1.9 uSec
Ir = ( 2.8 + 0.27 ) * 1.9 / 3 = 1.94 A
Vo = 1.94 * .006 = .011 V = 11 mV
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.
Dmax
≈
( 2.8 + 0.27 ) / ( 4.75 - 0.27 + 0.27 ) = 0.65
Pdh = Dmax * Io^2*Rds(max)
Pdh= 0.65*14.2^2*0.029=3.8 W
Rds(max)=Maximum Rds-on of the MOSFET at 125
°
C
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
Pds = (1-Dmin)*Io^2*Rds(max)
Pds=(1 - 0.43) * 14.2^2 * 0.029 = 3.33 W
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 equation below, Vf=0.5V
Dmax
≈
( 3.3 + 0.5 ) / ( 4.75 - 0.27 + 0.5 ) = 0.76
Pdh = Dmax * Io^2*Rds(max)
Pdh= 0.76*10^2*0.029=2.21 W
Rds(max)=Maximum Rds-on of the MOSFET at 125
°
C
For diode, the maximum power dissipation happens at
minimum Vo and minimum duty cycle.
Dmin
≈
( 3.3 + 0.5 ) / ( 5.25 - 0.27 + 0.5 ) = 0.69
Pdd = (1-Dmin)*Io*Vf=(1 - 0.69) * 10 * 0.5 = 1.55 W
Switcher Current Limit Protection
The US3007 uses the MOSFET Rds-on as the sensing
resistor to sense the MOSFET current and compares to
a programmed voltage which is set externally via a re-
sistor (Rcs) placed between the drain of the MOSFET
and the “CS+” terminal of the IC as shown in the appli-
cation circuit.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| US3007CW | 制造商:UNISEM 制造商全稱:UNISEM 功能描述:5 BIT PROGRAMMABLE SYNCHRONOUS BUCK PLUS NON SYNCHRONOUS , LDO CONTROLLER AND 200MmA LDO ON BOARD |
| US3008 | 制造商:UNITPOWER 制造商全稱:UNITPOWER 功能描述:N-Ch 30V Fast Switching MOSFETs |
| US-3008 | 功能描述:PROTO-BOARD 8PIN THRU-HOLE SIP RoHS:是 類別:原型開發(fā)產(chǎn)品 >> 適配器，可互換接口板 系列:3000, UNI-SIP™ 標(biāo)準(zhǔn)包裝:1 系列:- 原型板類型:- Package Accepted:- 尺寸/尺寸:- 位置數(shù):- 孔直徑:- 板厚度:- 材質(zhì):- |
| US3010 | 制造商:UNISEM 制造商全稱:UNISEM 功能描述:5 BIT PROGRAMMABLE SYNCHRONOUS BUCK CONTROLLER IC |
| US-3010 | 功能描述:PROTO-BOARD 10PIN THRU-HOLE SIP RoHS:是 類別:原型開發(fā)產(chǎn)品 >> 適配器，可互換接口板 系列:3000, UNI-SIP™ 標(biāo)準(zhǔn)包裝:1 系列:- 原型板類型:- Package Accepted:- 尺寸/尺寸:- 位置數(shù):- 孔直徑:- 板厚度:- 材質(zhì):- |
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