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參數(shù)資料
| 型號： | US3034CS |
| 廠商： | Unisem Group |
| 英文描述： | 8 PIN PWM SWITCHER CONTROLLER IC |
| 中文描述： | 8引腳的PWM開關控制器IC |
| 文件頁數(shù)： | 9/9頁 |
| 文件大?。?/td> | 74K |
| 代理商： | US3034CS |
US3034
4-9
Rev. 1.8
1/13/99
Switcher Output Voltage Setting
The output voltage can be set using the following
equations.
Assuming , Vo=3.38V and the selected output ripple
is
≈
1.3%(44mV) of the output voltage, a set of
equations are derived that selects the resistor divider
and the hysterises resistor.
Assuming, Rt=1k
, 1%
Rh=(11*Rt)/
Vo
Where:
Rt=Top resistor of the resistor divider
Rh=Hysterises resistor connected between pins 3 and
4 of the US3034
Vo=Selected output ripple (typically 1% to 2% of
output voltage)
Assuming,
Vo=44mV
Rh=(11*1000)/0.044=250 k
Select Rh=249 k
, 1%
The bottom resistor of the divider is then calculated
using the following equations:
Rb=Rt/X
Where:
Rb=Bottom resistor of the divider
X=
[
(Vo + (
Vo/2))/Vref
]
- 1
Vref=1.25 V typ.
X=
[
(3.38+ (0.044/2))/1.25
]
- 1 = 1.72
Rb=1000/1.72=580
Select Rb=576
, 1%
Frequency Calculation
The US3034 frequency of operation is calculated using
the following formula:
Fs=
[
(Vo*(1-D)*ESR)
]
/(L*
Vo) (MHz)
Where:
Vo=Output voltage (V)
D=Duty cycle
ESR=Output capacitor ESR (V)
L=Output inductance (uH)
Vo=Output ripple voltage (V)
For our example:
D
≈
(Vo + Vf)/Vin
Where, Vf=Forward voltage drop of the Schotky diode
D=(3.38 + 0.5)/5=0.78
The ESR=18m
for 2 of the Sanyo 1500uF,
6MV1500GX caps. If L=3.5uH then, Fs is calculated
as follows:
Fs=
[
(3.38*(1-0.78)*0.018)
]
/(3.5*0.044)= 0.087 Mhz =
87 kHz
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