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參數(shù)資料
| 型號： | R1225N572K-TR |
| 英文描述： | SMPS Controller |
| 中文描述： | 開關(guān)電源控制器 |
| 文件頁數(shù)： | 6/29頁 |
| 文件大小： | 450K |
| 代理商： | R1225N572K-TR |
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Rev. 1.11 - 6 -
voltage.
G
When the threshold level of an external power MOSFET is rather low and the drive-ability of voltage
supplier is small, if the output pin is short circuit, input voltage may be equal or less than UVLO detector
threshold. In this case, the devise is reset with UVLO function that is not the latch-protection function.
G
With the PWM/VFM alternative circuit, when the on duty cycle of switching is 35% or less, the
R1225N alters from PWM mode to VFM mode (Pulse skip mode). The purpose of this circuit is raising
the efficiency with a light load by skipping the frequency and suppressing the consumption current.
However, the ratio of output voltage against input voltage is 35% or less, (ex. Vin>8.6V and Vout=3.0V)
even if the large current may be loaded, the IC keeps its VFM mode. As a result, frequency might be
decreased, and oscillation waveform might be unstable. These phenomena are the typical
characteristics of the IC with PWM/VFM alternative circuit.
The performance of power source circuits using these ICs extremely depends upon the peripheral
circuits.
Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in a
way that the values such as voltage, current, and power of each component, PCB patterns and the IC
do not exceed their respected rated values.
I
How to set the delay time of protection circuit
The equation describes how to calculate the delay time of protection circuit from the value of an external
capacitor C4.
T
DLY
=C4
×
10
6
sec (In this equation, 1000pF
≤
C4
≤
1
μ
F
Without the external capacitor, a certain delay time exists, therefore, if the external capacitor is less than
1000pF, the error will increase. Further, if the external capacitor value is beyond 1
μ
F, the time required to
discharge the C4 will be long, and this may cause the miss-operation. For example, if the protection
circuit may work and released, soon after that the protection may work. In that case, C4 has not
discharged completely yet, therefore, the delay time may be shorter than expected.
PM O S
C3
C2
L
C1
R1
SD
V
IN
CE
CE CONTROL
LOAD
V
OUT
EXT
GND
DLY
C4
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