參數(shù)資料
型號(hào): MB3785APFV
廠商: FUJITSU LTD
元件分類: 穩(wěn)壓器
英文描述: Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities)
中文描述: 0.03 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQFP48
封裝: PLASTIC, LQFP-48
文件頁數(shù): 21/29頁
文件大?。?/td> 293K
代理商: MB3785APFV
21
MB3785A
I
METHOD OF SETTING THE DEAD TIME AND SOFT START
1.
Dead Time
When the device is set for step-up inverted output based on the flyback method, the output transistor is fixed to a
full-on state (ON-duty = 100 %) at power switch-on. To prevent this problem, you may determine the voltages on
the DTC terminals (pins 4, 9, 28, and 33) from the V
REF
voltage so you can easily set the output transistor’s dead
time (maximum ON-duty) independently for each channel as shown below.
(1) CH1 and CH2 Channels
When the voltage on the DTC terminals (pins 4 and 9) is higher than the triangular-wave output voltage from the
oscillator, the output transistor turns off. The dead time calculation formula assuming that triangular-wave amplitude
0.6 V and triangular-wave minimum voltage
1.3 V is given below.
When you do not use these DTC terminals, connect them to GND.
(2) CH3 and CH4 Channels
When the voltage on the DTC terminals (pins 28 and 33) is lower than the triangular-wave output voltage from the
oscillator, the output transistor turns off. The dead time calculation formula assuming that traingular-wave amplitude
0.6 V and triangular-wave maximum voltage
1.9 V is given below.
When you do not use these DTC terminals, connect them to V
REF
.
Duty (OFF) =
×
100 [%], V
dt
=
×
V
REF
V
dt
– 1.3
0.6
R
1
+ R
2
R
2
Figure 9. When Using DTC to Set Dead Time
Figure 10. When Not Using DTC
V
REF
R
1
R
2
DTC1
(DTC2)
Vdt
19
DTC1
(DTC2)
Duty (OFF)
×
100 [%], V
dt
=
×
V
REF
1.9 –V
dt
0.6
R
1
+ R
2
R
2
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