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參數(shù)資料
| 型號： | R5220D111A-TR |
| 廠商： | RICOH COMPANY LTD |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 1440 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封裝： | 0.85 MM HEIGHT, TSON-6 |
| 文件頁數(shù)： | 20/22頁 |
| 文件大小： | 627K |
| 代理商： | R5220D111A-TR |
R5220D
7
OPERATION of step-down DC/DC converter and Output Current
The step-down DC/DC converter charges energy in the inductor when LX transistor is ON, and discharges the
energy from the inductor when LX transistor is OFF and controls with less energy loss, so that a lower output
voltage than the input voltage is obtained. The operation will be explained with reference to the following
diagrams:
<Basic Circuits>
<Current through L>
Pch Tr
Nch Tr
i2
i1
L
CL
IOUT
VOUT
VIN
ILmax
ILmin
IL
topen
ton
T=1/fosc
toff
Step 1: P-channel Tr. turns on and current IL (
=i1) flows, and energy is charged into CL. At this moment, IL
increases from ILmin (
=0) to reach ILmax in proportion to the on-time period (ton) of P-channel Tr.
Step 2: When P-channel Tr. turns off, Synchronous rectifier N-channel Tr. turns on in order that L maintains IL
at ILmax, and current IL (
=i2) flows.
Step 3: IL (
=i2) decreases gradually and reaches IL=ILmin=0 after a time period of topen, and N-channel Tr.
Turns off. Provided that in the continuous mode, next cycle starts before IL becomes to 0 because toff
time is not enough. In this case, IL value increases from this ILmin (>0).
I In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton), with
the oscillator frequency (fosc) being maintained constant.
The maximum value (ILmax) and the minimum value (ILmin) of the current flowing through the inductor are the
same as those when P-channel Tr. turns on and off.
The difference between ILmax and ILmin, which is represented by I;
I=ILmaxILmin=VOUT×topen/L=(VINVOUT)×ton/L........................................................ Equation 1
wherein, T
=1/fosc=ton+toff
duty (%)
=ton/T×100=ton×fosc×100
topen <
= toff
In Equation 1, VOUT
×topen/L and (VIN VOUT) ×ton/L respectively show the change of the current at "ON", and the
change of the current at "OFF".
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