參數(shù)資料
型號: R1230D211F-TR
廠商: RICOH COMPANY LTD
元件分類: 穩(wěn)壓器
英文描述: SWITCHING REGULATOR, 920 kHz SWITCHING FREQ-MAX, PDSO8
封裝: 0.9 MM HEIGHT, SON-8
文件頁數(shù): 3/26頁
文件大?。?/td> 284K
代理商: R1230D211F-TR
R1230D
11
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 en-
ergy 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
i2
L
CL
Nch Tr
VIN
IOUT
VOUT
i1
IL
ILmax
ILmin
topen
T=1/fosc
ton
toff
Step 1:
P-channel Tr. turns on and current IL (=i1) flows, and energy is charged into CL. At this moment, IL in-
creases 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).
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.
Discontinuous Conduction Mode and Continuous Conduction Mode
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 = ILmax - ILmin = VOUT × topen / L = (VIN - VOUT) × 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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