R1232D RICOH [RICOH electronics devices division], R1232D Datasheet - Page 10

• Manufacturer Part Number: R1232D
• Description: PWM STEP-DOWN DC/DC CONVERTER WITH SYNCHRONOUS RECTIFIER
• Manufacturer: RICOH [RICOH electronics devices division]

10
•
OPERATION of step-down DC/DC converter and Output Current
energy from the inductor when L
voltage than the input voltage is obtained. The operation will be explained with reference to the following
diagrams:
Step 1: P-channel Tr. turns on and current IL (=i1) flows, and energy is charged into C
Step 2: When P-channel Tr. turns off, Synchronous rectifier N-channel Tr. turns on in order that L maintains IL at
Step 3: IL (=i2) decreases gradually and reaches IL=ILmin=0 after a time period of topen, and N-channel Tr.
with the oscillator frequency (fosc) being maintained constant.
same as those when P-channel Tr. turns on and off.
and the change of the current at OFF.
least, topen is equal toff (topen=toff), and when I
(ILmin>0). The mode is referred to as the continuous mode.
R1232D
The step-down DC/DC converter charges energy in the inductor when L
In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton),
Continuous Conduction Mode
The maximum value (ILmax) and the minimum value (ILmin) of the current flowing through the inductor are the
The difference between ILmax and ILmin, which is represented by ∆I;
Where, t=1/fosc=ton+toff
In Equation 1, V
Even if the output current (I
IL increases from Ilmin (=0) to reach ILmax in proportion to the on-time period (ton) of P-channel Tr.
ILmax, and current IL (=i2) flows.
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).
V
IN
∆I=ILmax−ILmin=V
duty (%)=ton/t×100=ton×fosc×100
topen
Lx Tr
< =
SD
OUT
<Basic Circuits>
toff
×topen/L and (V
i2
OUT
L
OUT
) is, topen < toff as illustrated in the above diagram is not realized with this IC. At
×topen/L=(V
X
transistor is OFF and controls with less energy loss, so that a lower output
CL
i1
IN
−V
OUT
I
V
OUT
OUT
IN
) ×ton/L are respectively shown the change of the current at ON,
−V
OUT
OUT
)×ton/L ........................................................Equation 1
is further increased, ILmin becomes larger than zero
<Current through L>
X
transistor is ON, and discharges the
L
. At this moment,