R1211D002A RICOH electronics devices division, R1211D002A Datasheet - Page 11

• Manufacturer Part Number: R1211D002A
• Description: Step-up DC/DC Controller
• Manufacturer: RICOH electronics devices division

There are two modes, or discontinuous mode and continuous mode for the PWM step-up switching regulator
depending on the continuous characteristic of inductor current.
During on time of the transistor, when the voltage added on to the inductor is described as V
Therefore, the electric power, P
P
With the step-up circuit, electric power is supplied from power source also during off time. In this case, input current is
described as (V
P
In this formula, Tf means the time of which the energy saved in the inductance is being emitted. Thus average
electric power, P
P
In PWM control, when Tf=Toff is true, the inductor current becomes continuos, then the operation of switching
regulator becomes continuous mode.
In the continuous mode, the deviation of the current is equal between on time and off time.
V
Further, the electric power, P
I
When I
Rev. 1.10
OUT
ON
OFF
AV
IN
Output Current and Selection of External Components
IL
=1/(Ton+Toff)
= V
Ton/L=(V
= f
ILxmin
= V
T
0
Tf
0
ON
IN
OSC
OUT
IN
2
t/L dt
(V
Discontinuous Mode
Ton
becomes more than formula 5, the current flows through the inductor, then the mode becomes
OUT
OUT
V
T=1/fosc
IN
OUT
AV
2
-V
-V
T
-V
is described as in the next formula.
IN
T
0
IN
V
ON
ON
) Toff/L
IN
IN
) t/L dt
V
GND
2
2
) t/L, therefore electric power, P
IN
ILxmax
/{2 L (V
t/L dt + V
AV
Formula 1
ON
is equal to output electric power, V
Toff
Tf
OUT
Tf
0
, which is supplied with input side, can be described as in next formula.
IN
Inductor
<Current through L>
-V
i1
(V
IN
OUT
)}=V
t
-V
IN
IN
2
) t/L dt} Formula 3
Lx Tr
T
<Basic Circuit>
Diode
IL
ON
ILxmin
/(2 L V
- 11 -
OFF
Formula 2
Formula 4
Iconst
is described as in next formula.
T=1/fosc
OUT
C
Ton
L
)
Continuous Mode
OUT
V
i2
OUT
I
I
OUT
OUT
, thus,
ILxmax
Formula 5
Toff
IN
t
, the current is V
IN
t/L.