R1211D002B RICOH [RICOH electronics devices division], R1211D002B Datasheet - Page 10

• Manufacturer Part Number: R1211D002B
• Description: STEP-UP DC/DC CONTROLLER
• Manufacturer: RICOH [RICOH electronics devices division]

10
Output Current and Selection of External Components
depending on the continuous characteristic of inductor current.
V
current is described as (V
electric power, P
switching regulator becomes continuous mode.
R1211x
IN
There are two modes, or discontinuous mode and continuous mode for the PWM step-up switching regulator
During on time of the transistor, when the voltage added on to the inductor is described as V
With the step-up circuit, electric power is supplied from power source also during off time. In this case, input
In this formula, Tf means the time of which the energy saved in the inductance is being emitted. Thus average
In PWM control, when Tf = Toff is true, the inductor current becomes continuos, then the operation of
In the continuous mode, the deviation of the current is equal between on time and off time.
Further, the electric power, P
P
P
P
I
V
×t/L. Therefore, the electric power, P
OUT
ON
OFF
AV
IN
× T
=
=
=
=
1/(T
f
∫
OSC
∫
IL
0
ON
Ton
V
ILxmin
Tf
0
/L
IN
ON
×
V
2
V
IN
+
=
×
IN
×
T
t/L
AV
(V
2
Discontinuous Mode
(V
Ton
OFF
×
is described as in the next formula.
T=1/fosc
OUT
OUT
dt
T
)
ON
×
.............................................................................................................................. Formula 1
−
−
{
2
∫
V
/
V
{
OUT
0
Ton
IN
2
IN
)
×
ILxmax
)
V
×
L
− V
×
IN
t/L
×
AV
2
Toff/L
(V
IN
×
dt
is equal to output electric power, V
) ×t/L, therefore electric power, P
Toff
t/L
OUT
Tf
........................................................................................................ Formula 2
GND
dt
−
V
IN
ON
V
................................................................................................... Formula 4
+
IN
, which is supplied with input side, can be described as in next formula.
∫
)
}
Tf
0
=
t
V
<Circuit through L>
V
Inductor
IN
IN
<Basic Circuit>
×
2
i1
(V
×
OUT
T
ON
−
/(2
L
Diode
V
X
×
IN
Tr
L
)
×
×
t/L
V
CL
OUT
i2
dt}
OFF
V
IL
)
OUT
OUT
ILxmin
.................................................... Formula 5
................................................... Formula 3
is described as in next formula.
I
× I
OUT
OUT
Iconst
Continuous Mode
T=1/fosc
, thus,
Ton
ILxmax
Toff
IN
, the current is
t