R1212D002A RICOH [RICOH electronics devices division], R1212D002A Datasheet - Page 12

• Manufacturer Part Number: R1212D002A
• Description: STEP-UP DC/DC CONTOLLER
• Manufacturer: RICOH [RICOH electronics devices division]

12
Output Current and Selection of External Components
depending on the continuous characteristic of inductor current.
V
formula.
current is described as (V
electric power, or P
regulator becomes continuous mode.
R1212D
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 switching
× t/L. Therefore, the electric power, P
IL
ILxmin
P
P
P
ON
OFF
AV
Ton
=
=
=
T=1/fosc
1/ton
Discontinuous Mode
1
∫
/(
∫
0
Ton
V
AV
0
T
V
Tf
IN
ON
is described as in the next formula.
IN
2
×
+
×
(
T
OUT
t
V
L /
OFF
V
OUT
ILxmax
IN
− V
dt
)
×
−
.....................................................................................................Formula 1
{
IN
V
∫
) ×t/L, therefore electric power, P
0
IN
Ton
V
)
Toff
×
IN
Tf
2
t
×
L /
t
Inductor
L /
dt
ON
, which is supplied with input side, can be described as in next
dt
<Circuit through L>
................................................................................Formula 2
i1
<Basic Circuit>
+
∫
t
0
Tf
V
IN
×
(
Diode
V
Lx Tr
OUT
−
V
IL
IN
ILxmin
)
OFF
×
t
is described as in next formula.
L /
CL
dt
i2
Iconst
}
Continuous Mode
V
...............................Formula 3
OUT
T=1/fosc
1/ton
Ton
I
OUT
ILxmax
IN
Toff
, the current is