R1211D002A RICOH electronics devices division, R1211D002A Datasheet - Page 12

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

continuous. The continuous current through the inductor is described as Iconst, then,
I
In this moment, the peak current, ILxmax flowing through the inductor and the driver Tr. is described as follows:
ILxmax = Iconst +V
With the formula 4,6, and ILxmax is,
ILxmax = V
Therefore, peak current is more than I
external components should be selected.
In the formula 7, peak current ILxmax at discontinuous mode can be calculated. Put Iconst=0 in the formula.
The explanation above is based on the ideal calculation, and the loss caused by Lx switch and external components
is not included. The actual maximum output current is between 50% and 80% of the calculation. Especially, when the
ILx is large, or V
0.3V) of the diode should be considered.
<Soft-start Operation>
(Step1)
input to OP AMP is also gradually rising. V
voltage is rising up to the setting voltage with input voltage and the ration of R1 and R2. AMPOUT is at “L”, and
switching does not start.
(Step2)
Rev. 1.10
OUT
Soft-start operation is starting from power-on as follows:
The voltage level of SS is rising gradually by constant current circuit of the IC and a capacitor. V
EXT
EXT
TIMING CHART
R1211X002A/R1211X002C
R1211X002B/R1211X002D
= f
OSC
OUT
V
IN
/V
IN
2
IN
is low, the loss of V
t
V
V
ON
IN
I
OUT
OUT
OUT
2
Ton/L
/(2 L (V
R1
R2
R1
R2
+V
IN
Ton/(2 L)
OUT
V
V
FB
FB
-V
VREF
VREF
IN
IN
OUT
))+V
is generated with the on resistance of the switch. As for V
OUT
. Considering the value of ILxmax, the condition of input and output, and
IN
OP AMP
is rising up to input voltage level just after the power-on, therefore, V
Iconst/V
OP AMP
AMPOUT
AMPOUT
- 12 -
OUT
Formula 7
Formula 8
SS
SS
Formula 6
DTC
DTC
PWM Comparator
PWM Comparator
EXT
EXT
OUT,
REF
Vf (as much as
level which is
FB