R1215D002F RICOH [RICOH electronics devices division], R1215D002F Datasheet - Page 9

• Manufacturer Part Number: R1215D002F
• Description: STEP-UP DC/DC CONTOLLER
• Manufacturer: RICOH [RICOH electronics devices division]

•
• The feedback voltage is controlled into 1.0V. The output voltage can be set with divider resistors for voltage
Output Voltage is adjustable with setting various resistor values combination.
R1+R2 should be equal or less than 500kΩ
As for the DC/DC converter, depending on the load current and external components such as L and C, phase
may loss around 180°. In such case, phase margin becomes less and may be unstable. To avoid this situation,
make the phase margin more. The pole is made with external components L and C.
C4, C5, R3, and R4 shown in the diagram are for making phase compensation. The gain of the system can be
set with using these resistors and capacitors. Each value in the diagram is just an example.
R4 and C5 make zero (the backward phase).
Choose the R4 and C5 value so as to make the cutoff frequency of this zero point close to the cutoff frequency of
the pole by external components, L and C.
For example, supposed that L=10µH and C
13kHz. Therefore make the cutoff frequency of the zero point close to 13kHz. Then R4=4.7kΩ and C5=2200pF
are appropriate values.
As for setting the gain, the ratio of the composite resistor (RT: RT=R1×R2/(R1+R2)) to R4 is the key.
If the R4 against the composite resistor, R
response characteristic is improved, however, too large gain makes the system be unstable.
If the spike noise of V
may result. In this case, a resistor R3, shown in typical application of the previous page. The recommended
resistance value of R3 is in the range from 1kΩ to 5kΩ. Then, noise level will be decreased.
Further, R1 and C4 makes another zero point (the backward phase).
Make the cutoff frequency of this zero point be lower than the cutoff frequency of the pole by external
components, or, L and C. Herein, R1=160kΩ and C4=1000pF are appropriate values.
• Select the Power MOSFET, the diode, capacitors and the inductor within ratings (Voltage, Current, Power) of
• The soft-start time and the maximum duty cycle setting method
setting, R1 and R2 as shown in typical application of the previous page. Refer to the next formula.
this IC. Choose the power MOSFET with low threshold voltage depending on the input voltage to be able to
turn on the FET completely. Choose the diode with low V
and with fast switching speed. When an external transistor is switching, spike voltage may be generated
caused by an inductor, therefore recommended voltage tolerance of capacitor connected to V
much as the setting voltage or more.
The soft-start time and the maximum duty cycle can be set with R5, R6, and C7 values connected to the
V
Output Voltage Setting Method and Phase Compensation Making Method
REFOUT
pin and the DTC pin. (Refer to the timing chart: Soft-start operation.)
Output Voltage = V
Fpole∼1/{2×π×
Fzero∼1/(2×π×R4×C5)
Fzero∼1/(2×π×R1×C4)
OUT
may be large, the spike noise may be picked into V
(
L ×
FB
C
× (R1+R2)/R2
3
)
}
T,
OUT
is large, the gain becomes also large. If the gain is large, the
(C3) =15µF, the cutoff frequency of the pole is approximately
F
such as Shottky type with low reverse current I
FB
pin, and the unstable operation
OUT
is twice as
R1215D
R
,
9