R1211X Datasheet, PDF (10/33 Pages) RICOH electronics devices division – Step-up DC/DC Controller

q Use a 1µF or more capacitance value of bypass capacitor between VIN pin and GND, C1 as shown in the typical
applications above.
q In terms of the capacitor for setting delay time of the latch protection, C2 as shown in typical applications of the
previous page, connect between Delay pin and GND pin of the IC with the minimum wiring distance.
q Connect a 1µF or more value of capacitor between VOUT and GND, C3 as shown in typical applications of the
previous page. (Recommended value is from 10µF to 22µF.) If the operation of the composed DC/DC converter may
be unstable, use a tantalum type capacitor instead of ceramic type.
q Connect a capacitor between VOUT and the dividing point, C4 as shown in typical applications of the previous page.
The capacitance value of C4 depends on divider resistors for output voltage setting. Typical value is between 100pF
and 1000pF.
q Output Voltage can be set with divider resistors for voltage setting, R1 and R2 as shown in typical applications of
the previous page. Refer to the next formula.
Output Voltage = VFB×(R1+R2)/R2
R1+R2=100kΩ is recommended range of resistances.
q The operation of Latch protection circuit is as follows: When the IC detects maximum duty cycle, charge to an
external capacitor, C2 of DELAY pin starts. And maximum duty cycle continues and the voltage of DELAY pin
reaches delay voltage detector threshold, VDLY, outputs “L” to EXT pin and turns off the external power MOSFET.
To release the latch protection operation, make the IC be standby mode with CE pin and make it active in terms of
B/D version. Otherwise, restart with power on.
The delay time of latch protection can be calculated with C2, VDLY, and Delay Pin Charge Current, IDLY1, as in the
next formula.
t=C2×VDLY/IDLY1
Once after the maximum duty is detected and released before delay time, charge to the capacitor is halt and delay
pin outputs “L”.
q As for R1211X002A/C version, the values and positioning of C4, C5, R3, and R4 shown in the above diagram are
just an example combination. These are for making phase compensation. If the spike noise of VOUT may be large,
the spike noise may be picked into VFB pin and make the operation unstable. In this case, a resistor R3, shown in
typical applications of the previous page. The recommended resistance value of R3 is in the range from 10kΩ to
50kΩ. Then, noise level will be decreased.
q As for R1211X002B/D version, EXT pin outputs GND level at standby mode.
q Select the Power MOSFET, the diode, and the inductor within ratings (Voltage, Current, Power) of this IC. Choose
the power MOSFET with low threshold voltage depending on Input Voltage to be able to turn on the FET completely.
Choose the diode with low VF such as Shottky type, and with low reverse current IR, 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 VOUT is three times of setting voltage or more.
✩The performance of power circuit with using this IC depends on external components. Choose the most suitable
components for your application.
Rev. 1.10
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