DC/DC Converter

Ricoh DC/DC converters may use PWM control or VFM control. PWM is an abbreviation for Pulse Width Modulation and VFM is an abbreviation for Variable Frequency Modulation.
For optimal use, some products may be switched between the two types of control, and the switching methods include manual switching by means of a MODE pin and automatic switching.
The automatic switching method switches from PWM control to VFM control whe the duty ratio decreases below a specified value (VFM duty: 35% etc.).
When switching needs to be performed according to conditions other than
the duty ratio please make use of the manual switching type.

Ricoh DC/DC converters include converters both with and without in-built output transistor. The former have an Lx pin, the latter an EXT pin and they are respectively referred to as DC/DC converters and DC/DC controllers. (If a single product has both types it is listed as a DC/DC converter)
When using an external output transistor, please use a power MOS FET. When efficiency during high loads is more important please use a MOS FET with a low ON resistance, but when efficiency during low loads is more important please use a MOS FET with a small gate capacity.Please use a MOS FET that has a maximum drain current higher than the maximum coil current (ILmax).

Ricoh DC/DC converters include types in which the output voltage is fixed within the IC and types that allow the output voltage to be set with an external resistor. The types in which the output voltage is fixed within the IC have a VOUT pin, while the externally settable products have a VFB pin. When using an externally settable type please select components with attention to a phase compensation and intrusion of noise. (Within the RN5RY settable type series, RN5RY202 is listed as having a VOUT pin rather than a VFB pin)

To provide more stable operation some DC/DC converters contain a UVLO (Under Voltage Lock Out) function. After turning on power, the UVLO function keeps the internal circuit in the standby state until the DC/DC converter input voltage (VIN) reaches the UVLO voltage, so as to reduce supply current and avoid misoperation.

Products Containing Under Voltage Lockout Function
R1200x	R1201x	R1211x	R1212D	R1215D
R1218x	R1224N	R1225N	R1232D	R1234D
R5210x	R5212D	R5220x	R1280D002x	R1282D002A
R1283x	R1285L	R1290K	R1240x	R1242S
RP901x	RP902x

Start is a function that operateswhen the input voltage (VIN) reaches the minimum operating voltage and UVLO voltage after power on, so as to prevent a sudden starting up of the DC/DC converter that could cause a rush current and over/under shoots of output voltage.
The DC/DC converter is made to start up in a gradual manner by provision of a start up time (soft start time). This soft start time is fixed within the IC, but along with the later to be explained oscillator maximum duty cycle setting, in some products it may be set externally.

Products Containing Soft Start Function
R1200x	R1211x	R1212D	R1215D	R1218x
R1224N	R1225N	R1232D	R1234D	R5210x
R5212D	R5220x	R1280D002x	R1282D002A	R1283x
R1285L	R1290K	R1240x	R1242S	RP901x
RP902x	RP400x

Some products allow the oscillator maximum duty cycle to externally set by a capacitor and resistors connected to the DTC pin and VREFOUT pin. The soft start function can also be set externally.

Products with Externally Settable Oscillator Maximum Duty Cycle
R1212D	R1215D	R1280D002x	R1282D002A
R1290K

The protection circuits in Ricoh DC/DC converters can be either latch type or reset type. Latch type protection circuits latch the power MOS to the OFF state during high load etc. if the oscillator maximum duty cycle persists for a specified time (the protection delay time). The latch protective circuit can be released by putting the regulator into the standby mode with the CE pin and then into the active mode, or, by turning the power off and back on.
The protection delay time can be set by the size of a capacitor connected t the DLY pin (DELAY pin).
Reset type protection circuits repeatedly trigger the soft start operation so as to restrict output current during high load etc. if the oscillator maximum duty cycle persists for a specified time (the protection delay time). The reset protection circuit is automatically released following removal of the high load etc. that is causing the maximum duty to occur. The protection delay time is fixed within the IC.
DC/DC products which has Fold back type protection circuit, keep operating at short condition with lower operating frequency and limiting the Lx current.

Products Containing Latch Type Protection Circuit
R1211x	R1212D	R1215D	R1225N	R1232D
R1234D	R5220x	R1280D002x	R1282D002A
R1283x	R1285L	R1290K	R1240x	R1242S

Products Containing Reset Type Protection Circuit
R1224N	RP901x	RP902x

Products Fold Back Type Protection Circuit

R1240x R1242S

The phase compensation of some DC/DC converters can be set with external components. Please set the phase compensation of such products by connecting external capacitor (speed up capacitor) and resistor to the AMPOUT pin.

Products Allowing External Phase Compensation
R1211x	R1212D	R1215D	R1283x	R1290K

The R1210Nxx1A PWM controlled DC/DC Step-up Converters contain a frequency switching circuit. When output loads become light, the PWM control oscillator frequency is reduced from 100kHz to 35kHz. This reduces supply current.

Products Containing a Frequency Switching Circuit

R1210Nxx1

R1218x contains OVP (Over Voltage Protection). This circuit monitors the VOUT pin voltage and if it reaches the OVP voltage it will stop oscillation. When the VOUT pin voltage decreases it will restart oscillation, but if the cause of the excess VOUT pin voltage is not removed the OVP circuit will operate repeatedly so as to restrict the VOUT pin voltage.

R1218x062A OVP Transient Characteristic (OVP detection voltage = 27.5V)

Products Containing Over Voltage Protection (OVP)

R1200x R1201x R1218x