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Application Note
DC/DC Converter Application Note
Technical Information about Ricoh DC/DC converters.
In the beginning
Ricoh has a superior DC/DC converter lineup for low input voltage and high input voltage, small output current and large output current.
Our portfolio includes products such as: step-up, step-down and products with multiple outputs, all are manufactured by CMOS
technology to ensure low supply current.
40V
Step-up
Step-down
Multipul Outputs
High Voltage
20V
Middle Voltage
6V
Low Voltage
For Display Panel
For White LED Backlight
PMOLED
Step-up for
General Use
R1240 Group
R1224N
R1225N
RP500 Group
Step-up and Inverting
Step-up and Charge pump
Step-up and Inverting
Step-up and LDO and VD
PWM Control and VFM Control
Ricoh DC/DC converters are PWM or VFM controlled. PWM is an abbreviation for Pulse Width Modulation and VFM is an
abbreviation for Variable Frequency Modulation. (VFM is also called PFM: Pulse Frequency Modulation.)
PWM Control
The frequency is constant and the pulse width (ON time) is
changed by output load.
ON
OFF
Coil
Current
at low load at boundary condition at high load
VFM Control
The pulse width (ON time) is constant and the frequency is
changed by output load.
ON
OFF
Coil
Current
at low load at middle load at high load
Each has features as shown in below table.
DC/DC
Oscillator Frequency Pulse Width (Duty)
At Low Load
Efficiency Ripple Voltage
Noise suppression ∗
VFM Control Change Constant Good High Difficult
PWM Control Constant Change Not Good Low Easy
∗) Noise suppression: The VFM control type changes its oscillator frequency depending on the output load. Since the noise varies
according to the oscillator frequency, it is possible that noise suppression is difficult. Since the PWM control type has a constant
oscillator frequency not varying according to the output load, as a result the noise is also constant and it is easier to take
measures to reduce noise.
For optimal use, some products may switch between the two control types. The switching methods include manual switching by
means of a MODE pin and automatic switching based on the output load.
Efficiency (%)
RP506K Efficiency vs. Output Current
RP506K331A/B/C
RP506K331D/E/F
100
90
80
70
60
50
40
30
VIN=4.3V, PWM/VFM
20
VIN=5.0V, PWM/VFM
VIN=4.3V, forced PWM
10
VIN=5.0V, forced PWM
0
1 10 100 1000 10000
Output Current IOUT (mA)
Efficiency (%)
100
90
80
70
60
50
40
30
VIN=4.3V, PWM/VFM
20
VIN=5.0V, PWM/VFM
VIN=4.3V, forced PWM
10
VIN=5.0V, forced PWM
0
1 10 100 1000 10000
Output Current IOUT (mA)
123

A p p l i c a t i o n N o t e
Internal or External Output Driver Transistor
Ricoh has DC/DC converter types available with an internal output transistor and external output transistor. In internal types have
an Lx pin and are called DC/DC converters, the external types have an EXT pin and are called DC/DC controllers. (If a specific
product has both types available it is listed as a DC/DC converter)
When using an external output transistor, select a power MOSFET. When efficiency at high loads is important select a MOSFET
with a low ON resistance, but when efficiency at a low loads is more important select a MOSFET with small gate capacity. Please
use a MOSFET that has a maximum drain current higher than the maximum coil current (ILmax).
RP505Kxx1A/B
R1224Nxx2E/F/G/H/L/M
(Internal output transistor type)
(External output transistor type)
PVIN
AVIN
Ramp
Compensation
Thermal
UVLO
Shutdown
Current
Feedback
Current
Detector
LX
VIN
5
OSC
3
VOUT
MODE
CE
Soft Start Vref
Chip
Enable
Mode
Control
Switching
Control
OSC
PGND
VOUT
EXT
4
PWM/VFM
CONTROL
-
+
Protection
Amp
-
+
Vref
Soft Start
Chip Enable
1
CE
UVLO
+
-
Vref
AGND
2
GND
Products With Internal Output Transistor
RN5RK R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1210N
R1213K R1218x R1232D R1240x R1242S R1243x R1244N R1245x R1283K R1286K
R1290K R1293K R5220x RP400x RP401x RP500x RP501K RP502x RP503x RP504x
RP505K RP506K RP550K RP600K RP901K RP904Z
Products With External Output Transistor
RN5RK R1210N R1211x R1212D R1215D R1224N R1225N
The Output Voltage Setting
Ricoh has DC/DC converters types in which the output voltage is fixed internally and types that allow the output voltage to be set
with external resistors. The internal types have a VOUT pin and the external types have a VFB pin. When using an externally
adjustable type, please select proper components regarding to phase compensation and intrusion of noise.
RP505Kxx1A/B
RP505K001C
(Internally fixed output voltage type)
(Externally adjustable output voltage type)
VIN
CIN
4.7μF
PVIN
CE
LX
AVIN VOUT
RP505K
Series
AGND
L
2.2μH
VOUT
COUT
10μF
VIN
CIN
4.7μF
PVIN
CE
LX
AVIN VFB
RP505K
Series
AGND
L
2.2μH
R1
R2
C1
VOUT
COUT
10μF
DC/DC
MODE
PGND
MODE
PGND
Products With Internally Fixed Output Voltage
RN5RK R1210N R1224N R1225N R1232D R1286K R5220x RP400x RP401x RP500x
RP501K RP502x RP503x RP504x RP505K RP506K RP600K RP901K RP904Z
Products With Externally Adjustable Output Voltage
R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D
R1213K R1215D R1218x R1224N R1232D R1240x R1242S R1243x R1244N R1245x
R1283K R1286K R1290K R1293K RP400K RP401K RP505K RP506K RP550K RP600K
Application Note
124

Application Note
The Diode Rectifier and The Synchronous Rectifier
Ricoh step-down DC/DC converters can be classified into diode rectifier type and synchronous rectifier type. The diode rectifier
type is uses a schottky diode, and the synchronous rectifier type uses a low side MOS transistor. In most cases, Ricoh's
synchronous rectifier type DC/DC converters have built-in high side and low side MOS transistors except for the R1242S.
R1240x
RP500x
(Diode rectifier type)
(Synchronous rectifier type)
CSPD
470pF
R1
3.75kΩ
R2
1.2kΩ
VIN
CIN
10μF
VIN BST
R1240x
VFB
LX
GND CE
VOUT=3.3V
CBST
100nF
L4.7μH
"H"active
COUT
10μF
VIN
CIN
10μF
VIN
CE
AGND
LX
VOUT
PGND
4.7μH
VOUT
COUT
10μF
Diode Rectifier Type Step-down DC/DC Converters
R1224N R1225N R1240x R1243x R1244N R1245x R1283K R1290K R1293K
Synchronous Rectifier Type Step-down DC/DC Converters
R1232D R1242S R1286K R5220x RP500x RP501K RP502x RP503x RP504x RP505K
RP506K RP550K RP901K RP904Z
The Under Voltage Lock Out Function (UVLO)
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 circuits in the standby state until the DC/DC converter input voltage (VIN) reaches the
UVLO released voltage, it is to avoid malfunctioning of the product below the UVLO voltage. In case the input voltage (VIN) drops
below the UVLO detect voltage during operation, the UVLO function forces the DC/DC converter into the standby state to prevent
to a malfunctioning. When the input voltage (VIN) rises above the UVLO released voltage again, the UVLO released the DC/DC
converter.
Products With Under Voltage Lockout Function
R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D
R1213K R1215D R1218x R1224N R1225N R1232D R1240x R1242S R1243x R1244N
R1245x R1283K R1286K R1290K R1293K R5220x RP500x RP501K RP502x RP503x
RP504x RP505K RP506K RP550K RP901K RP904Z
DC/DC
The Soft Start Function
The Soft Start function is initiated when the input voltage
(VIN) reaches the minimum operating voltage and UVLO
voltage after power on, it is to prevent that the DC/DC
converter will cause a large inrush current and
overshoots of output voltage. The DC/DC converter is
made to start up in a smooth manner by provision of a
start up time (soft start time). There are products with an
internally fixed soft start time and products with
externally adjustable soft start time setting pin, and
products externally adjustable with an oscillator
maximum duty cycle (to be explained later).
Voltage
Graphical view of Soft Start functions
Without Soft Start function
With Soft Start function
Voltage
Time
Time
Products With Soft Start Function
R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D
R1213K R1215D R1224N R1225N R1232D R1240x R1242S R1243x R1244N R1245x
R1283K R1286K R1290K R1293K R5220x RP400x RP401x RP500x RP501K RP502x
RP503x RP504x RP505K RP506K RP550K RP600K RP901K RP904Z
125

A p p l i c a t i o n N o t e
The Oscillator Maximum Duty Cycle Externally Setting
Some products support a maximum oscillator duty cycle (Maxduty) setting by an external resistor connected to the DTC pin. The
Maxduty value is large in case the DTC pin voltage is large and vice versa, the Maxduty cycle value is small when DTC pin voltage
is small.
The soft start function is created by an external capacitor connected to the DTC pin, during start-up the DTC pin voltage is
gradually increasing. The soft start initiates from a Maxduty value of 0% and the output voltage ramps up gradually, preventing an
inrush current. The soft start time can be adjusted by the capacitance of the capacitor.
R1215D
L
SD
R3
C1
C2
C6
8
4
2
6
VIN
DELAY
EXT
VFB
GND AMPOUT
VREFOUT DTC
1
5
7
3
C5
NMOS
R4
C4
R1
R2
C3
LOAD
R5 R6 C7
Products With Externally Settable Oscillator Maximum Duty Cycle
R1212D R1215D R1290K R1293K
The Phase Compensation Externally Setting
The phase compensation of some DC/DC converters can be set with external components. Please set the phase compensation of
such products by connecting an external capacitor (speed up capacitor) and resistor to the AMPOUT pin.
The response of the products with internal phase compensation may not be optimal in some operating conditions, because the
phase compensation settings of these products give priority to the stability of the circuit in all conditions. There are guidelines
available for selecting the external parts (inductor and output capacitor). The response and the stability of the products with
external phase compensation should be best during actual operating conditions such as input voltage, output voltage, output
current, inductor, output capacitor and oscillator frequency.
In addition, please select the capacitor and the resistor used for external phase compensation based on the recommended value
and formula which is described in the product specification and carefully adjust by evaluation during operating conditions.
L
R1215D
SD
DC/DC
R3
C1
C2
C6
8
4
2
6
VIN
DELAY
EXT
VFB
GND AMPOUT
VREFOUT DTC
1
5
7
3
C5
NMOS
R4
C4
R1
R2
C3
LOAD
R5 R6 C7
Products Supporting External Phase Compensation
R1211x R1212D R1213K R1215D R1290K R1293K
Application Note
126

Application Note
The Over Voltage Protection Circuit (OVP)
The OVP circuit monitors the VOUT pin voltage and halts
oscillation once it reaches the OVP detect voltage.
Oscillation resumes when the VOUT pin voltage
decreases below the threshold again. In case the cause
of the excess VOUT pin voltage is not removed the OVP
circuit will stop and resume repeatedly in order limit the
VOUT pin voltage.
Products Supporting Over Voltage Protection (OVP)
R1205N823B OVP Operation Output Voltage Waveform
(OVP detect voltage: Typ. 25.0V, OVP release voltage: Typ. 23.2V)
Output Voltage VOUT (V)
27
26
25
24
23
22
21
0 10 20 30 40 50
Time t (ms)
R1200x R1201N R1202x R1204x R1205x R1206N R1207N R1218x
Protection Circuits (Latch Type/Reset Type/Fold back Type)
Operation of over current protection by circuit type
There are three kinds of current limit protection circuits used
in Ricoh DC/DC converters, Latch type, Reset type and Fold
back type.
• A Latch type protection circuit latches the power MOSFET
Latch Type
Over Current
Over Current Cancelation
to the OFF state during an excessive high load in case it
persists for a specified time (the protection delay time).
The circuit can be released by changing the IC into the
standby mode and back to the active mode by the CE pin,
or by turning the power off and back on. There are some
products which an adjustable protection delay time by a
capacitor connected to the DLY pin (DELAY pin).
• A Reset type protection circuit controls the power
MOSFET to the OFF state during an excessive high load
in case it persists for a specified time (the protection delay
time). The circuit is automatically released after removal
VOUT
Reset Type
VOUT
Fold back Type
Auto-release
Auto-release
Protection Delay Time
Latch Protection
Soft Start
Normal Operation
t
restart by CE signal
Protection Delay Time
Reset Protection
Soft Start
Normal Operation
t
DC/DC
of the excessive load and by triggering the soft start
operation. The protection delay time is fixed within the IC.
• A Fold back type protection circuit decreases the oscillator
frequency when the output voltage decreases below the
preset value. Therefore the minimum ON duty decreases
and the inductor ripple current increases. As a result the
Preset value
VOUT
reduce frequency
t
Auto-release
Fold back Protection
Normal Operation
Soft Start
output current decreases. The protection is automatically
released after the excessive load is removed.
Products Supporting Latch Type Protection Circuit
R1211x R1212D R1213K R1215D R1225N R1232D R1240x R1242S R1243x R1245x
R5220x R1283K R1286K R1290K R1293K RP401x RP500x RP501K RP502x RP503x
RP504x RP505K RP506K RP550K RP904Z
Products Supporting Reset Type Protection Circuit
R1224N
RP901K
Products Supporting Fold Back Type Protection Circuit
R1240x R1242S R1243x R1244N R1245x
127

A p p l i c a t i o n N o t e
The Sequence Control
Start-up and shutdown sequence controls are available in R1283x, R1290K and etc, using the soft start function, output delay
function and auto discharge function. Start-up/shutdown sequence for the LCD panel and CCD sensor can be set.
Suitable sequence control for LCD panel is available.
CE
R1290K
Capacitor for setting
the output delay time
18V
-6V
12V
Gate driver
LCD panel
Source driver
(Voltage is an example)
CE input
18V
3
85%
12V
1
Output delay time Soft start time
Soft start time
0V
Output delay
2
-6V
time
Soft start time
(Control example)
Suitable sequence control for CCD sensor is available.
CE
R1283x
15V
-7.5V
CCD sensor
CE input
1
15V
Soft start time
Soft start time
CCD vertical driver
0V
2
-7.5V
(Voltage is an example)
(Control example)
Products with sequence control
R1283x R1286K R1290K RP600K RP901K
The Shutdown Function
Due to the typical step-up DC/DC converter circuit, a voltage may appear at the output of the circuit even if the driver IC is in the
standby mode. A current flows from the battery, through the inductor and diode to the output pins. In case an OLED display is
connected, it is powered constantly and it may have an impact to the lifetime of the OLED. In addition, when the input voltage is
close to the Vf voltage of a white LED, it is unable to turn these off properly.
The R120xx Series have an internal NPN transistor instead of a diode. In standby mode, the NPN transistor turns off and isolates
the current flow from input to output.
The R1213K Series is able to shutdown that controls an external P-channel MOSFET by FLAG pin.
DC/DC
VIN
LX VIN LX
VOUT
VOUT
CE
CE
OFF
VFB
VFB
GND
R1218x
GND
R1200x
Products Containing Shutdown Function
R1200x R1202x R1213K
Application Note
128

Application Note
The LED High-speed Dimming Control
The LED brightness is set by the current through the LEDs, it can be controlled
by the Duty of a PWM signal applied to the CE pin. The current through the LEDs
can be calculated by the following formula.
ILED=Hduty × VFB / R1
Following product with high-speed dimming control can be used in the PWM
signal range between 200Hz to 300kHz.
When controlling the LED brightness with a PWM signal of 20kHz or less; The
variation of the inductor current might cause audible sounds, please use a PWM
signal in the high frequency area to avoid this.
Hduty
CE
VFB
R1
Products containing LED High-speed Dimming Control
R1201N R1202x R1203x R1204x R1205x R1206N R1207N
The Forced PWM Control
The general PWM control DC/DC converters may cause ringing in the Lx voltage because there is a zero current period to prevent
a reverse coil current in low load condition. However the forced PWM control DC/DC converters do not cause ringing by forcing
them into PWM control in low load condition.
Although the reverse coil current is present, the reverse current is not wasted because it flows to the output in the next cycle.
General PWM Mode
Forced PWM Mode
DC/DC
Ricoh forced PWM control DC/DC converters are able to switch automatically between PWM and VFM mode. If one prefers that
the supply current and efficiency are most important, please select automatic PWM/VFM switching mode. In that case the DC/DC
converter operates in VFM mode during low load conditions. If one prefers that no ringing in low load condition should appear and
operation with a constant frequency, please select fixed forced PWM control mode.
The Forced PWM Control Products
RP504x RP505K RP506K RP550K
129