Download Application Notes for DC/DC Converters

Application Notes for DC/DC Converters
Introduction
Ricoh offers a wide variety of product lineup corresponding to different output characteristics such as low input voltage to high input
voltage and small output current to large output current. Our portfolio of DC/DC converters includes step-up, step-down and
inverting DC/DC converters that are all manufactured by CMOS technology to ensure high voltage accuracy and high efficiency.
40V
High voltage
R124x Series
R127x Series
20V
Middle voltage
R1224N
R1225N
For Display panel
For white LED Backlight
PMOLED
Step-up for General Use
Step-up and Inverting
Step-up and Charge pump
Step-up, VR and Amplifier
6V
Low voltage
RP50x Series
Step-up for
General Use
Step-up and inverting
Step-up, VR and VD
Step-up/down
Step-down
Step-up
Multipul Outputs
PWM Control and VFM Control
Ricoh’s DC/DC converters are pulse-width modulation (PWM) controlled or variable-frequency modulation (VFM) controlled. VFM
is also called pulse-frequency modulation (PFM).
PWM Control
The oscillator frequency is constant and the pulse width (ON
time) changes according to the amount of output load.
at low load
at boundary condition
VFM Control
The pulse width (ON time) is constant and the oscillator
frequency changes according to the amount of output load.
at low load
at high load
ON
ON
OFF
OFF
Coil
Current
Coil
Current
at middle load
The features of VFM control and PWM control are as described below.
Oscillator Frequency
Pulse Width (Duty)
VFM Control
Change
PWM Control
Constant
∗1
Light Load Condition
Noise Suppression∗1
Efficiency
Ripple Voltage
Constant
Good
High
Difficult
Change
Not Good
Low
Easy
Noise suppression of VFM control can be difficult because oscillator frequency is inconsistent and it affects noise level.
Noise suppression of PWM control is relatively easier because oscillator frequency is constant and it does not affect noise level.
Ricoh’s DC/DC converters include the products that are only operated by PWM control and the products that can be automatically
switched between PWM mode and VFM mode according to the load condition.
1
DC/DC Converter
100
90
80
70
60
50
40
30
20
10
0
VIN=4.3V, PWM/VFM
VIN=5.0V, PWM/VFM
VIN=4.3V, forced PWM
VIN=5.0V, forced PWM
1
10
100
1000
Output Current IOUT (mA)
10000
Efficiency η (%)
Efficiency η (%)
RP506K Efficiency vs. Output Current
RP506K331A/B/C
RP506K331D/E/F
100
90
80
70
60
50
40
30
20
10
0
VIN=4.3V, PWM/VFM
VIN=5.0V, PWM/VFM
VIN=4.3V, forced PWM
VIN=5.0V, forced PWM
1
10
100
1000
Output Current IOUT (mA)
10000
DC/DC Converter
Internal or External Output Transistors
Ricoh’s DC/DC converters are equipped with internal or external output transistors. The device equipped with an internal output
transistor and the LX pin is classified as DC/DC converter. The device equipped with an external output transistor and the EXT pin
is classified as DC/DC controller. The device equipped with both internal and external output transistors is listed along with the
DC/DC converters.
A power MOSFET should be used with the external output transistor type. To achieve high efficiency under heavy load, a MOSFET
with a low ON resistance should be used. To achieve high efficiency under light load, a MOSFET with a small gate capacity should
be used. As for MOSFETs, the maximum drain current should be higher than the maximum inductor current.
RP505Kxx1A/B
R1224Nxx2E/F/G/H/L/M
(Internal Output Transistor Type)
(External Output Transistor Type)
PVIN
Ramp
Compensation
AVIN
Current
Feedback
Thermal
Shutdown
UVLO
VIN
5
EXT
4
-
Amp
+
+
Mode
Control
MODE
CE
3
VOUT
1
CE
LX
Switching
Control
Vref
Soft Start
OSC
Current
Detector
Vref
PGND
OSC
PWM/VFM
CONTROL
Chip
Enable
Soft Start
VOUT
Chip Enable
Protection
+
UVLO
Vref
-
AGND
2
GND
Internal Output Transistor Type
RN5RK
R1200x
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1208K
R1210N
R1213K
R1214Z
R1218N
R1232D
R1240x
R1242S
R1243x
R1244N
R1245x
R1270S
R1283K
RP502x
R1286K
R1287x
R1290K
R1293K
R5220K
RP400x
RP401x
RP402x
RP500x
RP501K
RP503x
RP504x
RP505K
RP506K
RP507K
RP508K
RP550K
RP600K
RP601Z
RP901K
R1212D
R1215D
R1223N
R1224N
R1225N
External Output Transistor Type
RN5RK
R1210N
R1211x
Output Voltage Setting
Ricoh’s DC/DC converters have the output voltage types that are internally fixed or externally adjustable. The internally fixed output
voltage type has the VOUT pin and the externally adjustable output voltage type has the VFB pin. Please pay attention to phase
compensation and noise sneaking when selecting the components for the externally adjustable output voltage type.
RP505Kxx1A/B
RP505K001C
(Internally Fixed Output Voltage Type)
(Externally Adjustable Output Voltage Type)
VIN
PVIN
VOUT
LX
L
2.2μH
CIN
4.7μF
AVIN
VOUT
RP505K
Series
COUT
10μF
VIN
PVIN
VOUT
LX
L
2.2μH
CIN
4.7μF
R1
VFB
AVIN
RP505K
Series
CE
AGND
CE
AGND
MODE
PGND
MODE
PGND
R2
C1
COUT
10μF
Internally Fixed Output Voltage Type
RN5RK
R1210N
R1223N
R1224N
R1225N
R1232D
R1286K
R1287x
R5220K
RP400x
RP401x
RP500x
RP501K
RP502x
RP503x
RP504x
RP505K
RP506K
RP508K
RP600K
RP601Z
RP901K
RP402x
Externally Adjustable Output Voltage Type
R1200x
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1208K
R1211x
R1212D
R1213K
R1214Z
R1215D
R1218N
R1224N
R1232D
R1240x
R1242S
R1243x
R1244N
R1245x
R1270S
R1283K
R1286K
R1287x
R1290K
R1293K
RP400K
RP401K
RP402x
RP505K
RP506K
RP507K
RP550K
RP600K
DC/DC Converter 2
Diode Rectifier and Synchronous Rectifier
Ricoh’s step-down DC/DC converters use diode rectifier and synchronous rectifier. The diode rectifier type uses a schottky diode and
the synchronous rectifier type uses a MOS transistor in the low-side switches. The high-side and low-side MOS transistors are built in
most of the Rich’s DC/DC converters except for the R1242S, which uses synchronous rectifier and an external low-side MOS transistor.
R1
3.75kΩ
CSPD
470pF
R1240x
RP500x
(Diode Rectifier Type)
(Synchronous Rectifier Type)
VOUT=3.3V
VIN
CIN
10μF
VIN
BST
VIN
CBST
100nF
L4.7μH
R1240x
VFB
CE
COUT
10μF
GND
CE
VOUT
LX
4.7μH
CIN
10μF
LX
R2
1.2kΩ
VIN
AGND
COUT
10μF
VOUT
PGND
"H"active
Diode Rectifier Type
R1224N
R1225N
R1240x
R1243x
R1244N
R1245x
R1270S
R1283K
R1290K
R1293K
RP502x
RP503x
RP504x
Synchronous Rectifier Type
R1232D
R1242S
R1286K
R1287x
R5220x
RP500x
RP501K
RP505K
RP506K
RP507K
RP508K
RP550K
RP601Z
RP901K
Undervoltage Lockout (UVLO) Function
To provide more stable operation some DC/DC converters contain a UVLO (Undervoltage Lockout) 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.
UVLO Function Included
R1200x
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1211x
R1212D
R1213K
R1214Z
R1215D
R1218N
R1224N
R1225N
R1232D
R1240x
R1242S
R1243x
R1244N
R1245x
R1270S
R1283K
R1286K
R1287x
R1290K
R1293K
R5220K
RP500x
RP501K
RP502x
RP503x
RP504x
RP505K
RP506K
RP507K
RP508K
RP550K
RP901K
RP601Z
Soft-Start Function
The Soft-start function is initiated when the input voltage
(VIN) reaches the minimum operating voltage and UVLO
With Soft Start function
Voltage
Without Soft Start function
Voltage
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).
Graphical view of Soft Start functions
Time
Time
Soft-start Function Included
3
R1200x
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1211x
R1213K
R1214Z
R1215D
R1223N
R1224N
R1225N
R1232D
R1240x
R1242S
R1243x
R1244N
R1245x
R1270S
R1283K
R1286K
R1287X
R1290K
R1293K
R5220K
RP400x
RP401x
RP402x
RP500x
RP501K
RP502x
RP503x
RP504x
RP505K
RP506K
RP550K
RP600K
RP901K
DC/DC Converter
R1212D
DC/DC Converter
Externally Programmable Maximum Duty Cycle
Some products support a maximum 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 the 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
C1
8 VIN
EXT 1
4 DELAY
VFB 5
NMOS
C4
R1
C3
C2
LOAD
R3
R2
2 GND AMPOUT 7
C5
C6
6 VREFOUT
R4
DTC 3
R5
R6
C7
Externally Programmable Maximum Duty Cycle Available
R1212D
R1215D
R1290K
R1293K
Externally Adjustable Phase Compensation
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.
R1215D
SD
L
C1
8 VIN
EXT 1
4 DELAY
VFB 5
NMOS
C4
R1
C3
C2
LOAD
R3
R2
2 GND AMPOUT 7
C5
C6
6 VREFOUT
R4
DTC 3
R5
R6
C7
Externally Adjustable Phase Compensation Available
R1211x
R1212D
R1213K
R1215D
R1290K
R1293K
DC/DC Converter 4
Overvoltage Protection (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.
R1205N823B OVP Operation Output Voltage Waveform
(OVP Detect Voltage: Typ. 25.0 V, OVP Release Voltage: Typ. 23.2 V)
Output Voltage VOUT (V)
27
26
25
24
23
22
21
0
10
20
30
Time t (ms)
40
50
Overvoltage Protection (OVP) Included
R1200x
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1208K
R1214Z
R1218N
Overcurrent Protection
There are three types of overcurrent protections that are used in Ricoh’s DC/DC converters: Latch type protection, Reset type
protection, or Hiccup type protection, and Foldback type protection.
Latch Type Protection latches 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
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).
Reset Type Protection, or Hiccup Type Protection
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 of the excessive load and by
triggering the soft start operation. The protection delay time
is fixed within the IC.
Foldback Type Protection 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
output current decreases. The protection is automatically
released after the excessive load is removed.
Latch Type
Over Current Cancelation
Over Current
Protection Delay Time
Latch Protection
VOUT
Soft Start
Normal Operation
t
Reset Type
or Hiccup Type
restart by CE signal
Protection Delay Time
Reset Protection
V OUT
Soft Start
Normal Operation
t
Auto-release
Auto-release
Fold back Type
Fold back Protection
Preset value
Normal Operation
VOUT
Soft Start
t
Auto-release
reduce frequency
Latch Type Protection Included
R1211x
R1212D
R1213K
R1215D
R1223N
R1225N
R1232D
R1240x
R1242S
R1243x
R1245x
R1270S
R1283K
R1286K
R1287x
R1290K
R1293K
R5220K
RP401x
RP402x
RP500x
RP501K
RP502x
RP503x
RP504x
RP505K
RP506K
RP550K
R1245x
R1270S
Reset Type, or Hiccup Type Protection Included
R1223N
R1224N
RP901K
Foldback Type Protection Included
R1240x
5
R1242S
DC/DC Converter
R1243x
R1244N
DC/DC Converter
Sequence Control
Start-up and shutdown sequence controls are available in R1283K, 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
CE input
Gate driver
18V
CE
R1290K
-6V
18V
3.
LCD panel
1.
Soft start time
Source driver
Output delay time
Soft start time
0V
-6V
2.
Output delay
time
Soft start time
12V
Capacitor for setting
the output delay time
12V
85%
(Voltage is an example)
(Control example)
Suitable Sequence Control for CCD Sensor
15V
CE input
CE
15V
CCD sensor
R1283x
1.
-7.5V
Soft start time
Soft start time
0V
2.
CCD vertical driver
-7.5V
(Control example)
(Voltage is an example)
Sequence Control Available
R1283K
R1286K
R1287x
R1290K
RP600K
RP901K
Shutdown Function
Generally, the input and output of the step-up DC/DC converter using diode rectifier are connected through an inductor and a
diode, as shown in the RP401x. Therefore, the device outputs the voltage almost equal to the power supply voltage even during
standby mode. To reduce the output voltage to zero, it is necessary to add FETs to shut down the input voltage. However, Ricoh’s
step-up DC/DC converter, as shown in the RP402x, uses a built-in FET instead of using a diode to enable shutdown function.
LX
VIN
LX
CE
VOUT
VOUT
CE
GND
OFF
SWITCHING
CONTROLLER
GND
RP401x
RP402x
The R1200x/ R1202x use built-in NPN transistors instead of using diodes to enable shutdown function.
The R1213K uses an external Pch MOSFET controlled by the FLAG pin to enable shutdown function.
Shutdown Function Included
R1200x
R1202x
R1213K
RP402x
DC/DC Converter 6
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.
CE
ILED = Hduty x VFB / R1
Hduty
VFB
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.
R1
LED High-speed Dimming Control Available
R1201N
R1202x
R1203x
R1204x
R1205x
R1206N
R1207N
R1208K
R1214Z
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
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.
Forced PWM Control Available
RP402x
7
RP504x
DC/DC Converter
RP505K
RP506K
RP508K
RP550K
RP601Z
1. The products and the product specifications described in this document are subject to change or
discontinuation of production without notice for reasons such as improvement. Therefore, before
deciding to use the products, please refer to Ricoh sales representatives for the latest information
thereon.
2. The materials in this document may not be copied or otherwise reproduced in whole or in part without
prior written consent of Ricoh.
3. Please be sure to take any necessary formalities under relevant laws or regulations before exporting or
otherwise taking out of your country the products or the technical information described herein.
4. The technical information described in this document shows typical characteristics of and example
application circuits for the products. The release of such information is not to be construed as a
warranty of or a grant of license under Ricoh's or any third party's intellectual property rights or any
other rights.
5. The products listed in this document are intended and designed for use as general electronic
components in standard applications (office equipment, telecommunication equipment, measuring
instruments, consumer electronic products, amusement equipment etc.). Those customers intending to
use a product in an application requiring extreme quality and reliability, for example, in a highly specific
application where the failure or misoperation of the product could result in human injury or death
(aircraft, spacevehicle, nuclear reactor control system, traffic control system, automotive and
transportation equipment, combustion equipment, safety devices, life support system etc.) should first
contact us.
6. We are making our continuous effort to improve the quality and reliability of our products, but
semiconductor products are likely to fail with certain probability. In order to prevent any injury to
persons or damages to property resulting from such failure, customers should be careful enough to
incorporate safety measures in their design, such as redundancy feature, fire containment feature and
fail-safe feature. We do not assume any liability or responsibility for any loss or damage arising from
misuse or inappropriate use of the products.
7. Anti-radiation design is not implemented in the products described in this document.
8. Please contact Ricoh sales representatives should you have any questions or comments concerning
the products or the technical information.
Halogen Free
Ricoh is committed to reducing the environmental loading materials in electrical devices
with a view to contributing to the protection of human health and the environment.
Ricoh has been providing RoHS compliant products since April 1, 2006 and Halogen-free products since
April 1, 2012.
http://www.e-devices.ricoh.co.jp/en/
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