Ricoh Power Supply RH5RH12B User Guide

PWM STEP-UP DC/DC CONVERTER  
RH5RH××1A/××2B/××3B SERIES  
APPLICATION MANUAL  
ELECTRONIC DEVICES DIVISION  
NO.EA-023-9803  
 
RH5RH SERIES  
APPLICATION MANUAL  
CONTENTS  
......................................................................................................  
OUTLINE  
1
1
1
2
2
3
3
....................................................................................................  
FEATURES  
.............................................................................................  
APPLICATIONS  
BLOCK DIAGRAM  
SELECTION GUIDE  
PIN CONFIGURATION  
.........................................................................................  
.......................................................................................  
...................................................................................  
........................................................................................  
PIN DESCRIPTION  
...................................................................  
...................................................................  
ABSOLUTE MAXIMUM RATINGS  
ELECTRICAL CHARACTERITICS  
OPERATION OF STEP-UP DC/DC CONVERTER  
4
5
...........................................  
10  
13  
13  
14  
15  
15  
16  
17  
18  
18  
18  
18  
18  
18  
19  
19  
20  
20  
20  
21  
22  
22  
......................................................................  
TYPICAL CHARACTERISTICS  
1) Output Voltage vs. Output Current .......................................................................  
2) Efficiency vs. Output Current.............................................................................  
3) Supply Current (No Load) vs. Input Voltage ..............................................................  
4) Output Current vs. Ripple Voltage........................................................................  
5) Start-up/Hold-on Voltage vs. Output Current (Topt=25˚C) ...............................................  
6) Output Voltage vs. Temperature .........................................................................  
7) Start-up Voltage vs. Temperature ........................................................................  
8) Hold-on Voltage vs. Temperature ........................................................................  
9) Supply Current 1 vs. Temperature .......................................................................  
10) Supply Current 2 vs. Temperature .......................................................................  
11) Lx Switching Current vs. Temperature ...................................................................  
12) Lx Leakage Current vs. Temperature ....................................................................  
13) Oscillator Frequency vs. Temperature....................................................................  
14) Oscillator Duty Cycle vs. Temperature ...................................................................  
15) Vlx Voltage Limit vs. Temperature........................................................................  
16) EXT “H” Output Current vs. Temperature ................................................................  
17) EXT “L” Output Current vs. Temperature.................................................................  
18) Load Transient Response ................................................................................  
19) Distribution of Output Voltage ............................................................................  
20) Distribution of Oscillator Frequency ......................................................................  
 
............................................................................  
TYPICAL APPLICATIONS  
23  
23  
23  
24  
22  
26  
26  
26  
27  
28  
28  
• RH5RH××1A .................................................................................................  
• RH5RH××2B..................................................................................................  
• RH5RH××3B..................................................................................................  
• CE pin Drive Circuit............................................................................................  
.............................................................................  
APPLICATION CIRCUITS  
• 12V Step-up Circuit............................................................................................  
• Step-down Circuit..............................................................................................  
• Step-up/Step-down Circuit with Flyback .......................................................................  
..............................................................................  
PACKAGE DIMENSIONS  
TAPING SPECIFICATIONS  
...........................................................................  
 
PWM STEP-UP DC/DC CONVERTER  
RH5RH××1A/××2B/××3B SERIES  
OUTLINE  
The RH5RH××1A/××2B/××3B Series are PWM Step-up DC/DC converter ICs by CMOS process.  
The RH5RH××1A IC consists of an oscillator, a PWM control circuit, a driver transistor (Lx switch), a refer-  
ence voltage unit, an error amplifier, a phase compensation circuit, resistors for voltage detection, a soft-start cir-  
cuit, and an Lx switch protection circuit. A low ripple, high efficiency step-up DC/DC converter can be constructed  
of this RH5RH××1A IC with only three external components, that is, an inductor, a diode and a capacitor.  
These RH5RH××1A/××2B/××3B ICs can achieve ultra-low supply current (no load) –TYP. 15µA –by a new-  
ly developed PWM control circuit, equivalent to the low supply current of a VFM (chopper) Step-up DC/DC con-  
verter.  
Furthermore, these ICs can hold down the supply current to TYP. 2µA by stopping the operation of the oscil-  
lator when the input voltage > (the output voltage set value + the dropout voltage by the diode and the inductor).  
These RH5RH××1A/××2B/××3B Series ICs are recommendable to the user who desires a low ripple PWM  
DC/DC converter, but cannot adopt a conventional PWM DC/DC converter because of its too large supply current.  
The RH5RH××2B/××3B Series ICs use the same chip as that employed in the RH5RH××1A IC and are pro-  
vided with a drive pin (EXT) for an external transistor. Because of the use of the drive pin (EXT), an external  
transistor with a low saturation voltage can be used so that a large current can be caused to flow through the  
inductor and accordingly a large output current can be obtained. Therefore, these RH5RH××2B/××3B Series ICs  
are recommendable to the user who need a current as large as several tens mA to several hundreds mA.  
The RH5RH××3B IC also includes an internal chip enable circuit so that it is possible to set the standby sup-  
ply current at MAX. 0.5µA.  
These RH5RH××1A/××2B/××3B ICs are suitable for use with battery-powered instruments with low noise  
and low supply current.  
FEATURES  
..........  
××  
Small Number of External Components  
Only an inductor, a diode and a capacitor (RH5RH 1A)  
...........................................  
Low Supply Current  
Low Ripple and Low Noise  
Low Start-up Voltage (when the output current is 1mA)  
TYP. 15µA (RH5RH301A)  
..................  
MAX. 0.9V  
..........................  
High Output Voltage Accuracy  
±2.5%  
...................................................  
High Efficiency  
TYP. 85%  
......................  
Low Temperature-Drift Coefficient of Output Voltage  
TYP. ±50 ppm/˚C  
.............................................................  
Soft-Start  
MIN. 500µs  
SOT-89 (RH5RH 1A, RH5RH 2B),  
SOT-89-5 (RH5RH  
...................................................  
××  
××  
××  
Small Packages  
3B)  
APPLICATIONS  
Power source for battery-powered equipment.  
Power source for cameras, camcorders, VCRs, PDAs, electronic data banks,and hand-held communication  
equipment.  
Power source for instruments which require low noise and low supply current, such as hand-held audio equip-  
ment.  
Power source for appliances which require higher cell voltage than that of batteries used in the appliances.  
1
 
RH5RH  
BLOCK DIAGRAM  
VLX limiter  
Buffer  
Slow start  
Vref  
Lx  
OUT  
Phase Comp.  
Vss  
LxSW  
PWM control  
+
EXT  
OSC  
Error Amp.  
Chip Enable  
CE  
Error Amp. (Error Amplifier) has a DC gain of 80dB, and Phase Comp. (Phase Compensation Circuit)  
provides the frequency characteristics including the 1st pole (fp=0.25Hz) and the zero point (fz=2.5kHz).  
Furthermore, another zero point (fz=1.0kHz) is also obtained by the resistors and a capacitor connected to  
the OUT pin.  
............  
(Note) Lx Pin  
only for RH5RH××1A and RH5RH××3B  
only for RH5RH××2B and RH5RH××3B  
only for RH5RH××3B  
.........  
EXT Pin  
...........  
CE Pin  
SELECTION GUIDE  
In RH5RH Series, the output voltage, the driver, and the taping type for the ICs can be selected at the user's  
request. The selection can be made by designating the part number as shown below :  
RH5RH×××× ×× Part Number  
a b  
c
Code  
Description  
Setting Output Voltage (VOUT):  
a
Stepwise setting with a step of 0.1V in the range of 2.7V to 7.5V is possible.  
Designation of Driver:  
1A: Internal Lx Tr. Driver (Oscillator Frequency 50kHz)  
2B: External Tr. Driver (Oscillator Frequency 100kHz)  
3B: Internal Tr./External Tr. (selectively available) (Oscillator Frequency 100kHz, with chip  
enable function)  
b
c
Designation of Taping Type :  
:
Ex. SOT-89  
T1, T2  
:
SOT-89-5 T1, T2  
(refer to Taping Specifications)  
“T1” is prescribed as a standard.  
For example, the product with Output Voltage 5.0V, the External Driver (the Oscillator Frequency 100kHz)  
and Taping Type T1, is designated by Part Number RH5RH502B-T1.  
2
 
RH5RH  
PIN CONFIGURATION  
SOT-89  
SOT-89-5  
5
4
(mark side)  
2
(mark side)  
2
1
3
1
3
PIN DESCRIPTION  
Pin No.  
Symbol  
Description  
××1B  
××2B  
××3B  
1
2
1
2
5
2
4
3
1
VSS  
OUT  
Lx  
Ground Pin  
Step-up Output Pin, Power Supply (for device itself)  
Switching Pin (Nch Open Drain)  
3
3
EXT  
CE  
External Tr. Drive Pin (CMOS Output)  
Chip Enable Pin (Active Low)  
3
 
RH5RH  
ABSOLUTE MAXIMUM RATINGS  
Vss=0V  
Symbol  
VOUT  
VLX  
Item  
Rating  
Unit  
V
Note  
Output Pin Voltage  
Lx Pin Voltage  
+12  
+12  
V
Note1  
Note2  
Note3  
VEXT  
VCE  
EXT Pin Voltage  
– 0.3 to VOUT+0.3  
V
CE Pin Voltage  
0.3 to VOUT+0.3  
V
ILX  
Lx Pin Output Current  
EXT Pin Current  
250  
mA Note1  
IEXT  
±50  
mA Note2  
PD  
Power Dissipation  
500  
30 to +80  
mW  
˚C  
Topt  
Tstg  
Tsolder  
Operating Temperature Range  
Storage Temperature Range  
Lead Temperature(Soldering)  
55 to +125  
˚C  
260˚C,10s  
(Note 1) Applicable to RH5RH××1A and RH5RH××3B.  
(Note 3) Applicable to RH5RH××3B.  
(Note 2) Applicable to RH5RH××2B and RH5RH××3B.  
ABSOLUTE MAXIMUM RATINGS  
Absolute Maximum ratings are threshold limit values that must not be exceeded even for an instant under any  
conditions. Moreover, such values for any two items must not be reached simultaneously. Operation above  
these absolute maximum ratings may cause degradation or permanent damage to the device. These are stress  
ratings only and do not necessarily imply functional operation below these limits.  
4
 
RH5RH  
ELECTRICAL CHARACTERISTICS  
• RH5RH301A  
VOUT=3.0V  
Symbol  
VOUT  
VIN  
Item  
Output Voltage  
Input Voltage  
Conditions  
MIN.  
TYP. MAX.  
Unit  
V
Note  
2.925 3.000 3.075  
8
V
Vstart  
Vhold  
Start-up Voltage  
Hold-on Voltage  
IOUT=1mA,VIN : 02V  
0.8  
0.9  
V
IOUT=1mA,VIN : 20V  
0.7  
V
To be measured at OUT Pin  
(excluding Switching Current)  
IDD1  
Supply Current 1  
15  
2
25  
5
µA  
To be measured at OUT Pin  
(excluding Switching Current)  
VIN=3.5V  
IDD2  
Supply Current 2  
µA  
ILX  
ILXleak  
fosc  
Lx Switching Current  
Lx Leakage Current  
Oscillator Frequency  
VLX=0.4V  
60  
mA  
VLX=6V,VIN=3.5V  
0.5  
60  
µA  
40  
70  
50  
80  
kHz  
Oscillator Maximum Duty  
Cycle  
Maxdty  
η
on (VLX “L” ) side  
90  
%
Efficiency  
70  
85  
%
Time required for the rising  
of VOUT up to 3V.  
tstart  
Soft-Start Time  
0.5  
2.0  
ms  
Note1  
Note2  
VLXlim  
VLX Voltage Limit  
Lx Switch ON  
0.65  
0.8  
1.0  
V
Unless otherwise provided, VIN=1.8V, VSS=0V, IOUT=10mA, Topt=25˚C, and use External Circuit of Typical  
Application (FIG. 1).  
(Note 1) Soft-Start Circuit is operated in the following sequence :  
(1) VIN is applied.  
(2) The voltage (Vref) of the reference voltage unit is maintained at 0V for about 200µs after the application of VIN.  
(3) The output of Error Amp. is raised to “H” level during the maintenance of the voltage (Vref) of the reference voltage unit.  
(4) After the rise of Vref, the output of Internal Error Amp. is gradually decreased to an appropriate value by the function of Internal Phase  
Compensation Circuit, and the Output Voltage is gradually increased in accordance with the gradual decrease of the output of Internal Error  
Amp.  
(Note 2) ILX is gradually increased after Lx Switch is turned ON. In accordance with the increase of ILX, VLX is also increased. When VLX reaches VLXlim,  
Lx Switch is turned OFF by an Lx Switch Protection Circuit.  
5
 
RH5RH  
• RH5RH501A  
VOUT=5.0V  
Symbol  
VOUT  
VIN  
Item  
Output Voltage  
Input Voltage  
Conditions  
MIN.  
TYP. MAX.  
Unit  
V
Note  
4.875 5.000 5.125  
8
V
Vstart  
Vhold  
Start-up Voltage  
Hold-on Voltage  
Iout=1mA,Vin:02V  
0.8  
0.9  
V
Iout=1mA,Vin:20V  
0.7  
V
To be measured at OUT Pin  
(excluding Switching Current)  
IDD1  
Supply Current 1  
30  
2
45  
5
µA  
µA  
To be measured at OUT Pin  
(excluding Switching Current)  
VIN=5.5V  
IDD2  
Supply Current 2  
ILX  
ILXleak  
fosc  
Lx Switching Current  
Lx Leakage Current  
Oscillator Frequency  
VLX=0.4V  
80  
mA  
µA  
VLX=6V,VIN=5.5V  
0.5  
60  
40  
70  
50  
80  
kHz  
Oscillator Maximum Duty  
Cycle  
Maxdty  
η
on (VLX “L” ) side  
90  
%
Efficiency  
70  
85  
%
Time required for the rising  
of VOUT up to 5V.  
tstart  
Soft-Start Time  
0.5  
2.0  
ms  
Note1  
Note2  
VLXlim  
VLX Voltage Limit  
Lx Switch ON  
0.65  
0.8  
1.0  
V
Unless otherwise provided, VIN=3V, Vss=0V, IOUT=10mA, Topt=25˚C, and use External Circuit of Typical  
Application (FIG. 1).  
(Note 1) Soft-Start Circuit is operated in the following sequence :  
(1) VIN is applied.  
(2) The voltage (Vref) of the reference voltage unit is maintained at 0V for about 200µs after the application of VIN.  
(3) The output of Error Amp. is raised to “H” level during the maintenance of the voltage (Vref) of the reference voltage unit.  
(4) After the rise of Vref, the output of Internal Error Amp. is gradually decreased to an appropriate value by the function of Internal Phase  
Compensation Circuit, and the Output Voltage is gradually increased in accordance with the gradual decrease of the output of Internal Error  
Amp.  
(Note 2) ILX is gradually increased after Lx Switch is turned ON. In accordance with the increase of ILX, VLX is also increased. When VLX reaches VLXlim,  
Lx Switch is turned OFF by an Lx Switch Protection Circuit.  
6
 
RH5RH  
• RH5RH302B  
Symbol  
VOUT  
VOUT=3.0V  
Item  
Conditions  
MIN.  
TYP.  
MAX.  
Unit  
V
Note  
Output Voltage  
2.925 3.000 3.075  
8
VIN  
Input Voltage  
V
Vstart  
Oscillator Start-up Voltage  
Supply Current 1  
EXT no load,VOUT :02V  
EXT no load,VOUT=2.88V  
EXT no load,VOUT=3.5V  
VEXT=VOUT–0.4V  
0.7  
30  
2
0.8  
50  
5
V
IDD  
IDD  
µA  
µA  
mA  
mA  
kHz  
1
Supply Current 2  
2
IEXTH  
IEXTL  
fosc  
EXT “H” Output Current  
EXT “L” Output Current  
Oscillator Frequency  
–1.5  
1.5  
80  
VEXT=0.4V  
100  
80  
120  
90  
Oscillator Maximum Duty  
Cycle  
Maxdty  
tstart  
VEXT “H” side  
70  
%
Time required for the rising  
of VOUT up to 3V  
Soft-Start Time  
0.5  
2.0  
ms  
Note1  
Unless otherwise provided, VIN=1.8V, Vss=0V, IOUT=10mA, Topt=25˚C, and use External Circuit of Typical  
Application (FIG. 2).  
VOUT=5.0V  
• RH5RH502B  
Symbol  
VOUT  
VIN  
Item  
Conditions  
MIN.  
TYP.  
MAX.  
Unit  
V
Note  
Output Voltage  
4.875 5.000 5.125  
8
Input Voltage  
V
Vstart  
Oscillator Start-up Voltage  
Supply Current 1  
EXT no load,VOUT :02V  
EXT no load,VOUT=4.8V  
EXT no load,VOUT=5.5V  
VEXT=VOUT–0.4V  
0.7  
60  
2
0.8  
90  
5
V
IDD  
IDD  
µA  
µA  
mA  
mA  
kHz  
1
Supply Current 2  
2
IEXTH  
IEXTL  
fosc  
EXT “H” Output Current  
EXT “L” Output Current  
Oscillator Frequency  
–2  
2
VEXT=0.4V  
80  
100  
80  
120  
90  
Oscillator Maximum Duty  
Cycle  
Maxdty  
VEXT “H” side  
70  
%
Time required for the rising  
of VOUT up to 5V  
start  
t
Soft-Start Time  
0.5  
2.0  
ms  
Note1  
Unless otherwise provided, VIN=3V, Vss=0V, IOUT=10mA, Topt=25˚C and use External Circuit of Typical  
Application (FIG. 2).  
(Note 1) refer to page 5 (Note 1)  
7
 
RH5RH  
• RH5RH303B  
Symbol  
VOUT=3.0V  
Item  
Output Voltage  
Input Voltage  
Start-up Voltage  
Hold-on Voltage  
Efficiency  
Conditions  
MIN.  
TYP.  
MAX.  
Unit  
V
Note  
VOUT  
VIN  
2.925 3.000 3.075  
8
V
Vstart  
Vhold  
η
IOUT=1mA,VIN : 0 2V  
0.8  
0.9  
V
IOUT=1mA,VIN : 2 0V  
0.7  
70  
V
85  
30  
%
IDD1  
Supply Current 1  
To be measured at OUT pin  
50  
5
µA  
To be measured at OUT pin  
VIN=3.5V  
2
µA  
IDD2  
Supply Current 2  
ILX  
Lx Switching Current  
Lx Leakage Current  
EXT “H” Output Current  
EXT “L” Output Current  
CE “H” Level 1  
VLX=0.4V  
VLX=6V,VIN=3.5V  
VEXT=VOUT–0.4V  
VEXT=0.4V  
60  
mA  
µA  
mA  
mA  
V
0.5  
ILXleak  
IEXTH  
IEXTL  
VCEH1  
VCEL1  
VCEH2  
VCEL2  
ICEH  
–1.5  
1.5  
VOUT1.5V  
V
OUT0.4  
CE “L” Level 1  
VOUT1.5V  
0.4  
V
CE “H” Level 2  
0.8VVOUT<1.5V  
0.8VVOUT<1.5V  
CE=3V  
V
OUT–0.1  
V
CE “L” Level 2  
0.1  
0.5  
V
CE “H” Input Current  
CE “L” Input Current  
Oscillator Frequency  
µA  
µA  
kHz  
ICEL  
CE=0V  
–0.5  
80  
fosc  
100  
80  
120  
90  
Oscillator Maximum Duty  
Cycle  
Maxdty  
on (VLX “L” )side  
70  
%
Time required for the rising  
of VOUT up to 3V.  
0.5  
2.0  
0.8  
ms  
V
Note1  
Note2  
tstart  
Soft-Start Time  
VLXlim  
VLX Voltage Limit  
Lx Switch ON  
0.65  
1.0  
Unless otherwise provided, VIN=1.8V, VSS=0V, IOUT=10mA, Topt=25˚C, and use External Circuit of Typical  
Application (FIG. 3).  
(Note 1) Soft-Start Circuit is operated in the following sequence :  
(1) VIN is applied.  
(2) The voltage (Vref) of the reference voltage unit is maintained at 0V for about 200µs after the application of VIN.  
(3) The output of Error Amp. is raised to “H” level during the maintenance of the voltage (Vref) of the reference voltage unit.  
(4) After the rise of Vref, the output of Internal Error Amp. is gradually decreased to an appropriate value by the function of Internal Phase Com  
pensation Circuit, and the Output Voltage is gradually increased in accordance with the gradual decrease of the output of Internal Error Amp.  
(Note 2) ILX is gradually increased after Lx Switch is turned ON. In accordance with the increase of ILX, VLX is also increased. When VLX reaches VLXlim,  
Lx Switch is turned OFF by an Lx Switch Protection Circuit.  
8
 
RH5RH  
• RH5RH503B  
Symbol  
VOUT=5.0V  
Item  
Output Voltage  
Input Voltage  
Start-up Voltage  
Hold-on Voltage  
Efficiency  
Conditions  
MIN.  
TYP.  
MAX.  
Unit  
V
Note  
VOUT  
VIN  
4.875 5.000 5.125  
8
V
Vstart  
Vhold  
η
IOUT=1mA,VIN : 0 2V  
0.8  
0.9  
V
IOUT=1mA,VIN : 2 0V  
0.7  
70  
V
85  
60  
%
IDD1  
Supply Current 1  
To be measured at OUT pin  
90  
5
µA  
To be measured at OUT pin  
VIN=5.5V  
2
µA  
IDD2  
Supply Current 2  
ILX  
Lx Switching Current  
Lx Leakage Current  
EXT “H” Output Current  
EXT “L” Output Current  
CE “H” Level 1  
VLX=0.4V  
VLX=6V,VIN=5.5V  
VEXT=VOUT–0.4V  
VEXT=0.4V  
80  
mA  
µA  
mA  
mA  
V
0.5  
ILXleak  
IEXTH  
IEXTL  
VCEH1  
VCEL1  
VCEH2  
VCEL2  
ICEH  
–2.0  
2.0  
VOUT1.5V  
V
OUT0.4  
CE “L” Level 1  
VOUT1.5V  
0.4  
V
CE “H” Level 2  
0.8VVOUT<1.5V  
0.8VVOUT<1.5V  
CE=5V  
V
OUT–0.1  
V
CE “L” Level 2  
0.1  
0.5  
V
CE “H” Input Current  
CE “L” Input Current  
Oscillator Frequency  
µA  
µA  
kHz  
ICEL  
CE=0V  
–0.5  
80  
fosc  
100  
80  
120  
90  
Oscillator Maximum Duty  
Cycle  
Maxdty  
on (VLX “L” )side  
70  
%
Time required for the rising  
of VOUT up to 5V.  
0.5  
2.0  
0.8  
ms  
V
Note1  
Note2  
tstart  
Soft-Start Time  
VLXlim  
VLX Voltage Limit  
Lx Switch ON  
0.65  
1.0  
Unless otherwise provided, VIN=3V, VSS=0V, IOUT=10mA, Topt=25˚C, and use External Circuit of Typical  
Application (FIG. 3).  
(Note 1) Soft-Start Circuit is operated in the following sequence :  
(1) VIN is applied.  
(2) The voltage (Vref) of the reference voltage unit is maintained at 0V for about 200µs after the application of VIN.  
(3) The output of Error Amp. is raised to “H” level during the maintenance of the voltage (Vref) of the reference voltage unit.  
(4) After the rise of Vref, the output of Internal Error Amp. is gradually decreased to an appropriate value by the function of Internal Phase Com  
pensation Circuit, and the Output Voltage is gradually increased in accordance with the gradual decrease of the output of Internal Error Amp.  
(Note 2) ILX is gradually increased after Lx Switch is turned ON. In accordance with the increase of ILX, VLX is also increased. When VLX reaches VLXlim,  
Lx Switch is turned OFF by an Lx Switch Protection Circuit.  
9
 
RH5RH  
OPERATION OF STEP-UP DC/DC CONVERTER  
Step-up DC/DC Converter charges energy in the inductor when Lx Transistor (LxTr) is on, and discharges the  
energy with the addition of the energy from Input Power Source thereto, so that a higher output voltage than the  
input voltage is obtained.  
The operation will be explained with reference to the following diagrams :  
< Basic Circuits >  
< Current through L >  
IL  
i2  
SD  
ILmax  
ILmin  
topen  
IOUT  
L
VIN  
VOUT  
i1  
t
Lx Tr  
CL  
toff  
ton  
T=1/fosc  
Step 1 : LxTr is turned ON and current IL (= i1 ) flows, so that energy is charged in L. At this moment, IL(=i1 ) is  
increased from ILmin (= 0) to reach ILmax in proportion to the on-time period (ton) of LxTr.  
Step 2 : When LxTr is turned OFF, Schottky diode (SD) is turned ON in order that L maintains IL at ILmax, so  
that current IL (= i2) is released.  
Step 3 : IL (=i2) is gradually decreased, and in the case of discontinuous mode, IL reaches ILmin (=0) after a time  
period of topen, so that SD is turned OFF. However, in the case of a continuous mode which will be mentioned  
later,the time period (toff) runs out before IL reaches ILmin (=0), so that LxTr is turned ON in the next  
cycle, and SD is turned OFF. In this case, ILmin does not reach zero, and IL (=i1) increases from ILmin (> 0).  
In the case of PWM control system, the output voltage is maintained constant by controlling the on-time peri-  
od (ton), with the oscillator frequency (fosc) being maintained constant.  
Discontinuous Conduction Mode and Continuous Conduction Mode  
In the above two diagrams, the maximum value (ILmax) and the minimum value (ILmin) of the current which  
flows through the inductor are the same as those when LxTr is ON and also when LxTr is OFF.  
The difference between ILmax and ILmin, which is represented by I, is :  
.........................................  
I=ILmax–ILmin=VIN · ton/L=(VOUT–VIN) · topen/L  
Equation 1  
wherein T=1/fosc=ton+toff  
duty (%)=ton/T · 100=ton · fosc · 100  
topentoff  
In Equation 1, VIN · ton/L and (VOUT–VIN) · topen/L are respectively show the change in the current at ON, and the  
change in the current at OFF.  
10  
 
RH5RH  
When the output current (IOUT) is relatively small, topen<toff as illustrated in the above diagram. In this case,  
the energy charged in the inductor during the time period of ton is discharged in its entirely during the time peri-  
od of toff, so that ILmin becomes zero (ILmin=0). When IOUT is gradually increased, topen eventually becomes  
equal to toff (topen=toff), and when IOUT is further increased. ILmin becomes larger than zero (ILmin>0). The  
former mode is referred to as the discontinuous mode and the latter mode is referred to as the continuous mode.  
In the continuous mode, when Equation 1 is solved for ton and the solution is tonc,  
................................................................................................  
tonc =T · (1–VIN/VOUT)  
Equation 2  
When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.  
Output Current in Discontinuous Mode  
In the discontinuous mode, when LxTr is on, the energy PON charged in the inductor is provided by Equation 3  
as follows :  
ton  
2
PON=0ton VIN · IL (t) dt =0 (VIN · t/L) dt  
2
2
.................................................................................................  
=VIN · ton /(2 · L)  
Equation 3  
In the case of the step-up DC/DC converter, the energy is also supplied from the input power source at the time  
of OFF.  
Thus, POFF=topen VIN · IL (t) dt =topen ((VOUT–VIN) · t/L)dt  
0
0
=VIN · (VOUT–VIN) · topen2/(2 · L)  
Here, topen=VIN · ton/(VOUT–VIN) from Equation 1, and when this is substituted into the above equation.  
3
2
..........................................................................  
=VIN · ton /(2 · L · (VOUT–VIN)  
Equation 4  
Input power is (PON+POFF)/T. When this is converted in its entirely to the output.  
PIN=(PON+POFF)/T=VOUT · IOUT=POUT .....................................................................  
Equation 5  
Equation 6 can be obtained as follows by solving Equation 5 for IOUT by substituting Equations 3 and 4 into  
Equation 5 :  
2
2
.....................................................................  
IOUT=VIN · ton /(2 · L · T · (VOUT–VIN))  
Equation 6  
The peak current which flows through L · LxTr · SD is  
......................................................................................................  
ILmax=VIN · ton/L  
Equation 7  
11  
 
RH5RH  
Therefore it is necessary that the setting of the input/output conditions and the selection of peripheral compo-  
nents should be made with ILmax taken into consideration.  
Output Current in Continuous Conduction Mode  
When the operation enters into the continuous conduction mode by increasing the IOUT, ILmin becomes equal  
to Iconst (> 0), and this current always flows through the inductor. Therefore, VIN · Iconst is added to PIN in  
Equation 5.  
Thus, PIN=VIN · Iconst+(PON+POFF)/T=VOUT · IOUT=POUT  
When the above Equation is solved for IOUT,  
2
2
IOUT=VIN · tonc /(2 · L · T · (VOUT–VIN))+VIN · Iconst/VOUT ............................................  
Equation 8  
Equation 9  
The peak current which flows through L · LxTr · SD is  
...................................................................................................  
ILmax=VIN · ton/L+Iconst  
From Equations 6 and 9, the larger the value of L, the smaller the load current at which the operation enters  
into the continuous mode, and the smaller the difference between ILmax and ILmin, and the smaller the value of  
ILmax.  
Therefore, when the load current is the same, the larger the value of L, the easier the selection of peripheral  
components with a small allowable current becomes, and the smaller the ripple of the peripheral components can  
be made. In this case, however, it must be noted from Equation 6 that IOUT becomes small when the allowable cur-  
rent of the inductor is small or when VIN is so small that the operation cannot enter into the continuous mode.  
HINTS  
The above explanation is directed to the calculation in an ideal case where there is no energy loss caused by the  
resistance in the external components and LxSW. In an actual case, the maximum output current will be 50  
to 80% of the above calculated maximum output current. In particular, care must be taken because VIN is  
decreased in an amount corresponding to the voltage drop caused by LxSW when IL is large or VIN is low.  
Furthermore, it is required that with respect to VOUT, Vf of the diode (about 0.3V in the case of a Schottky type  
diode) be taken into consideration.  
12  
 
RH5RH  
TYPICAL CHARACTERISTICS  
1) Output Voltage vs. Output Current  
RH5RH301A  
RH5RH301A  
L=270µH  
L=120µH  
3.1  
3.1  
3.0  
2.9  
2.8  
2.7  
2.6  
2.5  
3.0  
2.9  
2.8  
2.7  
1.5V  
2.0V  
1.5V  
2.6  
2.5  
VIN=1.0V  
20  
2.0V  
50  
VIN =1.0V  
0
10  
30  
40  
60  
0
20  
60  
40  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
RH5RH501A  
RH5RH501A  
L=120µH  
L=270µH  
5.2  
5.0  
4.8  
4.6  
4.4  
4.2  
4.0  
5.2  
5.0  
4.8  
4.6  
4.4  
4.2  
4.0  
4.0V  
3.0V  
2.0V  
3.0V  
2.0V  
50  
4.0V  
VIN=  
1.0V  
VIN=1.0V  
0
100  
150  
0
50  
100  
150  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
RH5RH302B  
RH5RH502B  
L=28µH  
2.5V  
L=28µH  
4.0V  
3.1  
5.2  
5.0  
4.8  
4.6  
4.4  
3.0V  
2.0V  
2.0V  
1.5V  
3.0  
2.9  
2.8  
VIN=0.9V  
VIN=1.5V  
0
200  
400  
600  
0
500  
1000  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
13  
 
RH5RH  
2) Efficiency vs. Output Current  
RH5RH301A  
RH5RH301A  
L=120µH  
2.0V  
L=270µH  
2.0V  
90  
100  
90  
80  
70  
60  
50  
40  
80  
70  
60  
1.5V  
VIN=1.0V  
VIN=1.0V  
1.5V  
50  
40  
0
10  
30  
20  
0
10  
20  
30  
40  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
RH5RH501A  
RH5RH501A  
L=270µH  
L=120µH  
4.0V  
100  
90  
100  
90  
80  
70  
60  
80  
70  
4.0V  
3.0V  
2.0V  
VIN=  
1.0V  
3.0V  
60  
50  
40  
VIN=1.0V  
2.0V  
50  
40  
0
50  
100  
150  
0
50  
150  
100  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
RH5RH302B  
RH5RH502B  
L=28µH  
4.0V  
L=28µH  
2.5V  
100  
100  
80  
80  
60  
40  
20  
0
3.0V  
2.0V  
2.0V  
1.5V  
60  
40  
VIN=0.9V  
VIN=1.5V  
20  
0
0
500  
1000  
200  
Output Current IOUT(mA)  
600  
0
400  
Output Current IOUT(mA)  
14  
 
RH5RH  
3) Supply Curret (No Load) vs. Input Voltage  
RH5RH301A  
RH5RH301A  
L=270µH  
L=120µH  
70  
60  
50  
40  
70  
60  
50  
40  
30  
20  
10  
0
30  
20  
10  
0
1.0  
1.2  
1.4  
1.6  
1.8  
2.0  
1.0  
1.2  
1.6  
1.8  
2.0  
1.4  
Input Voltage VIN(V)  
Input Voltage VIN(V)  
RH5RH501A  
RH5RH501A  
L=270µH  
L=120µH  
200  
200  
150  
100  
150  
100  
50  
0
50  
0
1
2
3
4
1
2
3
4
Input Voltage VIN(V)  
Input Voltage VIN(V)  
4) Output Current vs.Ripple Voltage  
RH5RH301A  
RH5RH501A  
L=120µH  
L=120µH  
100  
80  
90  
80  
70  
60  
50  
70  
60  
2.0V  
4.0V  
3.0V  
3.0V  
2.0V  
VIN=0.9V  
50  
40  
30  
20  
10  
VIN=0.9V  
40  
30  
20  
10  
0
0
50 60 70 80 90 100  
1
5
10 20 30 40  
5
50 60 70 80 90 100  
1
10 20 30 40  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
15  
 
RH5RH  
RH5RH301A  
RH5RH501A  
L=270µH  
4.0V  
L=270µH  
3.0V  
80  
70  
60  
50  
40  
70  
60  
50  
3.0V  
40  
30  
20  
10  
0
VIN=0.9V  
2.0V  
30  
20  
10  
0
2.0V  
VIN=0.9V  
1
10 20 30 40 50 60 70 80 90  
Output Current IOUT(mA)  
1
10  
20 30 40 50 60  
Output Current IOUT(mA)  
70 80  
RH5RH302B  
RH5RH502B  
L=28µH  
3.0V  
L=28µH  
70  
60  
50  
120  
100  
80  
60  
40  
20  
0
VIN=0.9V  
2.0V  
3.0V  
2.0V  
40  
30  
20  
4.0V  
VIN=0.9V  
10  
0
1
50  
100  
150  
200  
1
50  
100  
150  
200  
250  
Output Current IOUT(mA)  
Output Current IOUT(mA)  
5) Start-up/Hold-on Voltage vs. Output Current (Topt=25˚C)  
RH5RH301A  
RH5RH501A  
L=120µH  
L=120µH  
1.4  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0
1.6  
1.4  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0
Vstart  
Vstart  
Vhold  
Vhold  
0
10  
20  
Output Current IOUT(mA)  
30  
0
30  
10  
20  
Output Current IOUT(mA)  
16  
 
RH5RH  
RH5RH502B  
RH5RH302B  
L=28µH  
L=28µH  
1.4  
1.2  
1.0  
1.4  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0
Vstart  
Vhold  
Vstart  
Vhold  
0.8  
0.6  
0.4  
0.2  
0
20  
40  
60  
80  
100  
0
20  
40  
60  
80  
100  
0
Output Current IOUT(mA)  
Output Current IOUT(mA)  
6) Output Voltage vs.Temperature  
IOUT=10mA  
VIN=2V  
L=120µH  
IOUT=10mA  
VIN=3V  
L=120µH  
RH5RH301A  
RH5RH501A  
3.2  
5.2  
5.1  
5.0  
3.1  
3.0  
2.9  
2.8  
2.7  
4.9  
4.8  
4.7  
–40  
0
20  
40  
60  
80  
100  
–20  
–40  
0
20  
40  
60  
80  
–20  
100  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
IOUT=10mA  
VIN=2V  
L=28µH  
IOUT=10mA  
VIN=3V  
L=28µH  
RH5RH302B  
RH5RH502B  
3.2  
5.2  
5.1  
5.0  
4.9  
4.8  
3.1  
3.0  
2.9  
2.8  
2.7  
–40  
4.7  
–40 –20  
0
20  
40  
60  
80  
100  
–20  
0
20  
40  
60  
80  
100  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
17  
 
RH5RH  
7) Start-up Voltage vs. Temperature  
8) Hold-on Voltage vs. Temperature  
RH5RH501A  
RH5RH501A  
1.0  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0
0.8  
0.6  
0.4  
0.2  
0
–40  
–20  
0
20  
40  
60  
80  
–40 –20  
0
40  
60  
80  
20  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
9) Supply Current 1 vs.Temperature  
10) Supply Current 2 vs.Temperature  
RH5RH501A  
RH5RH501A  
100  
5
80  
60  
4
3
2
40  
20  
0
1
0
–40  
0
20  
40  
60  
80  
–20  
–40  
0
20  
40  
60  
80  
–20  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
11) Lx Switching Current vs.Temperature  
12) Lx Leakage Current vs.Temperature  
RH5RH501A  
RH5RH501A  
1.0  
150  
125  
100  
75  
50  
25  
0
0.8  
0.6  
0.4  
0.2  
0
–40  
–20  
0
20  
40  
60  
80  
–40  
0
20  
40  
60  
80  
–20  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
18  
 
RH5RH  
13) Oscillator Frequency vs. Temperature  
IOUT=10mA  
RH5RH301A  
IOUT=10mA  
RH5RH501A  
VIN=2V  
VIN=3V  
L=120µH  
L=120µH  
100  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
–40 –20  
0
20  
40  
60  
80 100  
–40 –20  
0
20  
40  
60  
80  
100  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
IOUT=10mA  
VIN=2V  
L=28µH  
RH5RH302B  
RH5RH502B  
IOUT=10mA  
VIN=3V  
L=28µH  
140  
140  
120  
100  
80  
60  
40  
20  
0
120  
100  
80  
60  
40  
20  
0
–40 –20  
0
20  
40  
60  
80  
100  
–40 –20  
0
20  
40  
60  
80  
100  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
14) Oscillator Duty Cycle vs. Temperature  
RH5RH301A  
IOUT=10mA  
VIN=2V  
L=120µH  
RH5RH501A  
IOUT=10mA  
VIN=3V  
L=120µH  
100  
90  
80  
70  
60  
50  
100  
90  
80  
70  
60  
50  
60  
80  
–40  
–20  
0
20  
40  
–40  
–20  
0
20  
40  
60  
80  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
19  
 
RH5RH  
IOUT=10mA  
VIN=2V  
L=28µH  
IOUT=10mA  
VIN=3V  
L=28µH  
RH5RH502B  
RH5RH302B  
100  
90  
100  
90  
80  
70  
60  
50  
80  
70  
60  
50  
–40  
–20  
0
20  
40  
60  
80  
–40  
–20  
0
20  
40  
60  
80  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
15) VLX Voltage Limit vs. Temperature  
RH5RH501A  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0.0  
80  
–40  
–20  
0
60  
20  
40  
Temperature Topt(˚C)  
16) EXT “H” Output Current vs. Temperature  
17) EXT “L” Output Current vs. Temperature  
RH5RH501A  
RH5RH501A  
10  
10  
8
6
4
2
8
6
4
2
0
0
–40  
–40  
–20  
0
20  
40  
60  
80  
–20  
0
20  
40  
60  
80  
Temperature Topt(˚C)  
Temperature Topt(˚C)  
20  
 
RH5RH  
18) Load Transient Response  
RH5RH301A  
IOUT=1mA-30mA  
VIN=2V  
RH5RH501A  
IOUT=1mA-30mA  
VIN=3V  
L=120µH  
L=120µH  
5.0  
4.5  
4.0  
240  
7.0  
6.5  
6.0  
5.5  
240  
210  
180  
210  
180  
150  
Output Voltage  
Output Current  
3.5  
150  
120  
90  
Output Voltage  
3.0  
2.5  
2.0  
120  
90  
60  
30  
0
5.0  
4.5  
4.0  
3.5  
60  
Output Current  
30  
0
1.5  
1.0  
3.0  
20  
40  
60  
0
80  
0
20  
40  
60  
80  
Time t(ms)  
Time t(ms)  
RH5RH302B  
RH5RH502B  
IOUT=1mA-30mA  
VIN=3V  
IOUT=1mA-30mA  
VIN=2V  
L=28µH  
L=28µH  
7.0  
240  
240  
5.0  
4.5  
4.0  
3.5  
6.5  
6.0  
5.5  
5.0  
4.5  
4.0  
3.5  
3.0  
210  
180  
210  
180  
Output Voltage  
Output Voltage  
Output Current  
150  
120  
90  
150  
120  
90  
60  
30  
0
3.0  
2.5  
60  
30  
0
2.0  
1.5  
Output Current  
1.0  
0
20  
40  
Time t(ms)  
60  
80  
0
20  
40  
60  
80  
Time t(ms)  
21  
 
RH5RH  
19) Distribution of Output Voltage  
RH5RH501A  
5.18~5.20  
5.16~5.18  
5.14~5.16  
5.12~5.14  
5.10~5.12  
5.08~5.10  
5.06~5.08  
5.04~5.06  
5.02~5.04  
5.00~5.02  
4.98~5.00  
4.96~4.98  
4.94~4.96  
4.92~4.94  
4.90~4.92  
4.88~4.90  
4.86~4.88  
4.84~4.86  
4.82~4.84  
4.80~4.82  
0
5
10  
15  
20  
25  
30  
35  
Distribution (%)  
20) Distribution of Oscillator Frequency  
RH5RH501A  
59~60  
58~59  
57~58  
56~57  
55~56  
54~55  
53~54  
52~53  
51~52  
50~51  
49~50  
48~49  
47~48  
46~47  
45~46  
44~45  
43~44  
42~43  
41~42  
40~41  
0
5
10  
15  
Distribution (%)  
20  
25  
22  
 
RH5RH  
TYPICAL APPLICATIONS  
• RH5RH××1A  
Diode  
Inductor  
VOUT  
Lx  
OUT  
Vss  
+
VIN  
Capacitor  
Components Inductor (L)  
Diode (D)  
: 120µH (Sumida Electric Co., Ltd.)  
: MA721 (Matsushita Electronics Corporation, Schottky Type)  
: 22µF (Tantalum Type)  
Capacitor (CL)  
FIG. 1  
• RH5RH××2B  
Inductor  
Diode  
VOUT  
Cb  
Rb  
OUT  
EXT  
Vss  
+
VIN  
Capacitor  
Tr  
Components Inductor (L)  
: 28µH (Troidal Core)  
Diode (D)  
: HRP22 (Hitachi, Schottky Type)  
: 100µF (Tantalum Type)  
: 2SD1628G  
Capacitor (CL)  
Transistor (Tr)  
Base Resistor (Rb)  
: 300Ω  
Base Capacitor (Cb) : 0.01µF  
FIG. 2  
23  
 
RH5RH  
RH5RH××3B  
Diode  
Inductor  
VOUT  
Lx  
OUT  
NC  
EXT  
CE Vss  
+
VIN  
Capacitor  
Components Inductor (L)  
Diode (D)  
: 120µH (Sumida Electric Co., Ltd.)  
: MA721 (Matsushita Electronics Corporation, Schottky Type)  
: 22µF (Tantalum Type)  
Capacitor (CL)  
FIG. 3  
Inductor  
Diode  
VOUT  
NC  
Lx  
Cb  
Rb  
OUT  
EXT  
CE  
Vss  
+
VIN  
Capacitor  
Tr  
Components Inductor (L)  
Diode (D)  
: 28µH (Troidal Core)  
: HRP22 (Hitachi, Schottky Type)  
: 100µF (Tantalum Type)  
: 2SD1628G  
Capacitor (CL)  
Transistor (Tr)  
Base Resistor (Rb)  
: 300Ω  
Base Capacitor (Cb) : 0.01µF  
FIG. 4  
24  
 
RH5RH  
• CE pin Drive Circuit  
Diode  
Inductor  
RH5RH××3B  
VOUT  
Lx  
OUT  
NC  
EXT  
CE  
Vss  
Pull-up  
resistor  
+
Capacitor  
VIN  
CE  
Tr  
FIG. 5  
25  
 
RH5RH  
APPLICATION CIRCUITS  
• 12V Step-up Circuit  
Inductor  
Diode  
VOUT  
ZD:6.8V  
RH5RH502B  
Cb  
Rb  
OUT  
EXT  
+
Capacitor  
VIN  
Vss  
RZD  
Tr  
Starter Circuit  
(Note) When the Output Current is small or the Output Voltage is unstable,use the Rzd for flowing the bias current through the Zener diode ZD.  
FIG. 6  
• Step-down Circuit  
Inductor  
VOUT  
PNP  
Tr  
Diode  
RH5RH××1A  
OUT  
Rb2  
Lx  
VIN  
Rb1  
+
Vss  
Capacitor  
Starter Circuit  
(Note) When the LX pin Voltage is over the rating at the time PNP Tr is OFF,use a RH5RH××2B and drive the PNP Tr. by the external NPN Tr.  
FIG. 7  
26  
 
RH5RH  
• Step-up/Step-down Circuit with Flyback  
Diode  
VOUT  
Trance1:1  
RH5RH××1A  
OUT  
Lx  
VIN  
+
Vss  
Capacitor  
Starter Circuit  
(Note) Use a RH5RH××2B,depend on the Output Current.  
FIG. 8  
The Starter Circuit is necessary for all above circuits.  
*
1.for Step-up Circuit.  
VOUT side  
VIN side  
Starter Circuit  
2.for Step-down and Step-up/Step-down Circuit.  
VIN side  
VOUT side  
Tr  
RST  
Starter Circuit  
ZDST  
ZDst 2.5V/ZDstDesignation of Output Voltage  
Rst Input Bias Current of ZDst and Tr.  
(several kto several hundreds k)  
27  
 
RH5RH  
PACKAGE DIMENSIONS (Unit: mm)  
• SOT-89  
• SOT-89-5  
4.5±0.1  
1.6±0.2  
4.5±0.1  
1.5±0.1  
1.5±0.1  
1.6±0.2  
0.4±0.1  
0.42±0.1  
0.4±0.1  
4
5
ø1.0  
ø1.0  
3
1
2
0.4±0.1  
3
1
2
0.4±0.1  
0.42  
±0.1  
0.47  
±0.1  
0.42  
±0.1  
0.42  
±0.1  
0.47  
±0.1  
0.42  
±0.1  
1.5±0.1  
1.5±0.1  
1.5±0.1  
1.5±0.1  
TAPING SPECIFICATIONS (Unit: mm)  
• SOT-89  
+0.1  
ø 1.5  
4.0±0.1  
–0  
0.3±0.1  
2.0±0.05  
5.0  
8.0±0.1  
2.5MAX.  
T 2  
T 1  
User Direction of Feed.  
• SOT-89-5  
4.0±0.1  
+0.1  
–0  
ø 1.5  
5.0  
0.3±0.1  
2.0±0.05  
4.7  
8.0±0.1  
2.5MAX.  
T 2  
T 1  
User Direction of Feed.  
28  
 
RH5RH  
APPLICATION HINTS  
When using these ICs, be sure to take care of the following points :  
Set external components as close as possible to the IC and minimize the connection between the components  
and the IC. In particular, when an external component is connected to OUT Pin, make minimum connection  
with the capacitor.  
Make sufficient grounding. A large current flows through Vss Pin by switching. When the impedance of the  
Vss connection is high, the potential within the IC is varied by the switching current. This may result in  
unstable operation of the IC.  
Use capacitor with a capacity of 10µF or more, and with good high frequency characteristics such as tanta-  
lum capacitor. We recommend the use of a capacitor with a resistance to the voltage being at least three  
times the output set voltage. This is because there may be the case where a spike-shaped high voltage is gen-  
erated by the inductor when Lx transistor is turned OFF.  
Take the utmost care when choosing a inductor. Namely, choose such an inductor that has sufficiently small  
d.c. resistance and large allowable current, and hardly reaches magnetic saturation. When the inductance  
value of the inductor is small, there may be the case where ILX exceeds the absolute maximum ratings at the  
maximum load. Use an inductor with an appropriate inductance.  
Use a diode of a Schottky type with high switching speed, and also take care of the rated current.  
These ICs are provided with a soft-start circuit. However, there may be the case where the overshoot of the  
out put voltage takes place depending upon the peripheral circuits employed and the input/output condi-  
tions. In particular, when the input voltage is increased slowly, the occurrence of the overshoot of the output  
voltage becomes conspicuous. Therefore in the case where the overshoot becomes a problem, take a counter-  
measure against this problem, for example, by clamping the output (OUT Pin) by use of a Zener diode.  
The transient response characteristics corresponding to the variations in the input and output are set so as  
to be slightly delayed by an internal phase compensation circuit in order to prevent the oscillation. because  
of such setting of the transient response characteristics, take care of the occurrence of the overshoot and/or  
undershoot of the output voltage.  
The internal phase compensation circuit is designed with the avoidance of the problem of the occurrence of  
the oscillation fully taken into consideration. However, there may be the case the oscillation takes place  
depending upon the conditions for the attachment of external components. In particular, take the utmost  
care when an inductor with a large inductance is used.  
The performance of power source circuits using these ICs largely depends upon the peripheral circuits. Take the utmost care in the  
selection of the peripheral circuits. In particular, design the peripheral circuits in such a manner that the values such as voltage, current  
and power of each component, PCB patterns and the IC do not exceed their respective rated values.  
29  
 
RICOH COMPANY, LTD.  
ELECTRONIC DEVICES DIVISION  
HEADQUARTERS  
13-1, Himemuro-cho, Ikeda City, Osaka 563-8501, JAPAN  
Phone 81-727-53-1111 Fax 81-727-53-6011  
YOKOHAMA OFFICE (International Sales)  
3-2-3, Shin-Yokohama, Kohoku-ku, Yokohama City, Kanagawa 222-8530,  
JAPAN  
Phone 81-45-477-1697 Fax 81-45-477-1694·1695  
RICOH CORPORATION  
ELECTRONIC DEVICES DIVISION  
SAN JOSE OFFICE  
3001 Orchard Parkway, San Jose, CA 95134-2088, U.S.A.  
Phone 1-408-432-8800 Fax 1-408-432-8375  
 

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