2CH PWM DC/DC CONTROLLER
R1282D002A SERIES
NO. EA-086-0502
OUTLINE
The R1282D002A is a CMOS-based 2-channel PWM Step-up (as Channel 1)/Step-down (as Channel 2)
DC/DC converter controller.
The R1282D002A consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a
reference current unit, a protection circuit, and an under voltage lockout (UVLO) circuit. A high efficiency
Step-up/Step-down DC/DC converter can be composed of this IC with inductors, diodes, power MOSFETs,
resisters, and capacitors. Each output voltage and maximum duty cycle can be adjustable with external resistors,
while soft-start time can be adjustable with external capacitors and resistors.
As for a protection circuit, if Maximum duty cycle of either Step-up DC/DC converter side or Step-down DC/DC
converter side is continued for a certain time, the R1280D002A latches both external drivers with their off state
by its Latch-type protection circuit. Delay time for protection is internally fixed typically at 100ms. To release the
protection circuit, restart with power-on (Voltage supplier is equal or less than UVLO detector threshold level).
FEATURES
•
•
•
•
•
•
Input Voltage Range .........................................2.5V to 5.5V
Built-in Latch-type Protection Function by monitoring duty cycle (Fixed Delay Time Typ. 100ms)
Oscillator Frequency .........................................700kHz
High Accuracy Voltage Reference ....................±1.5%
U.V.L.O. Threshold............................................Typ. 2.2V (Hysteresis: Typ. 0.2V)
Small Package ..................................................thin SON-10 (package thickness Max. 0.9mm)
APPLICATIONS
• Constant Voltage Power Source for Portable Equipment.
• Constant Voltage Power Source for LCD and CCD.
1
R1282D002A
BLOCK DIAGRAM
DTC1
VFB1
EXT1
OSC
AMPOUT1
CH1
VIN
Vref1
Vrefout
GND
UVLO
Vrefout
EXT2
VFB2
Vref2
Latch
Delay Circuit
CH2
DTC2
SELECTION GUIDE
The selection can be made with designating the part number as shown below;
R1282D002A-TR ←Part Number
↑
a
Code
a
2
Contents
Designation of Taping Type :
(Refer to Taping Specifications.)
R1282D002A
PIN CONFIGURATION
SON-10
10 9 8 7 6
(mark side)
1 2 3 4 5
PIN DESCRIPTION
Pin No
Symbol
Description
1
EXT1
External Transistor of Channel 1 Drive Pin (CMOS Output)
2
GND
Ground Pin
3
AMPOUT1
4
DTC1
5
VFB1
Feedback pin of Channel 1
6
VFB2
Feedback pin of Channel 2
7
DTC2
Maximum Duty Cycle of Channel 2 Setting Pin
8
Vrefout
Reference Output Pin
9
VIN
10
EXT2
Amplifier Output Pin of Channel 1
Maximum Duty Cycle of Channel 1 Setting Pin
Voltage Supply Pin of the IC
External Transistor of Channel 2 Drive Pin (CMOS Output)
ABSOLUTE MAXIMUM RATINGS
Symbol
Rating
Unit
6.5
V
VEXT1,2 Pin Output Voltage
−0.3~VIN+0.3
V
AMPOUT1 Pin Voltage
−0.3~VIN+0.3
V
VDTC1,2
DTC1,2 Pin Voltage
−0.3~VIN+0.3
V
Vrefout
VREFOUT Pin Voltage
−0.3~VIN+0.3
V
VFB1,2
VFB1,VFB2 Pin Voltage
−0.3~VIN+0.3
V
IEXT1,2
EXT1,2 Pin Output Current
±50
mA
Power Dissipation
250
mW
VIN
VEXT1,2
VAMPOUT1
PD
Item
VIN Pin Voltage
Topt
Operating Temperature Range
−40 to +85
°C
Tstg
Storage Temperature Range
−55 to +125
°C
3
R1282D002A
ELECTRICAL CHARACTERISTICS
Topt=25°C
Symbol
VIN
VREFOUT
IROUT
Item
Operating Input Voltage
VREFOUT Voltage Tolerance
VIN=3.3V, IOUT=1mA
VREFOUT Output Current
VIN=3.3V
∆VREFOUT/∆VIN VREFOUT Line Regulation
∆VREFOUT/∆IOUT VREFOUT Load Regulation
ILIM
VREFOUT Short Current Limit
VREFOUT Voltage
∆VREFOUT/∆T
Temperature Coefficient
VFB1
VFB1 Voltage
VFB1 Voltage
∆VFB1/∆T
Temperature Coefficient
VFB2 Voltage
∆VFB2/∆T
Temperature Coefficient
IVFB1,2
VFB1,2 Input Current
fOSC
IDD1
REXTH1
REXTL1
REXTH2
REXTL2
TDLY
VUVLOD
Supply Current
EXT1 "H" ON Resistance
EXT1 "L" ON Resistance
EXT2 "H" ON Resistance
EXT2 "L" ON Resistance
Delay Time for Protection
UVLO Detector Threshold
VUVLO
UVLO Released Voltage
−40°C
<
=
1.500
Max.
5.5
1.522
Topt
<
=
mA
2
6
25
85°C
6
12
±150
0.985
Unit
V
V
1.000
mV
mV
mA
ppm/°C
1.015
V
−40°C
<
=
Topt
<
=
85°C
±150
ppm/°C
−40°C
<
=
Topt
<
=
85°C
±150
ppm/°C
VIN=5.5V,VFB1 or VFB2=0V or 5.5V
EXT1,2 Pins at no load,
VIN=3.3V
VIN=5.5V, EXT1,2 pins at no load
VIN=3.3V, IEXT=−20mA
VIN=3.3V, IEXT=20mA
VIN=3.3V, IEXT=−20mA
VIN=3.3V, IEXT=20mA
VIN=3.3V, VFB1=1.1V→0V
VICR1
CH1 Input Voltage Range
VIN=3.3V
IAMPL
CH1 Sink Current
IAMPH
CH1 Source Current
AV2
CH2 Open Loop Gain
CH2 Single Gain
Frequency Band
FT2
Typ.
20
VIN=3.3V
VIN=3.3V
VIN=3.3V
VIN=3.3V
VIN=3.3V
VIN=3.3V
FT1
Min.
2.5
1.478
2.5V <
= VIN <
= 5.5V
1mA <
= IROUT <
= 10mA VIN=3.3V
VIN=3.3V, VREFOUT=0V
CH1 Duty=0%
CH1 Duty=100%
CH2 Duty=0%
CH2 Duty=100%
CH1 Open Loop Gain
CH1 Single Gain
Frequency Band
VDTC10
VDTC1100
VDTC20
VDTC2100
AV1
4
Oscillator Frequency
Conditions
595
60
2.10
0.1
1.1
0.1
1.1
VIN=3.3V, AV1=0dB
VIN=3.3V,
VAMPOUT1=1.0V,VFB1=VFB1+ 0.1V
VIN=3.3V,
VAMPOUT1=1.0V,VFB1=VFB1− 0.1V
VIN=3.3V
70
CH2 Input Voltage Range
VIN=3.3V
VFB2
CH2 Reference Voltage
VIN=3.3V
µA
700
805
kHz
1.4
4.0
2.7
4.0
3.7
100
2.20
VUVLOD
+0.20
0.2
1.2
0.2
1.2
110
3.0
8.0
5.0
8.0
8.0
140
2.35
mA
Ω
Ω
Ω
Ω
ms
V
2.48
V
0.3
1.3
0.3
1.3
V
V
V
V
dB
1.9
MHz
0.7 to
VIN
V
115
µA
−1.4
VIN=3.3V, AV2=0dB
VICR2
0.1
−0.1
0.985
−0.7
mA
60
dB
600
kHz
−0.2 to
VIN−1.3
1.000
V
1.015
V
R1282D002A
Operation of Step-up DC/DC Converter and Output Current
Step-up DC/DC Converter makes higher output voltage than input voltage by releasing the energy
accumulated during on time of LX Transistor on input voltage.
<Basic Circuit>
i2
Inductor
IOUT
Diode
VIN
VOUT
i1
Lx Tr
CL
GND
<Current through L>
Discontinuous Mode
Continuous Mode
IL
ILxmax
IL
ILxmax
ILxmin
ILxmin
Tf
Iconst
t
Ton
T=1/fosc
Toff
t
Ton
T=1/fosc
Toff
Step 1. LX Tr. is on, then the current IL=i1 flows, and the energy is charged in L. In proportion to the on time of LX
Tr. (Ton), IL=i1 increases from IL=ILXmin=0 and reaches ILXmax.
Step 2. When the LX Tr. is off, L turns on Schottky Diode (SD), and IL=i2 flows to maintain IL=ILXmax.
Step 3. IL=i2 gradually decreases, and after Tf passes, IL=ILXmin=0 is true, then SD turns off. Note that in the
case of the continuous mode, before IL=ILXmin=0 is true, Toff passes, and the next cycle starts, then LX
Tr. turns on again.
In this case, ILXmin>0, therefore IL=ILXmin>0 is another starting point and ILX max increases.
With the PWM controller, switching times during the time unit are fixed. By controlling Ton, output voltage is
maintained.
5
R1282D002A
Output Current and Selection of External Components
Output Current of Step-up Circuit and External Components
There are two modes, or discontinuous mode and continuous mode for the PWM step-up switching regulator
depending on the continuous characteristic of inductor current.
During on time of the transistor, when the voltage added on to the inductor is described as VIN, the current is
VIN × t/L.
Therefore, the electric power, PON, which is supplied with input side, can be described as in next formula.
PON =
∫
Ton
0
VIN 2 × t/L dt ...................................................................................................Formula 1
With the step-up circuit, electric power is supplied from power source also during off time. In this case, input
current is described as (VOUT−VIN)×t/L, therefore electric power, POFF is described as in next formula.
POFF =
∫
Tf
0
VIN × (VOUT − VIN)t/L dt ...................................................................................Formula 2
In this formula, Tf means the time of which the energy saved in the inductance is being emitted. Thus average
electric power, PAV is described as in the next formula.
PAV = 1/(Ton + Toff) × {
∫
Ton
0
VIN2 × t/L dt +
∫
Tf
0
VIN × (VOUT − VIN)t/L dt} ............................Formula 3
In PWM control, when Tf=Toff is true, the inductor current becomes continuos, then the operation of switching
regulator becomes continuous mode.
In the continuous mode, the deviation of the current is equal between on time and off time.
VIN×Ton/L=(VOUT−VIN)×Toff/L ..........................................................................................Formula 4
Further, the electric power, PAV is equal to output electric power, VOUT×IOUT, thus,
IOUT = fOSC × VIN2×Ton2/{2×L ×(VOUT−VIN)}=VIN2×Ton/(2×L×VOUT)......................................Formula 5
When IOUT becomes more than VIN×Ton×Toff/(2×L×(Ton+Toff)), the current flows through the inductor, then the
mode becomes continuous. The continuous current through the inductor is described as
Iconst, then,
IOUT = fOSC×VIN2 ×Ton2/(2×L×(VOUT−VIN))+VIN×Iconst/VOUT ...............................................Formula 6
6
R1282D002A
In this moment, the peak current, ILXmax flowing through the inductor and the driver Tr. is described as
follows:
ILXmax = Iconst +VIN×Ton/L........................................................................................... Formula 7
With the formula 4,6, and ILXmax is,
ILXmax = VOUT/VIN×IOUT+VIN×Ton/(2×L)........................................................................... Formula 8
Therefore, peak current is more than IOUT. Considering the value of ILXmax, the condition of input and output,
and external components should be selected.
In the formula 7, peak current ILXmax at discontinuous mode can be calculated. Put Iconst=0 in the formula.
The explanation above is based on the ideal calculation, and the loss caused by LX switch and external
components is not included. The actual maximum output current is between 50% and 80% of the calculation.
Especially, when the ILX is large, or VIN is low, the loss of VIN is generated with the on resistance of the switch. As
for VOUT, Vf (as much as 0.3V) of the diode should be considered.
7
R1282D002A
Operation of Inverting DC/DC converter and Output Current
The step-down DC/DC converter charges energy in the inductor when Lx transistor is ON, and discharges the
energy from the inductor when Lx transistor is OFF and controls with less energy loss, so that a lower output
voltage than the input voltage is obtained. The operation will be explained with reference to the following
diagrams:
<Basic Circuits>
IL
ILxmax
i1
Lx Tr
Inductor
VIN
IOUT
VOUT
i2
SD
ILxmin
topen
CL
Ton
Toff
t
T=1/fosc
Step 1. Lx Tr. turns on and current IL (=i1) flows, and energy is charged into CL. At this moment, IL increases
from ILmin. (=0) to reach ILmax. in proportion to the on-time period(ton) of LX Tr.
Step 2. When Lx Tr. turns off, Schottky diode (SD) turns on in order that L maintains IL at ILmax, and current IL
(=i2) flows.
Step 3. IL decreases gradually and reaches ILmin. after a time period of topen, and SD turns off, provided that in
the continuous mode, next cycle starts before IL becomes to 0 because toff time is not enough. In this
case, IL value is from this ILmin (>0).
In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton),
with the oscillator frequency (fosc) being maintained constant.
Discontinuous Conduction Mode and Continuous Conduction Mode
The maximum value (ILmax) and the minimum value (ILmin) current which flow through the inductor is the
same as those when Lx Tr. is ON and when it is OFF.
The difference between ILmax and ILmin, which is represented by ∆I;
∆I = ILmax − ILmin = VOUT×topen / L = (VIN−VOUT) ×ton/L･･･Equation A
wherein, T=1/fosc=ton+toff
duty (%)=ton/T×100=ton× fosc ×100
topen <
= toff
In Equation A, VOUT×topen/L and (VIN−VOUT) ×ton/L are respectively shown the change of the current at ON,
and the change of the current at OFF.
When the output current (IOUT) is relatively small, topen < toff as illustrated in the above diagram. In this case,
the energy is charged in the inductor during the time period of ton and is discharged in its entirely during the time
period of toff, therefore ILmin becomes to zero (ILmin=0). When Iout is gradually increased, eventually, topen
becomes 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 continuous mode.
In the continuous mode, when Equation A is solved for ton and assumed that the solution is tonc,
tonc=T×VOUT/VIN･･･ Equation B
When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.
8
R1282D002A
Output Current and Selection of External Components
There are also two modes, or discontinuous mode and continuous mode for the PWM step-down switching
regulator depending on the continuous characteristic of inductor current.
During on time of the transistor, when the voltage added on to the inductor is described as VIN− VOUT the
current is (VIN− VOUT ) ×t/L.
Therefore, the electric power, P, which is supplied from the input side, can be described as in next formula.
P=
∫
Ton
0
VIN ･(VIN−VOUT)･t/ L dt ........................................................................................ Formula 9
Thus average electric power in one cycle, PAV is described as in the next formula.
PAV = 1/(Ton+Toff)
∫
Ton
0
VIN ･(VIN−VOUT)･t/ L dt = VIN･(VIN−VOUT)･Ton2 / (2･L (Ton+Toff)).... Formula 10
This electric power PAV equals to output electric power VOUT × IOUT, thus,
IOUT = VIN / VOUT× (VIN − VOUT )´Ton2/(2×L× (Ton+Toff)) ................................................. Formula 11
When IOUT increases and the current flows through the inductor continuously, then the mode becomes
continuous. In the continuous mode, the deviation of the current equals between Ton and Toff, therefore,
(VIN− VOUT ) ×Ton/L=VOUT×Toff/L .................................................................................. Formula 12
In this moment, the current flowing continuously through L, is assumed as Iconst, IOUT is described as in the
next formula:
IOUT=ICONST+VOUT×Toff /(2×L)......................................................................................... Formula 13
In this moment, the peak current, ILXmax flowing through the inductor and the driver Tr. is described as
follows:
ILXmax= IOUT +VOUT×Toff/(2×L)..................................................................................... Formula 14
With the formula 12,13, ILxmax is,
Toff=(1−VOUT/VIN)/fosc.................................................................................................. Formula 15
Therefore, peak current is more than IOUT. Considering the value of ILXmax, the condition of input and output,
and external components should be selected.
In the formula 14, peak current ILXmax at discontinuous mode can be calculated. Put Iconst=0 in the formula.
The explanation above is based on the ideal calculation, and the loss caused by LX switch and external
components is not included.
9
R1282D002A
TEST CIRCUITS
OSCILLOSCOPE
EXT1
C1
GND
C1
VIN
Vrefout
EXT2
C2
DTC1
DTC2
DTC1
DTC2
VFB1
VFB2
VFB1
VFB2
GND
C2
Test Circuit 2
OSCILLOSCOPE
EXT1
OSCILLOSCOPE
VIN
Vrefout
Test Circuit 1
C1
GND
EXT2
C1
VIN
GND
Vrefout
OSCILLOSCOPE
VIN
Vrefout
C2
C2
DTC1
DTC2
DTC1
DTC2
VFB1
VFB2
VFB1
VFB2
Test Circuit 3
C1
GND
C1
VIN
Vrefout
DTC1
DTC2
VFB1
VFB2
GND
C2
Test Circuit 5
10
Test Circuit 4
VIN
Vrefout
V
DTC1
DTC2
VFB1
VFB2
C2
Test Circuit 6
A
V
R1282D002A
OSCILLOSCOPE
EXT1
C1
GND
C1
VIN
Vrefout
EXT1
OSCILLOSCOPE
GND
C2
VIN
Vrefout
DTC1
DTC2
DTC1
DTC2
VFB1
VFB2
VFB1
VFB2
Test Circuit 7
C2
Test Circuit 8
EXT2
C1
GND
OSCILLOSCOPE
VIN
C1
A
Vrefout
GND
VIN
AMPOUT1
Vrefout
C2
C2
DTC1
DTC2
DTC1
DTC2
VFB1
VFB2
VFB1
VFB2
Test Circuit 9
Test Circuit 10
Typical Characteristics shown in the following pages are obtained with test circuits shown above.
Test Circuit 1,2 :
Test Circuit 3 :
Test Circuit 4 :
Test Circuit 5 :
Test Circuit 6 :
Test Circuit 7 :
Test Circuit 8 :
Test Circuit 9 :
Test Circuit 10 :
Typical Characteristic 4)
Typical Characteristic 5)
Typical Characteristic 5)
Typical Characteristic 6)
Typical Characteristics 7) 8)
Typical Characteristic 9)
Typical Characteristic 10)
Typical Characteristics 10)
Typical Characteristics 11) 12)
Note) Capacitors' values of test circuits
Capacitors: Ceramic Type:
C1=4.7µF, C2=1.0µF
Efficiency η(%) can be calculated with the next formula:
η=(VOUT1×IOUT1+VOUT2×IOUT2)/(VIN×IIN)×100
11
R1282D002A
TYPICAL CHARACTERISTICS
1) Output Voltage vs. Output Current (Topt=25°C)
R1282D002A
L1=6.8µH,C1=10µF,VOUT2=2.5V,IOUT2=0mA
10.05
10.00
9.95
9.90
VIN=2.8V
VIN=3.3V
VIN=5.5V
0
50
100
150
Output Current IOUT1(mA)
L2=6.8µH,C2=10µF,VOUT1=10V,IOUT1=0mA
2.60
Output Voltage VOUT1(V)
10.10
Output Voltage VOUT1(V)
R1282D002A
2.55
2.50
2.45
2.40
200
VIN=2.8V
VIN=3.3V
VIN=5.5V
0
100 200 300 400 500
Output Current IOUT1(mA)
600
2) Efficiency vs. Output Current (VIN=3.3V, Topt=25°C)
R1282D002A
L1=6.8µH,C1=10µF,VOUT2=2.5V,IOUT2=0mA
80
80
70
70
60
50
40
30
VOUT1=5V
VOUT1=10V
VOUT1=15V
20
10
0
0
50
100
150
Output Current IOUT(mA)
L2=6.8µH,C2=10µF,VOUT1=10V,IOUT1=0mA
90
Efficiency (%)
Efficiency (%)
90
R1282D002A
60
50
40
30
20
VOUT2=1.8V
VOUT2=2.5V
10
0
200
0
100 200 300 400 500
Output Current lOUT(mA)
600
3) Output Voltage vs. Temperature (VIN=3.3V)
R1282D002A
R1282D002A
L1=6.8µH,C1=10µF
L2=6.8µH,C2=10µF
3.00
10.5
10.0
9.5
IOUT=10mA
IOUT=100mA
9.0
-60 -40 -20 0 20 40 60
Temperature Topt(°C)
12
80 100
Output Voltage VOUT2(V)
Output Voltage VOUT1(V)
11.0
2.75
2.50
2.25
IOUT=10mA
IOUT=100mA
IOUT=200mA
2.00
-60 -40 -20 0 20 40 60
Temperature Topt(°C)
80 100
R1282D002A
4) Frequency vs. Temperature
Oscillator Frequency fosc(kHz)
R1282D002A
800
750
700
650
VIN=2.5V
VIN=3.3V
VIN=5.5V
600
550
-60 -40 -20 0 20 40 60 80 100
Temperature Topt(°C)
5) Feedback Voltage vs. Temperature (VIN=3.3V)
R1282D002A
R1282D002A
1.02
Feedback Voltage VFB2(V)
Feedback Voltage VFB1(V)
1.02
1.01
1.00
0.99
0.98
0.97
1.01
1.00
0.99
0.98
0.97
-60 -40 -20 0 20 40 60 80 100
Temperature Topt(°C)
6) Vrefout Voltage vs. Temperature(VIN=3.3V)
-60 -40 -20 0 20 40 60 80
Temperature Topt(°C)
100
7) Vrefout Output Voltage vs. Output Current
R1282D002A
R1282D002A
1.8
1.55
Vrefout Voltage (V)
Vrefout Voltage (V)
1.6
1.53
1.51
1.49
1.47
VIN=3.3V
1.2
VIN=2.5V
1.0
0.8
VIN=5.5V
0.6
0.4
0.2
1.45
-60 -40 -20
1.4
0.0
0 20 40
Temp(°C)
60
80 100
0
10 20 30 40 50 60 70
Vrefout Output Current(mA)
80
13
R1282D002A
8) Vrefout Output Voltage vs. Output Current
9) Protection Delay Time vs. Temperature (VIN=3.3V)
R1282D002A
R1282D002A
Porotection Delay Time TDLY (ms)
Vrefout Voltage (V)
1.510
1.508
VIN=3.3V
1.506
VIN=5.5V
VIN=2.5V
1.504
1.502
1.500
1.498
0
5
10
15
Vrefout Output Current(mA)
20
140
120
100
80
60
-60 -40 -20 0 20 40 60
Temperature Topt(°C)
80 100
10) Maximum Duty Cycle vs. DTC Voltage (VIN=3.3V)
R1282D002A
CH2 Maximum Duty Cycle Duty2 (%)
CH1 Maximum Duty Cycle Duty1 (%)
R1282D002A
100
80
60
40
20
0
0.0
0.2
0.4 0.6 0.8 1.0
DTC1 Voltage(V)
1.2
1.4
11) Output Sink Current vs. Temperature (VIN=3.3V)
100
80
60
40
20
0
0.0
0.2
110
100
90
-60 -40
14
-20 0 20 40 60 80 100
Temperature Topt(°C)
1.4
R1282D002A
Output Source Current IAMPH (µA)
Output Sink Current IAMPL (µA)
120
1.2
12) Output Source Current vs. Temperature
R1282D002A
130
0.4 0.6 0.8 1.0
DTC2 Voltage(V)
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-60 -40
-20 0 20 40 60 80 100
Temperature Topt(°C)
R1282D002A
13) Load Transient Response (Step-up Side) VIN=3.3V, L1=6.8µH
0.25
9.5
0.20
9.0
0.15
8.5
0.10
8.0
0.05
7.5
0.0000
0.0005
0.0010 0.0015
Time (s)
0.00
0.0020
11.5
0.30
11.0
0.25
10.5
0.20
10.0
0.15
9.5
0.10
9.0
0.05
8.5
0.00
0.01
0.02
Time (s)
0.03
Output Current IOUT(A)
10.0
Output Voltage VOUT1(V)
R1282D002A
0.30
Output Current IOUT(A)
Output Voltage VOUT1(V)
R1282D002A
10.5
0.00
0.04
14) Load Transient Response (Step-down Side) VIN=3.3V, L2=6.8µH
0.30
2.75
0.25
2.50
0.20
2.25
0.15
2.00
0.10
1.75
0.05
1.50
0.0000
0.0005
0.0010 0.0015
Time (s)
0.00
0.0020
3.00
0.30
2.75
0.25
2.50
0.20
2.25
0.15
2.00
0.10
1.75
0.05
1.50
0.00
0.01
0.02
Time (s)
0.03
Output Current IOUT(A)
3.00
Output Voltage VOUT2(V)
R1280D002A
Output Current IOUT(A)
Output Voltage VOUT2(V)
R1282D002A
0.00
0.04
15
R1282D002A
TYPICAL APPLICATION AND TECHNICAL NOTES
VOUT1
Diode
L1
C1
C3
EXT1
EXT2
GND
VIN
PMOS
NMOS
R1
L2
C6
AMPOUT1
Vrefout
C9
R2
R5
R7
R11 C4
R9
DTC1
Components examples
Inductor L1,2
Diode
PMOS
NMOS
C7
R3
DTC2
R8
C5
VFB1
C8
VOUT2
R10
Diode
VFB2
C2
R6
R4
6.8µH LDR655312T (TDK)
FS1J3 (Origin Electronics)
Si3443DV (Siliconix)
IRF7601 (International Rectifier)
Resistance As setting resistors total value for the output voltage, R1+R2, R3+R4 recommendation value is
100kW or less.
R1=47kΩ
R2=5.1kΩ
R3=30kΩ
R4=20kΩ
R5=43kΩ
R6=10kWΩ
R7=R9=22kΩ R8=R10=43kΩ R11=220kΩ
Capacitors Ceramic Type
C1=C2=10µF C3=4.7µF
C7=50pF
C8=1µF
C4=0.22µF
C9=1000pF
C5=0.47µF
C6=120pF
Note) Consider the ratings of external components including voltage tolerance. With the transistor in the circuit
above, VOUT=15V is the voltage setting limit.
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R1282D002A
EXTERNAL COMPONENTS
1. How to set the output voltages
As for step-up side, feedback (VFB1) pin voltage is controlled to maintain 1V, therefore,
VOUT1: R1+R2=VFB1: R2
Thus, VOUT1=VFB1×(R1+R2)/R2
Output Voltage is adjustable with R1 and R2.
As for Step-down side, Feedback (VFB2) pin voltage follows the next formula,
VOUT2: R3+R4=VFB2 : R4
Thus, VOUT2=VFB2×(R3+R4)/R4
Output Voltage is adjustable with R3 and R4.
2. How to set Soft-Start Time and Maximum Duty Cycle
Soft-start time is adjustable with connecting resistors and a capacitor to DTC pin.
Soft starting time, TSS1 and TSS2 are adjustable. Soft-start time can be set with the time constant of RC.
Soft-start time can be described as in next formula.
TSS1≅RO1×C4
If R10=0Ω, then,
TSS2≅R9×C5×ln((Vrefout−VDTC2)/Vrefout)
Maximum Duty Cycle is set with the voltage to DTC1 and DTC2.
Maximum duty cycle is described as follows;
CH1 (Step-up side)
Maxduty1≅ (R8/(R7+R8) ×Vrefout−0.2)/(1.2−0.2) ×100 (%)
Step-up side maximum duty cycle should be set equal or less than 90%. If the maximum duty cycle is set at
high percentage, operation will be unstable.
17
R1282D002A
TECHNICAL NOTES on EXTERNAL COMPONENTS
• External components should be set as close to this IC as possible. Especially, wiring of the capacitor
connected to VIN pin should be as short as possible.
• Enforce the ground wire. Large current caused by switching operation flows through GND pin. If the
impedance of ground wire is high, internal voltage level of this IC might fluctuate and operation could be
unstable.
• Recommended capacitance value of C3 is equal or more than 4.7µF.
• If the spike noise of VOUT1 is too large, the noise is feedback from VFB1 pin and operation might be unstable.
In that case, use the resistor ranging from 10kΩ to 50kΩ as R5 and try to reduce the noise level. In the case
of VOUT2, use the resistor as much as 10kΩ as R6.
• Select an inductor with low D.C. current, large permissible current, and uneasy to cause magnetic
saturation. If the inductance value is too small, ILX might be beyond the absolute maximum rating at the
maximum load.
• Select a Schottky diode with fast switching speed and large enough permissible current.
• Recommended capacitance value of C1 and C2 is as much as Ceramic 10µF. In case that the operation
with the system of DC/DC converter would be unstable, add a series resister less than 0.5Ω to each output
capacitor or use tantalum capacitors with appropriate ESR. If you choose too large ESR, ripple noise may
be forced to VFB1 and VFB2, and unstable operation may result. Use a capacitor with fully large voltage
tolerance of the capacitor.
• this IC, for the test efficiency, latch release function is included. By forcing (VIN−0.3)V or more voltage to
DTC1 pin or DTC2 pin, Latch release function works.
• Performance of the power controller with using this IC depends on external components. Each component,
layout should not be beyond each absolute maximum rating such as voltage, current, and power
dissipation.
18