2CH PWM DC/DC CONTROLLER
R1282D002A
1
R1282E/2004/08/19
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.
R1282D002A
2
BLOCK DIAGRAM
PART NUMBER GUIDE
The selection can be made with designating the part number as shown below;
R1282D002A-TR
Part Number
a
V
IN
EXT1
OSC
Vref1
Latch
DTC2
V
FB2
Vrefout
EXT2
UVLO
GND
AMPOUT1
V
FB1
Vrefout
DTC1
Delay Circuit
CH1
CH2
Vref2
R1282D002A
3
Code
Contents
a
Designation of Taping Type :
(Refer to Taping Specifications.)
PIN CONFIGURATION
SON-10
PIN DESCRIPTION
Pin No.
Symbol
Description
1
EXT1
External Transistor of Channel 1 Drive Pin (CMOS Output)
2
GND
Ground Pin
3
AMPOUT1
Amplifier Output Pin of Channel 1
4
DTC1
Maximum Duty Cycle of Channel 1 Setting Pin
5
V
FB1
Feedback pin of Channel 1
6
V
FB2
Feedback pin of Channel 2
7
DTC2
Maximum Duty Cycle of Channel 2 Setting Pin
8
Vrefout
Reference Output Pin
9
V
IN
Voltage Supply Pin of the IC
10
EXT2
External Transistor of Channel 2 Drive Pin (CMOS Output)
10
1
(mark side)
R1282D002A
4
ABSOLUTE MAXIMUM RATINGS
Symbol
Item
Rating
Unit
V
IN
V
IN
Pin Voltage
6.5
V
V
EXT1,2
V
EXT1,2
Pin Output Voltage
-0.3~V
IN
+0.3
V
V
AMPOUT1
AMPOUT1 Pin Voltage
-0.3~V
IN
+0.3
V
V
DTC1,2
DTC1,2 Pin Voltage
-0.3~V
IN
+0.3
V
V
refout
V
REFOUT
Pin Voltage
-0.3~V
IN
+0.3
V
V
FB1,2
V
FB1
,V
FB2
Pin Voltage
-0.3~V
IN
+0.3
V
I
EXT1,2
EXT1,2 Pin Output Current
50
mA
P
D
Power Dissipation
250
mW
Topt
Operating Temperature Range
-40 to +85
C
Tstg
Storage Temperature Range
-55 to +125
C
ELECTRICAL CHARACTERISTICS
Topt=25C
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
V
IN
Operating Input Voltage
2.5
5.5
V
V
REFOUT
V
REFOUT
Voltage Tolerance
V
IN
=3.3V, I
OUT
=1mA
1.478
1.500
1.522
V
I
ROUT
V
REFOUT
Output Current
V
IN
=3.3V
20
mA
V
REFOUT
/
V
IN
V
REFOUT
Line Regulation
2.5V
V
IN
5.5V
2
6
mV
V
REFOUT
/
I
OUT
V
REFOUT
Load Regulation
1mA
I
ROUT
10mA V
IN
=3.3V
6
12
mV
I
LIM
V
REFOUT
Short Current Limit
V
IN
=3.3V, V
REFOUT
=0V
25
mA
V
REFOUT
/
T V
REFOUT
Voltage Temperature Coefficient -40C Topt 85C
150
ppm/C
V
FB1
V
FB1
Voltage
V
IN
=3.3V
0.985
1.000
1.015
V
V
FB1
/
T V
FB1
Voltage Temperature Coefficient -40C
Topt 85C
150
ppm/C
V
FB2
/
T V
FB2
Voltage Temperature Coefficient -40C
Topt 85C
150
ppm/C
I
VFB1,2
V
FB1,2
Input Current
V
IN
=5.5V,V
FB1
or V
FB2
=0V or 5.5V
-0.1
0.1
A
f
OSC
Oscillator Frequency
EXT1,2 Pins at no load, V
IN
=3.3V
595
700
805
kHz
I
DD1
Supply Current
V
IN
=5.5V, EXT1,2 pins at no load
1.4
3.0
mA
R
EXTH1
EXT1 "H" ON Resistance
V
IN
=3.3V, I
EXT
=-20mA
4.0
8.0
R
EXTL1
EXT1 "L" ON Resistance
V
IN
=3.3V, I
EXT
=20mA
2.7
5.0
R
EXTH2
EXT2 "H" ON Resistance
V
IN
=3.3V, I
EXT
=-20mA
4.0
8.0
R
EXTL2
EXT2 "L" ON Resistance
V
IN
=3.3V, I
EXT
=20mA
3.7
8.0
T
DLY
Delay Time for Protection
V
IN
=3.3V, V
FB1
=1.1V
0V
60
100
140
ms
V
UVLOD
UVLO Detector Threshold
2.10
2.20
2.35
V
V
UVLO
UVLO Released Voltage
V
UVLOD
+0.20
2.48
V
R1282D002A
5
V
DTC10
CH1 Duty=0%
V
IN
=3.3V
0.1
0.2
0.3
V
V
DTC1100
CH1 Duty=100%
V
IN
=3.3V
1.1
1.2
1.3
V
V
DTC20
CH2 Duty=0%
V
IN
=3.3V
0.1
0.2
0.3
V
V
DTC2100
CH2 Duty=100%
V
IN
=3.3V
1.1
1.2
1.3
V
A
V1
CH1 Open Loop Gain
V
IN
=3.3V
110
dB
F
T1
CH1 Single Gain Frequency Band
V
IN
=3.3V, A
V1
=0dB
1.9
MHz
V
ICR1
CH1 Input Voltage Range
V
IN
=3.3V
0.7 to V
IN
V
I
AMPL
CH1 Sink Current
V
IN
=3.3V, V
AMPOUT1
=1.0V,
V
FB1
=V
FB1
+ 0.1V
70
115
A
I
AMPH
CH1 Source Current
V
IN
=3.3V, V
AMPOUT1
=1.0V,
V
FB1
=V
FB1
- 0.1V
-1.4
-0.7
mA
A
V2
CH2 Open Loop Gain
V
IN
=3.3V
60 dB
F
T2
CH2 Single Gain Frequency Band
V
IN
=3.3V,
A
V2=0dB
600
kHz
V
ICR2
CH2 Input Voltage Range
V
IN
=3.3V
-0.2 to
V
IN
-1.3
V
V
FB2
CH2 Reference Voltage
V
IN
=3.3V
0.985
1.000
1.015
V
R1282D002A
6
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 L
X
Transistor on input voltage.
Inductor
Diode
C
L
Lx Tr
V
IN
V
OUT
I
OUT
ILxmax
ILxmin
Ton Toff
T=1/fosc
Tf
IL
Discontinuous Mode
t
ILxmax
ILxmin
Ton Toff
T=1/fosc
t
IL
Iconst
Continuous Mode
<Current through L>
GND
Step 1. L
X
Tr. is on, then the current IL=i1 flows, and the energy is charged in L. In proportion to the
on time of L
X
Tr. (Ton), IL=i1 increases from IL=IL
X
min=0 and reaches IL
X
max.
Step 2. When the L
X
Tr. is off, L turns on Schottky Diode (SD), and IL=i2 flows to maintain
IL=IL
X
max.
Step 3. IL=i2 gradually decreases, and after Tf passes, IL=IL
X
min=0 is true, then SD turns off. Note
that in the case of the continuous mode, before IL=IL
X
min=0 is true, Toff passes, and the
next cycle starts, then L
X
Tr. turns on again.
In this case, IL
X
min>0, therefore IL=IL
X
min>0 is another starting point and IL
X
max
increases.
With the PWM controller, switching times during the time unit are fixed. By controlling T
on
, output
voltage is maintained.
R1282D002A
7
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 V
IN
, the
current is V
IN
t/L.
Therefore, the electric power, P
ON
, which is supplied with input side, can be described as in next
formula.
dt
L
/
t
V
P
Ton
0
2
IN
ON
=
..................................................................................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 (V
OUT
-V
IN
)t/L, therefore electric power, P
OFF
is described as in next
formula.
dt
L
/
t
)
V
V
(
V
P
IN
OUT
Tf
0
IN
OFF
-
=
.................................................................Formula 2
In this formula, Tf means the time of which the energy saved in the inductance is being emitted. Thus
average electric power, P
AV
is described as in the next formula.
}
dt
L
/
t
)
V
V
(
V
dt
L
/
t
V
{
)
Toff
Ton
/(
1
P
IN
OUT
Tf
0
IN
Ton
0
2
IN
AV
-
+
+
=
..........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.
V
IN
Ton/L=(V
OUT
-V
IN
)Toff/L ....................................................................................Formula 4
Further, the electric power, P
AV
is equal to output electric power, V
OUT
I
OUT
, thus,
I
OUT
= f
OSC
V
IN
2
Ton
2
/{2L (V
OUT
-V
IN
)}=V
IN
2
Ton/(2LV
OUT
)..............................Formula 5
When I
OUT
becomes more than V
IN
TonToff/(2L(Ton+Toff)), the current flows through the inductor,
then the mode becomes continuous. The continuous current through the inductor is described as
Iconst, then,
I
OUT
= f
OSC
V
IN
2
Ton
2
/(2L(V
OUT
-V
IN
))+V
IN
Iconst/V
OUT
........................................Formula 6
R1282D002A
8
In this moment, the peak current, IL
X
max flowing through the inductor and the driver Tr. is described
as follows:
IL
X
max = Iconst +V
IN
Ton/L .......................................................................... Formula 7
With the formula 4,6, and IL
X
max is,
IL
X
max = V
OUT
/V
IN
I
OUT
+V
IN
Ton/(2L) ...................................................................Formula 8
Therefore, peak current is more than I
OUT
. Considering the value of IL
X
max, the condition of input and
output, and external components should be selected.
In the formula 7, peak current IL
X
max 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 L
X
switch and external
components is not included. The actual maximum output current is between 50% and 80% of the
calculation. Especially, when the IL
X
is large, or V
IN
is low, the loss of V
IN
is generated with the on
resistance of the switch. As for V
OUT
, Vf (as much as 0.3V) of the diode should be considered.
Operation of Step-down 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>
Basic Circuits>
Basic Circuits>
Basic Circuits>
SD
L
CL
V
OU
I
OU
V
I
Lx
i1
i2
T=1/fos
c
toff
to n
ILma
x
ILmi
n
topen
R1282D002A
9
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.
G 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 = V
OUT
topen / L = (V
IN
-V
OUT
)
ton/L
Equation A
wherein, T=1/fosc=ton+toff
duty (%)=ton/T
100=ton
fosc
100
topen
toff
In Equation A, V
OUT
topen/L and (V
IN
-V
OUT
)
ton/L are respectively shown the change of the current at ON,
and the change of the current at OFF.
When the output current (I
OUT
) 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 I
OUT
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
V
OUT
/V
IN
Equation B
When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.
R1282D002A
10
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
V
IN
- V
OUT
the current is (V
IN
- V
OUT
) t/L.
Therefore, the electric power, P, which is supplied from the input side, can be described as in next
formula.
Ton
P=V
IN
(V
IN
-V
OUT
)t/ L dt
Formula
9
0
Thus average electric power in one cycle, P
AV
is described as in the next formula.
Ton
P
AV
= 1(Ton+Toff)V
IN
(V
IN
-V
OUT
)t/ L dt = V
IN
(V
IN
-V
OUT
)Ton
2
/ (2L (Ton+Toff))
Formula
10
0
This electric power P
AV
equals to output electric power V
OUT
I
OUT
, thus,
I
OUT
= V
IN
/ V
OUT
(V
IN
V
OUT )
Ton
2
/(2L(Ton+Toff))............................................Formula 11
When I
OUT
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,
(V
IN
V
OUT )
Ton/L=V
OUT
Toff/L ...............................................................................Formula 12
In this moment, the current flowing continuously through L, is assumed as Iconst, I
OUT
is described as
in the next formula:
I
OUT
=I
CONST
+V
OUT
T
OFF
/(2L) ...................................................................................Formula 13
In this moment, the peak current, IL
X
max flowing through the inductor and the driver Tr. is described
as follows:
IL
X
max=I
OUT
+V
OUT
Toff/(2L) ...............................................................................Formula 14
With the formula 12,13, Toff is,
Toff=(1-V
OUT
/V
IN
)/f
OSC
.............................................................................................Formula 15
R1282D002A
11
Therefore, peak current is more than I
OUT
. Considering the value of IL
X
max, the condition of input and
output, and external components should be selected.
In the formula 14, peak current IL
X
max 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 L
X
switch and external
components is not included.
TEST CIRCUITS
Test Circuit 1
Test Circuit 2
Test Circuit 3
Test Circuit 4
C1
C2
EXT1
GND
DTC1
VFB1
VFB2
DTC2
VREFOUT
VIN
OSCILLOSCOPE
C1
C2
OSCILLOSCO
PE
EXT2
GND
VIN
VREFOUT
DTC1 DTC2
V
FB1
VFB2
C1
C2
OSCILLOSCOPE
EXT1
GND
VIN
VREFOUT
DTC1
DTC2
VFB1
VFB2
C1
C2
OSCILLOSCOPE
DTC2
DTC1
VIN
VFB1
VREFOUT
EXT2
GND
VFB2
R1282D002A
12
Test Circuit 5
Test Circuit 6
Test Circuit 7
Test Circuit 8
Test Circuit 9
Test Circuit 10
Typical Characteristics shown in the following pages are obtained with test circuits shown above.
Test Circuit 1,2: Typical Characteristic 4)
Test Circuit 3:
Typical Characteristic 5)
Test Circuit 4:
Typical Characteristic 5)
C1
C2
V
GND
VIN
VREFOUT
DTC1
DTC2
VFB1
VFB2
C1
C2
V
GND
VIN
VREFOUT
DTC1
DTC2
VFB1
VFB2
A
C1
C2
OSC
ILLOSCOPE
EXT1
GND
VIN
VREFOUT
DTC1
DTC2
VFB1
VFB2
OS
C
ILLOSC
O
PE
C1
C2
EXT1
GND
VIN
VREFOUT
DTC1 DTC2
VFB1
VFB2
OSCILLOSCOPE
EXT2
GND
VIN
VREFOUT
DTC1
DTC2
VFB1
VFB2
C1
C2
DTC2
DTC1
VFB1
VREFOUT
GND
VFB2
A
C1
C2
VIN
AMPOUT1
R1282D002A
13
Test Circuit 5:
Typical Characteristic 6)
Test Circuit 6:
Typical Characteristics 7) 8)
Test Circuit 7:
Typical Characteristic 9)
Test Circuit 8:
Typical Characteristic 10)
Test Circuit 9:
Typical Characteristics 10)
Test Circuit 10:
Typical Characteristics 11) 12)
Note) Capacitors' values of test circuits
Capacitors: Ceramic Type:
C1=4.7F,
C2=1.0F
Efficiency (%) can be calculated with the next formula:
=(V
OUT1
I
OUT1
+V
OUT2
I
OUT2
)/(V
IN
I
IN
)100
TYPICAL CHARACTERISTICS
1) Output Voltage vs. Output Current (Topt=25
C)
R1282D002A
R1282D002A
9.9
9.95
10
10.05
10.1
0
50
100
150
200
Output Current Iout1(mA)
O
u
tput Voltage Vout1(V)
Vin=2.8V
Vin=3.3V
Vin=5.5V
L1=6.8uH, C1=10uF, Vout2=2.5V, Iout2=0mA
2.4
2.45
2.5
2.55
2.6
0
100
200
300
400
500
600
Output Current Iout1(mA)
Out
put
V
o
lt
age V
out
1(V
)
Vin=2.8V
Vin=3.3V
Vin=5.5V
L2=6.8HC2=10FVout1=10VIout1=0mA
R1282D002A
14
2) Efficiency vs. Output Current (V
IN
=3.3V, Topt=25C)
R1282D002A
R1282D002A
0
10
20
30
40
50
60
70
80
90
0
50
100
150
200
Output Current Iout(mA)
E
f
f
i
c
i
enc
y (%
)
Vout1=5V
Vout1=10V
Vout1=15V
L1=6.8H, C1=10F, Vout2=2.5V,
I t2 0 A
0
10
20
30
40
50
60
70
80
90
0
100
200
300
400
500
600
Output Current Iout(mA)
E
fficiency
(
%
)
Vout2=1.8V
Vout2=2.5V
L2=6.8H, C2=10F, Vout1=10V, Iout1=0mA
3) Output Voltage vs. Temperature (V
IN
=3.3V)
R1282D002A
R1282D002A
9
9.5
10
10.5
11
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(
C)
Out
put
V
o
l
t
age V
out
1(V
)
Iout=10mA
Iout=100m
A
L1=6.8H, C1=10F
2
2.25
2.5
2.75
3
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(C)
Out
put
V
o
l
t
age V
out
2(V
)
Iout=10mA
Iout=100mA
Iout=200mA
L2=6.8H, C2=10F
4) Frequency vs. Temperature
R1282D002A
550
600
650
700
750
800
-60
-40
-20
0
20
40
60
80
100
Temperature Topt[
C]
Os
c
illat
o
r Frequenc
y
f
o
s
c
[
k
H
z
]
VIN=2.5V
VIN=3.3V
VIN=5.5V
R1282D002A
15
5) Feedback Voltage vs. Temperature (V
IN
=3.3V)
R1282D002A
R1282D002A
0.97
0.98
0.99
1
1.01
1.02
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(C)
Feedbac
k
V
o
l
t
age V
F
B
1
(V
)
0.97
0.98
0.99
1
1.01
1.02
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(C)
Feedbac
k
V
o
l
t
age V
F
B
2
[
V
]
6)Vrefout Voltage vs. Temperature(V
IN
=3.3V) 7)Vrefout Output Voltage vs. Output Current
R1282D002A
R1282D002A
1.45
1.47
1.49
1.51
1.53
1.55
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(
C)
V
r
efout V
o
ltage (
V
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
10
20
30
40
50
60
70
80
IROUT(mA)
V
r
ef
out
V
o
l
t
age (V
)
Vin=2.5V
Vin=3.3V
Vin=5.5V
8) Vrefout Output Voltage vs. Output Current
9) Protection Delay Time vs. Temperature (V
IN
=3.3V)
R1282D002A
R1282D002A
1.498
1.5
1.502
1.504
1.506
1.508
1.51
0
5
10
15
20
IROUT(mA)
V
r
ef
out
V
o
l
t
age(V
)
Vin=2.5V
Vin=3.3V
Vin=5.5V
60
80
100
120
140
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(
C)
P
r
otec
tion D
e
lay
Tim
e
T
DL
Y
(m
s
)
R1282D002A
16
10) Maximum Duty Cycle vs. DTC Voltage (V
IN
=3.3V)
R1282D002A
R1282D002A
0
20
40
60
80
100
0
0.2
0.4
0.6
0.8
1
1.2
1.4
DTC1 Voltage(V)
C
H
1
Ma
ximu
m D
u
ty C
ycle
Dut
y
1(%
)
0
20
40
60
80
100
0
0.2
0.4
0.6
0.8
1
1.2
1.4
DTC2 Voltage(V)
CH2
Ma
x
i
mu
m Du
t
y
Du
t
y
2
(
%)
11)Output Sink Current vs. Temperature (V
IN
=3.3V)
12) Output Source Current vs. Temperature
R1282D002A
R1282D002A
90
100
110
120
130
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(C)
Out
put
S
i
nk
Current
I
AM
PL
(
A
)
-3
-2.5
-2
-1.5
-1
-0.5
0
-60
-40
-20
0
20
40
60
80
100
Temperature Topt(C)
Out
put
S
ourc
e
Current
I
AM
PH
(
A
)
13) Load Transient Response (Step-up Side) V
IN
=3.3V, L1=6.8
H
R1282D002A
R1282D002A
7.5
8
8.5
9
9.5
10
10.5
0.0000
0.0005
0.0010
0.0015
0.0020
Time (s)
O
u
t
p
ut
V
o
lt
age
Vout1(V)
0
0.05
0.1
0.15
0.2
0.25
0.3
O
u
tput C
u
rrent I
OUT
(A)
1.5
1.75
2
2.25
2.5
2.75
3
0.00
0.01
0.02
0.03
0.04
Time (s)
O
u
tput Voltage Vout2(V)
0
0.05
0.1
0.15
0.2
0.25
0.3
O
u
tput C
u
rrent I
OUT
(A)
R1282D002A
17
14) Load Transient Response (Step-down Side) V
IN
=3.3V, L2=6.8
H
R1282D002A
R1280D002A
1.5
1.75
2
2.25
2.5
2.75
3
0.0000
0.0005
0.0010
0.0015
0.0020
Time (s)
Out
put
V
o
l
t
age V
out
2(V
)
0
0.05
0.1
0.15
0.2
0.25
0.3
Out
put
Current
I
OUT
(A
)
1.5
1.75
2
2.25
2.5
2.75
3
0.00
0.01
0.02
0.03
0.04
Time (s)
Out
put
V
o
l
t
age V
out
2(V
)
0
0.05
0.1
0.15
0.2
0.25
0.3
Out
put
Current
I
OUT
(A
)
TYPICAL APPLICATION
Components examples
Inductor L1,2
6.8H LDR655312T (TDK)
Diode
FS1J3 (Origin Electronics)
PMOS
Si3443DV (Siliconix)
NMOS IRF7601 (International Rectifier)
Resistance As setting resistors total value for the output voltage, R1R2, R3+R4 recommendation value is 100k
or less.
R1=47k
R2=5.1k
R3=30k R4=20k
R5=43k
R6=10k
R7=R9=22k
R8=R10=43k R11=220k
Capacitors Ceramic Type
C1=C2=10F
C3=4.7F C4=0.22F C5=0.47F C6=120pF
C7=50pF
C8=1F C9=1000pF
Note) Consider the ratings of external components including voltage tolerance. With the transistor in the circuit above, V
OUT
=15V
is the voltage setting limit.
L2
NMOS
R5
L1
EXT1 EXT2
GND
AMPOUT1
Vrefout
DTC1 DTC2
VFB1
VFB2
R1
R2
C1
PMOS
C8
R3
R4
C2
C9
R11
VOUT1
VOUT2
R9
Diode
R6
C7
Diode
C6
C4
R7
R8
C3
VIN
C5 R 10
R1282D002A
18
EXTERNAL COMPONENTS
1. How to set the output voltages
As for step-up side, feedback (V
FB1
) pin voltage is controlled to maintain 1V, therefore,
V
OUT1
: R1+R2=V
FB1
: R2
Thus, V
OUT1
=V
FB1
(R1+R2)/R2
Output Voltage is adjustable with R1 and R2.
As for Step-down side, Feedback (V
FB2
) pin voltage follows the next formula,
V
OUT2
: R3+R4=V
FB2
: R4
Thus, V
OUT2
=V
FB2
(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, T
SS1
and T
SS2
are adjustable. Soft-start time can be set with the time constant of
RC.
Soft-start time can be described as in next formula.
T
SS1
RO1C4
If R10=0, then,
T
SS2
R9C5ln((Vrefout-V
DTC2
)/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.
R1282D002A
19
TECHNICAL NOTES on EXTERNAL COMPONENTS
External components should be set as close to this IC as possible. Especially, wiring of the
capacitor connected to V
IN
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 4.7F.
If the spike noise of V
OUT1
is too large, the noise is feedback from V
FB1
pin and operation might be
unstable. In that case, use the resistor ranging from 10k
to 50k
as R5 and try to reduce the
noise level. In the case of V
OUT2
, use the resistor as much as 10k
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, IL
X
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 10F. In case that the
operation with the system of DC/DC converter would be unstable, add a series resister less than
0.5
to each output capacitor or use tantalum capacitors with appropriate ESR. If you choose too
large ESR, ripple noise may be forced to V
FB1
and V
FB2
, and unstable operation may result. Use a
capacitor with fully large voltage tolerance of the capacitor.
In this IC, for the test efficiency, latch release function is included. By forcing (V
IN
-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.
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