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2CH PWM DC/DC CONTROLLER
R1282D002A SERIES
OUTLINE
NO. EA-086-0502
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
OSC
EXT1
AMPOUT1
CH1 Vref1
VIN GND
Vrefout
Vrefout
UVLO
VFB2
Vref2
EXT2
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 Designation of Taping Type : (Refer to Taping Specifications.) Contents
2
R1282D002A
PIN CONFIGURATION
SON-10
10 9 8 7 6
(mark side)
12345
PIN DESCRIPTION
Pin No 1 2 3 4 5 6 7 8 9 10 Symbol EXT1 GND AMPOUT1 DTC1 VFB1 VFB2 DTC2 Vrefout VIN EXT2 Ground Pin Amplifier Output Pin of Channel 1 Maximum Duty Cycle of Channel 1 Setting Pin Feedback pin of Channel 1 Feedback pin of Channel 2 Maximum Duty Cycle of Channel 2 Setting Pin Reference Output Pin Voltage Supply Pin of the IC External Transistor of Channel 2 Drive Pin (CMOS Output) Description External Transistor of Channel 1 Drive Pin (CMOS Output)
ABSOLUTE MAXIMUM RATINGS
Symbol VIN VEXT1,2 VAMPOUT1 VDTC1,2 Vrefout VFB1,2 IEXT1,2 PD Topt Tstg VIN Pin Voltage VEXT1,2 Pin Output Voltage AMPOUT1 Pin Voltage DTC1,2 Pin Voltage VREFOUT Pin Voltage VFB1,VFB2 Pin Voltage EXT1,2 Pin Output Current Power Dissipation Operating Temperature Range Storage Temperature Range Item Rating 6.5 -0.3~VIN+0.3 -0.3~VIN+0.3 -0.3~VIN+0.3 -0.3~VIN+0.3 -0.3~VIN+0.3 50 250 -40 to +85 -55 to +125 Unit V V V V V V mA mW C C
3
R1282D002A
ELECTRICAL CHARACTERISTICS
Topt=25C
Symbol VIN VREFOUT IROUT
Item Operating Input Voltage VREFOUT Voltage Tolerance VREFOUT Output Current
Conditions VIN=3.3V, IOUT=1mA VIN=3.3V 2.5V < VIN < 5.5V = = 1mA < IROUT < 10mA VIN=3.3V = = VIN=3.3V, VREFOUT=0V -40C
< =
Min. 2.5 1.478 20
Typ. 1.500 2 6 25 150
Max. 5.5 1.522 6 12
Unit V V mA mV mV mA ppm/C
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 VUVLO VDTC10 VDTC1100 VDTC20 VDTC2100 AV1 FT1 VICR1 IAMPL IAMPH AV2 FT2 VICR2 VFB2 Oscillator Frequency 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 UVLO Released Voltage CH1 Duty=0% CH1 Duty=100% CH2 Duty=0% CH2 Duty=100% CH1 Open Loop Gain CH1 Single Gain Frequency Band CH1 Input Voltage Range CH1 Sink Current CH1 Source Current CH2 Open Loop Gain CH2 Single Gain Frequency Band CH2 Input Voltage Range CH2 Reference Voltage
Topt
< =
85C 0.985
VIN=3.3V -40C -40C
< = < =
1.000 150 150
1.015
V ppm/C ppm/C
Topt Topt
< = < =
85C 85C
-0.1
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=1.1V0V
0.1 700 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 1.9 0.7 to VIN 805 3.0 8.0 5.0 8.0 8.0 140 2.35 2.48 0.3 1.3 0.3 1.3
A kHz mA ms V V V V V V dB MHz V A
595
60 2.10
VIN=3.3V VIN=3.3V VIN=3.3V VIN=3.3V VIN=3.3V VIN=3.3V, AV1=0dB VIN=3.3V VIN=3.3V, VAMPOUT1=1.0V,VFB1=VFB1+ 0.1V VIN=3.3V, VAMPOUT1=1.0V,VFB1=VFB1- 0.1V VIN=3.3V VIN=3.3V, AV2=0dB VIN=3.3V VIN=3.3V
0.1 1.1 0.1 1.1
70
115
-1.4 -0.7
mA dB kHz V
60 600
-0.2 to VIN-1.3 1.000
0.985
1.015
V
4
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.

i2 Inductor VIN i1 GND Lx Tr CL Diode IOUT VOUT
Discontinuous Mode
IL ILxmax ILxmin ILxmin Tf Iconst t Ton T=1/fosc Toff Ton T=1/fosc Toff t IL
Continuous Mode
ILxmax
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 x 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 x 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)xt/L, therefore electric power, POFF is described as in next formula.
POFF =
Tf 0
VIN x (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) x {
Ton 0
VIN2 x t/L dt +
Tf 0
VIN x (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. VINxTon/L=(VOUT-VIN)xToff/L ..........................................................................................Formula 4 Further, the electric power, PAV is equal to output electric power, VOUTxIOUT, thus, IOUT = fOSC x VIN2xTon2/{2xL x(VOUT-VIN)}=VIN2xTon/(2xLxVOUT)......................................Formula 5 When IOUT becomes more than VINxTonxToff/(2xLx(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 = fOSCxVIN2 xTon2/(2xLx(VOUT-VIN))+VINxIconst/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 +VINxTon/L........................................................................................... Formula 7 With the formula 4,6, and ILXmax is, ILXmax = VOUT/VINxIOUT+VINxTon/(2xL)........................................................................... 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:
IL
Lx Tr i1 Inductor IOUT VOUT CL
ILxmax
VIN SD
ILxmin topen t
i2
Ton T=1/fosc
Toff
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 = VOUTxtopen / L = (VIN-VOUT) xton/LEquation A wherein, T=1/fosc=ton+toff duty (%)=ton/Tx100=tonx fosc x100 topen < toff = In Equation A, VOUTxtopen/L and (VIN-VOUT) xton/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=TxVOUT/VIN Equation B When ton8
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 ) xt/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 / (2L (Ton+Toff)).... Formula 10
This electric power PAV equals to output electric power VOUT x IOUT, thus, IOUT = VIN / VOUTx (VIN - VOUT )Ton2/(2xLx (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 ) xTon/L=VOUTxToff/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+VOUTxToff /(2xL)......................................................................................... Formula 13 In this moment, the peak current, ILXmax flowing through the inductor and the driver Tr. is described as follows: ILXmax= IOUT +VOUTxToff/(2xL)..................................................................................... 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
EXT1 C1 GND VIN Vrefout DTC1 VFB1 DTC2 VFB2 C2
OSCILLOSCOPE
EXT2 C1 GND VIN Vrefout DTC1 VFB1 DTC2 VFB2 C2 OSCILLOSCOPE
Test Circuit 1
Test Circuit 2
EXT1 C1 GND VIN Vrefout C2 DTC1 VFB1 DTC2 VFB2
OSCILLOSCOPE
EXT2 C1 GND VIN Vrefout C2 DTC1 VFB1 DTC2 VFB2 OSCILLOSCOPE
Test Circuit 3
Test Circuit 4
C1
GND
VIN Vrefout C2
C1
GND
VIN Vrefout C2
DTC1 VFB1
DTC2 VFB2
V
DTC1 VFB1
DTC2 VFB2
A V
Test Circuit 5
Test Circuit 6
10
R1282D002A
EXT1 C1 GND VIN Vrefout DTC1 VFB1 DTC2 VFB2 C2
OSCILLOSCOPE OSCILLOSCOPE
EXT1 C1 GND VIN Vrefout DTC1 VFB1 DTC2 VFB2 C2
Test Circuit 7
Test Circuit 8
EXT2 C1 GND VIN Vrefout C2 DTC1 VFB1 DTC2 VFB2 DTC1 VFB1 DTC2 VFB2 OSCILLOSCOPE C1 GND VIN AMPOUT1 Vrefout C2
A
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=4.7F, C2=1.0F Efficiency (%) can be calculated with the next formula: =(VOUT1xIOUT1+VOUT2xIOUT2)/(VINxIIN)x100
11
R1282D002A
TYPICAL CHARACTERISTICS
1) Output Voltage vs. Output Current (Topt=25C)
R1282D002A
10.10 L1=6.8H,C1=10F,VOUT2=2.5V,IOUT2=0mA 2.60
R1282D002A
L2=6.8H,C2=10F,VOUT1=10V,IOUT1=0mA
Output Voltage VOUT1(V)
10.05 10.00 9.95 9.90
Output Voltage VOUT1(V)
2.55 2.50 2.45 2.40
VIN=2.8V VIN=3.3V VIN=5.5V 0 50 100 150 Output Current IOUT1(mA) 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=25C)
R1282D002A
90 80 70 L1=6.8H,C1=10F,VOUT2=2.5V,IOUT2=0mA 90 80 70
R1282D002A
L2=6.8H,C2=10F,VOUT1=10V,IOUT1=0mA
Efficiency (%)
60 50 40 30 20 10 0 0 VOUT1=5V VOUT1=10V VOUT1=15V 50 100 150 Output Current IOUT(mA) 200
Efficiency (%)
60 50 40 30 20 10 0 0 VOUT2=1.8V VOUT2=2.5V 100 200 300 400 500 Output Current lOUT(mA) 600
3) Output Voltage vs. Temperature (VIN=3.3V)
R1282D002A
L1=6.8H,C1=10F 11.0 3.00
R1282D002A
L2=6.8H,C2=10F
Output Voltage VOUT1(V)
10.5 10.0 9.5 IOUT=10mA IOUT=100mA 9.0 -60 -40 -20 0 20 40 60 Temperature Topt(C) 80 100
Output Voltage VOUT2(V)
2.75 2.50 2.25
IOUT=10mA IOUT=100mA IOUT=200mA 80 100
2.00 -60 -40 -20 0 20 40 60 Temperature Topt(C)
12
R1282D002A
4) Frequency vs. Temperature
R1282D002A
Oscillator Frequency fosc(kHz)
800 750 700 650 600 VIN=2.5V VIN=3.3V VIN=5.5V
550 -60 -40 -20 0 20 40 60 80 100 Temperature Topt(C)
5) Feedback Voltage vs. Temperature (VIN=3.3V)
R1282D002A
1.02
Feedback Voltage VFB1(V)
R1282D002A
1.02
1.01 1.00 0.99 0.98 0.97 -60 -40 -20 0 20 40 60 80 100 Temperature Topt(C)
Feedback Voltage VFB2(V)
1.01 1.00 0.99 0.98 0.97 -60 -40 -20 0 20 40 60 80 Temperature Topt(C) 100
6) Vrefout Voltage vs. Temperature(VIN=3.3V)
R1282D002A
1.55
Vrefout Voltage (V)
7) Vrefout Output Voltage vs. Output Current
R1282D002A
1.8 1.6
Vrefout Voltage (V)
1.53 1.51 1.49 1.47 1.45 -60 -40 -20 0 20 40 Temp(C) 60 80 100
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 VIN=2.5V
VIN=3.3V
VIN=5.5V
10 20 30 40 50 60 70 Vrefout Output Current(mA)
80
13
R1282D002A
8) Vrefout Output Voltage vs. Output Current
R1282D002A
1.508 1.506 1.504 1.502 1.500 1.498 0 5 10 15 Vrefout Output Current(mA) 20 VIN=3.3V VIN=2.5V VIN=5.5V 1.510
9) Protection Delay Time vs. Temperature (VIN=3.3V)
R1282D002A
Porotection Delay Time TDLY (ms)
140 120 100 80 60 -60 -40 -20 0 20 40 60 Temperature Topt(C)
Vrefout Voltage (V)
80 100
10) Maximum Duty Cycle vs. DTC Voltage (VIN=3.3V)
R1282D002A
CH1 Maximum Duty Cycle Duty1 (%) CH2 Maximum Duty Cycle Duty2 (%)
100 80 60 40 20 0 0.0 100 80 60 40 20 0 0.0
R1282D002A
0.2
0.4 0.6 0.8 1.0 DTC1 Voltage(V)
1.2
1.4
0.2
0.4 0.6 0.8 1.0 DTC2 Voltage(V)
1.2
1.4
11) Output Sink Current vs. Temperature (VIN=3.3V)
R1282D002A
Output Sink Current IAMPL (A)
130 120 110 100 90 -60 -40 -20 0 20 40 60 80 100 Temperature Topt(C)
12) Output Source Current vs. Temperature
R1282D002A
Output Source Current IAMPH (A)
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)
14
R1282D002A
13) Load Transient Response (Step-up Side) VIN=3.3V, L1=6.8H
R1282D002A
10.5 0.30 11.5
R1282D002A
0.30 0.25 0.20 0.15 0.10 0.05
Output Voltage VOUT1(V)
Output Current IOUT(A)
9.5 9.0 8.5 8.0 7.5 0.0000 0.0005 0.0010 0.0015 Time (s)
10.5 10.0 9.5 9.0 8.5 0.00 0.01 0.02 Time (s) 0.03
0.20 0.15 0.10 0.05 0.00 0.04
0.00 0.0020
14) Load Transient Response (Step-down Side) VIN=3.3V, L2=6.8H
R1282D002A
3.00 0.30
3.00
R1280D002A
0.30
Output Voltage VOUT2(V)
Output Voltage VOUT2(V)
Output Current IOUT(A)
2.50 2.25 2.00 1.75 1.50 0.0000 0.0005 0.0010 0.0015 Time (s)
0.20 0.15 0.10 0.05 0.00 0.0020
2.50 2.25 2.00 1.75 1.50 0.00 0.01 0.02 Time (s) 0.03
0.20 0.15 0.10 0.05 0.00 0.04
Output Current IOUT(A)
2.75
0.25
2.75
0.25
Output Current IOUT(A)
10.0
Output Voltage VOUT1(V)
11.0
0.25
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R1282D002A
TYPICAL APPLICATION AND TECHNICAL NOTES
VOUT1 C1 Diode
L1
C3 EXT1 NMOS EXT2 VIN PMOS L2 GND AMPOUT1 Vrefout R7 DTC1 R8 VFB1 VFB2 DTC2 C5 R10 Diode C2 R6 R4 R9 C8 VOUT2
R1
C6 C9
C7
R3
R2
R5
R11 C4
Components examples Inductor L1,2 Diode PMOS NMOS
6.8H 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=47k R2=5.1k R3=30k R4=20k R5=43k R6=10kW R7=R9=22k R8=R10=43k R11=220k Capacitors Ceramic Type C1=C2=10F C3=4.7F C7=50pF C8=1F
C4=0.22F C9=1000pF
C5=0.47F
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.
16
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=VFB1x(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=VFB2x(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. TSS1RO1xC4 If R10=0, then, TSS2R9xC5xln((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) xVrefout-0.2)/(1.2-0.2) x100 (%) 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 4.7F. * 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 10k to 50k as R5 and try to reduce the noise level. In the case of VOUT2, 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, 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 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 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.
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