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s OUTLINE
PRELIMINARY
2001.10.18
PWM/VFM step-down DC/DC Converter
R1224N Series
The R1224N Series are CMOS-based PWM step-down DC/DC Converter controllers with low supply current. Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a phase compensation circuit, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, resistors for output voltage detect, and input voltage detect circuit. A low ripple, high efficiency step-down DC/DC converter can be easily composed of this IC with only several external components, or a power-transistor, an inductor, a diode and capacitors. Output Voltage is fixed or can be adjusted with external resistors (Adjustable types are without PWM/VFM alternative circuit). With a PWM/VFM alternative circuit, when the load current is small, the operation is automatically switching into the VFM oscillator from PWM oscillator. Therefore, the efficiency at small load current is improved. Several types of the R1224N XXX, which are without a PWM/VFM alternative circuit, are also available. If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. The protection circuit is Reset-type protection circuit, and it works to restart the operation with soft-start and repeat this operation until maximum duty cycle condition is released. When the cause of large load current or something else is removed, the operation is automatically released and returns to normal operation. Further, built-in UVLO function works when the input voltage is equal or less than UVLO threshold, it makes this IC be standby and suppresses the consumption current and avoid an unstable operation.
s FEATURES
q Range of Input Voltage * * * * * * * * * * * * *2.3V18.5V q Built-in Soft-start Function and Protection Function (Reset type protection) q Three options of Oscillator Frequency * * * * * *180kHz, 300kHz, 500kHz q High Efficiency * * * * * * * * * * * * * * * * * *TYP. 90% q Output Voltage * * * * * * * * * * * * * Stepwise Setting with a step of 0.1V in the range of 1.2V to 6.0V as fixed voltage type. Reference Voltage of Adjustable Type is 1.0V q Standby Current * * * * * * * * * * * * * * * * *TYP. 0.0A q High Accuracy Output Voltage * * * * * * * * * *2.0% q Low Temperature-Drift Coefficient of Output Voltage * * * * * TYP. 100ppm/C
s APPLICATIONS
q Power source for hand-held communication equipment, cameras, video instruments such as VCRs, camcorders. q Power source for battery-powered equipment. q Power source for household electrical appliances.
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Rev. 0.06 -1-
s BLOCK DIAGRAM
*Fixed Output Voltage Type
VIN
OSC
VOUT
Amp
Vref
Soft Start Chip Enable
EXT
PWM/VFM CONTROL Protection
CE
UVLO
Vref
GND
*Adjustable Output Voltage Type
VIN
OSC
VFB
Amp
Vref
Soft Start
EXT
PWM/VFM CONTROL Protection
Chip Enable
CE
UVLO
Vref
GND
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Rev. 0.06 -2-
s SELECTION GUIDE
In the R1224N Series, the output voltage, the oscillator frequency, the optional function, and the taping type for the ICs can be selected at the user's request. The selection can be made with designating the part number as shown below;
R1224NXX2X-XX
a bc
Code a
d
b c
d
Contents Setting Output Voltage(VOUT): Stepwise setting with a step of 0.1V in the range of 1.2V to 6.0V is possible. Adjustable type; a=10 means Reference voltage=1.0V Optional Function is G/H/M. Designation of Oscillator Frequency 2 : fixed Designation of Optional Function E : 300kHz, with a PWM/VFM alternative circuit F : 500kHz, with a PWM/VFM alternative circuit G : 300kHz, without a PWM/VFM alternative circuit H : 500kHz, without a PWM/VFM alternative circuit L : 180kHz, with a PWM/VFM alternative circuit M : 180kHz, without a PWM/VFM alternative circuit Designation of Taping Type; Ex. :TR,TL(refer to Taping Specification) "TR" is prescribed as a standard.
s PIN CONFIGURATION
q SOT-23-5
5
4
VIN EXT (mark side) VOUT CE GND (VFB)
1
2
3
s PIN DESCRIPTION
Pin No. 1 2 3 4 5 Symbol CE GND VOUT /(VFB) EXT VIN Description Chip Enable Pin (Active with "H") Ground Pin Pin for Monitoring Output Voltage(Feedback Voltage) External Transistor Drive Pin(CMOS Output) Power Supply Pin
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Rev. 0.06 -3-
s ABSOLUTE MAXIMUM RATINGS
(GND=0V) Symbol VIN VEXT VCE VOUT/(VFB) IEXT PD Topt Tstg Item VIN Supply Voltage EXT Pin Output Voltage CE Pin Input Voltage VOUT/VFB Pin Input Voltage EXT Pin Inductor Drive Output Current Power Dissipation Operating Temperature Range Storage Temperature Range Rating 20 -0.3VIN+0.3 -0.3VIN+0.3 -0.3VIN+0.3 50 250 -40+85 -55+125 Unit V V V V mA mW C C
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Rev. 0.06 -4-
s ELECTRICAL CHARACTERISTICS
qR1224Nxx2X (X=E/F/G/H/L/M) except R1224N102X Symbol VIN VOUT VOUT/ T fosc Item Operating Input Voltage Step-down Output Voltage VIN=VCE+VSET+1.5V, IOUT=-100mA When VSET2.0, then VIN=VCE=3.5V Step-down Output Voltage Temperature Coefficient Oscillator Frequency VIN=VCE=VSET+1.5V, IOUT=-100mA When VSET2.0, then VIN=VCE=3.5V L/M version E/G version F/H version fOSC/ T IDD1 Oscillator Frequency Temperature Coefficient Supply Current1 VIN=VCE=VOUT=18.5V E/F/L/M version G version H version Istb IEXTH IEXTL ICEH ICEL VCEH VCEL Maxdty VFMdty VUVLO1 VUVLO2 Standby Current EXT "H" Output Current EXT "L" Output Current CE "H" Input Current CE "L" Input Current CE "H" Input Voltage CE "L" Input Voltage Oscillator Maximum Duty Cycle VFM Duty Cycle UVLO Voltage UVLO Release Voltage E/F/L version VIN=VCE=2.5V to 1.5V, VOUT=0V VIN=VCE=1.5V to 2.5V, VOUT=0V 1.9 VIN=18.5V, VCE=0V, VOUT=0V VIN=8V,VEXT=7.9V,VOUT=8V,VCE=8V VIN=8V,VEXT=0.1V,VOUT=0V,VCE=8V VIN=VCE=VOUT=18.5V VIN= VOUT=18.5V, VCE=0V VIN=8V,VOUT=0V VIN=8V,VOUT=0V 100 35 2.0 VUVLO1 +0.1 Tstart
Delay Time by Soft-Start function
(Topt=25C) Conditions MIN. 2.3 VSETx 0.98 100 VSET TYP. MAX. Unit 18.5 VSETx 1.02 ppm /C kHz 144 240 400 180 300 500 0.2 216 360 600 % /C A 20 30 40 0.0 -17 30 0.0 -0.5 1.5 0.3 0.0 0.5 50 70 90 0.5 A mA mA A A V V % % 2.2 2.3 V V V V
-40C Topt 85C
-40C Topt 85C
VIN=VSET+1.5V, IOUT=-10mA VCE=0V->VSET+1.5V
10
ms
Tprot
Delay Time for protection circuit
VIN=VCE=VSET+1.5V VOUT=VSET+1.5V->0V
15
ms
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Rev. 0.06 -5-
qR1224N102X (X=G/H/M) Symbol VIN VFB VFB/ T fosc Item Operating Input Voltage Feedback Voltage Feedback Voltage Temperature Coefficient Oscillator Frequency VIN=VCE=3.5V, IFB=-100mA M version G version H version fOSC/ T IDD1 Oscillator Frequency Temperature Coefficient Supply Current1 VIN=VCE=VFB=18.5V M version G version H version Istb IEXTH IEXTL ICEH ICEL VCEH VCEL Maxdty VUVLO1 VUVLO2 Standby Current EXT "H" Output Current EXT "L" Output Current CE "H" Input Current CE "L" Input Current CE "H" Input Voltage CE "L" Input Voltage Oscillator Maximum Duty Cycle UVLO Voltage UVLO Release Voltage VIN=VCE=2.5V to 1.5V, VFB=0V VIN=VCE=1.5V to 2.5V, VFB=0V VIN=18.5V, VCE=0V, VFB=0V VIN=8V,VEXT=7.9V,VFB=8V,VCE=8V VIN=8V,VEXT=0.1V,VFB=0V,VCE=8V VIN=VCE=VFB=18.5V VIN= VFB=18.5V, VCE=0V VIN=8V,VFB=0V VIN=8V,VFB=0V 100 1.9 -0.5 1.5 -40C Topt 85C 144 240 400 VIN=VCE=3.5V, IFB=-100mA -40C Topt 85C Conditions MIN. 2.3 0.98
(Topt=25C) TYP. MAX. Unit 18.5 1.00 100 1.02 V V ppm /C kHz 180 300 500 0.2 216 360 600 % /C A 20 30 40 0.0 -17 30 0.0 0.0 0.5 50 70 90 0.5 A mA mA A A V 0.3 V % 2.0 VUVLO1 +0.1 2.2 2.3 V V
Tstart
Delay Time by Soft-Start function
VIN=2.5V, IFB=-10mA VCE=0V->2.5V
10
ms
Tprot
Delay Time for protection circuit
VIN=VCE=2.5V VFB=2.5V->0V
15
ms
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Rev. 0.06 -6-
s TYPICAL APPLICATION AND APPLICATION HINTS
(1) Fixed Output Voltage Type(R1224Nxx2E/F/G/H/L/M except xx=10)
L
R1
C1 VIN CE C2 EXT
PMOS
VOUT SD
C3 LOAD
GND
CE CONTROL
PMOS: HAT1044M (Hitachi) L: CR105-270MC (Sumida, 27H) SD1: RB063L-30 (Rohm) C3: 47F (Tantalum Type) C1: 10F (Ceramic Type) C2: 0.1F (Ceramic Type) R1: 10 (2) Adjustable Output Type (R1224N102G/H/M) Example: Output Voltage=3.2V
L
R1
C1 VIN CE C2 EXT
PMOS R4 R3 VFB SD R2
C4
C3 LOAD
GND
CE CONTROL
PMOS: HAT1044M (Hitachi) L: CR105-270MC (Sumida, 27H) SD1: RB063L-30 (Rohm) C3: 47F (Tantalum Type) C1: 10F (Ceramic Type) C2: 0.1F (Ceramic Type) C4: 2200pF(Ceramic Type) R1: 10, R2=10k, R3=2.7k, R4=22k When you use these ICs, consider the following issues; q As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed for load current, therefore do not use it in such a way. When you control the CE pin by another power supply, do not make its "H" level more than the voltage level of VIN pin. q Set external components as close as possible to the IC and minimize the connection between the components and the IC. In particular, a capacitor should be connected to VOUT pin with the minimum connection. And make sufficient grounding and reinforce supplying. A large switching current could flow through the connection of power supply, an inductor and the connection of VOUT. If the impedance of the connection of power supply is high, the voltage level of power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC. q Protection circuit may work if the maximum duty cycle continue for the time defined in the electrical characteristics. Once after stopping the output voltage, output will restart with soft-start operation. If the difference between input voltage and output voltage is small, the protection circuit may work.
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Rev. 0.06 -7-
q Use capacitors with a capacity of 22F or more for VOUT pin, and with good high frequency characteristics such as tantalum capacitors. We recommend you to use output capacitors with an allowable voltage at least twice as much as setting output voltage. This is because there may be a case where a spike-shaped high voltage is generated by an inductor when an external transistor is on and off. q Choose an inductor that has sufficiently small D.C. resistance and large allowable current and is hard to reach magnetic saturation. And if the value of inductance of an inductor is extremely small, the ILX may exceed the absolute maximum rating at the maximum loading. Use an inductor with appropriate inductance. q Use a diode of a Schottky type with high switching speed, and also pay attention to its current capacity. q Do not use this IC under the condition with VIN voltage at equal or less than minimum operating voltage. The performance of power source circuits using these ICs extremely depends upon the peripheral circuits. Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in a way that the values such as voltage, current, and power of each component, PCB patterns and the IC do not exceed their respected rated values.
s How to Adjust Output Voltage and about Phase Compensation
As for Adjustable Output type, feedback pin (VFB) voltage is controlled to maintain 1.0V. Output Voltage, VOUT is as following equation: VOUT: R2+R4=VFB: R2 VOUT=VFBx(R2+R4)/R2 Thus, with changing the value of R2 and R4, output voltage can be set in the specified range. In the DC/DC converter, with the load current and external components such as L and C, phase might be behind 180 degree. In this case, the phase margin of the system will be less and stability will be worse. To prevent this, phase margin should be secured with proceeding the phase. A pole is formed with external components L and C3. Fpole 1/2LxC3 A zero (signal back to zero) is formed with R4 and C4. Fzero1/(2xR4xC4) For example, if L=27H, C3=47F, the cut off frequency of the pole is approximately 4.5kHz. To make the cut off frequency of the pole as much as 4.5kHz, set R4=33k and C4=1000pF. If VOUT is set at 2.5V, R2=22k is appropriate. R3 prevents feedback of the noise to VFB pin, about 2.7k is appropriate value.
L
R1
C1 VIN CE C2 EXT
PMOS R4 R3 VFB SD R2
C4
C3 LOAD
GND
CE CONTROL
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Rev. 0.06 -8-
s 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: i1 IOUT VIN Lx Tr SD L i2 CL ton 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. q 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 x topen / L = (VIN-VOUT)xton/LEquation 1 wherein, T=1/fosc=ton+toff duty (%)=ton/Tx100=tonx fosc x 100 topen toff In Equation 1, 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 1 is solved for ton and assumed that the solution is tonc, tonc=TxVOUT/VIN Equation 2 When ton ILmax ILmin topen
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Rev. 0.06 -9-
s OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS
When Lx Tr. is ON: (Wherein, Ripple Current P-P value is described as IRP, ON resistance of LX Tr. is described as Rp the direct current of the inductor is described as RL.) VIN=VOUT+(Rp+RL)xIOUT+LxIRP/ton Equation 3 When Lx Tr. is OFF: LxIRP/toff = VF+VOUT+RLxIOUT Equation 4 Put Equation 4 to Equation 3 and solve for ON duty, ton/(toff+ton)=DON, DON=(VOUT+VF+RLxIOUT)/(VIN+VF-RpxIOUT)Equation 5 Ripple Current is as follows; IRP=(VIN-VOUT-RpxIOUT-RLxIOUT)xDON/f/L ...Equation 6 Wherein, peak current that flows through L, Lx Tr., and SD is as follows; ILmax=IOUT+IRP/2...Equation 7 Consider ILmax, condition of input and output and select external components. 5The above explanation is directed to the calculation in an ideal case in continuous mode.
s External Components
1. Inductor Select an inductor that peak current does not exceed ILmax. If larger current than allowable current flows, magnetic saturation occurs and make transform efficiency worse. When the load current is definite, the smaller value of L, the larger the ripple current. Provided that the allowable current is large in that case and DC current is small, therefore, for large output current, efficiency is better than using an inductor with a large value of L and vice versa. 2. Diode Use a diode with low VF (Schottky type is recommended.) and high switching speed. Reverse voltage rating should be more than VIN and current rating should be equal or more than ILmax. 3. Capacitors As for CIN, use a capacitor with low ESR (Equivalent Series Resistance) and a capacity of at least 10F for stable operation. COUT can reduce ripple of Output Voltage, therefore 47F or more value of tantalum type capacitor is recommended. 4. Lx Transistor Pch Power MOSFET is required for this IC. Its breakdown voltage between gate and source should be a few V higher than Input Voltage. In the case of Input Voltage is low, to turn on MOSFET completely, to use a MOSFET with low threshold voltage is effective. If a large load current is necessary for your application and important, choose a MOSFET with low ON resistance for good efficiency. If a small load current is mainly necessary for your application, choose a MOSFET with low gate capacity for good efficiency. Maximum continuous drain current of MOSFET should be larger than peak current, ILmax.
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Rev. 0.06 - 10 -
s TEST CIRCUITS
A) Output Voltage, Oscillator Frequency, CE"H" Input Voltage, CE"L" Input Voltage, Soft-start time
L1 PM O S
EXT
O scilloscope D1 + C1
VIN
G ND VO UT (VFB) CE
+ C2
V
-
B) Supply Current1
C) Standby Current
EXT
EXT GND VOUT (VFB) CE VIN
VIN
A
A
GND VOUT (VFB) CE
D) EXT "H" Output Current
E) EXT "L" Output Current
EXT
EXT VIN
VIN
A
GND VOUT (VFB) CE
A
GND VOUT (VFB) CE
F) CE "H" Input Current, CE "L" Input Current
G) Output Delay Time for Protection Circuit
EXT Oscilloscope GND VOUT (VFB) CE + C2 VIN
EXT GND VOUT (VFB)
VIN
CE
A
PMOS: HAT1044M (Hitachi) L: CD104-270MC (Sumida, 27H) SD1: RB491D (Rohm) C1: 47F (Tantalum Type) C2: 47F (Tantalum Type)
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Rev. 0.06 - 11 -

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