12345 `99.12.8 Step-down DC/DC Converter with Voltage Detector R1221N Series n OUTLINE The R1221N Series are PWM step-down DC/DC Converter controllers embedded with a voltage detector, with low supply current by CMOS process. Each step-down DC/DC converter in these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, and resistors for voltage detection. A low ripple, high efficiency step-down DC/DC converter can be composed of this IC with only four external components, or a power-transistor, an inductor, a diode and a capacitor. The output voltage of DC/DC converter can be supervised by the built-in voltage detector. With a PWM/VFM alternative circuit, when the load current is small, the operation turns into the VFM oscillator from PWM oscillator automatically, therefore the efficiency at small load current is improved. And the PWM/VFM alternative circuit is an option, in terms of C version and D version, the circuit is not included. If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. There are two types of protection function. One is latch-type protection circuit, and it works to latch an external Power MOS with keeping it disable. To release the condition of protection, after disable this IC with a chip enable circuit, enable it again, or restart this IC with power-on. The other 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. Either of these protection circuits can be designated by users' request. n FEATURES l Wide Range of Input Voltage * * * * * * * * * * * * * 2.3V to 13.2V l Built-in Soft-start Function and two choices of Protection Function(Latch-type or Reset-type) l Two choices of Oscillator Frequency * * * * * * * * * * 300kHz, 500kHz l High Efficiency * * * * * * * * * * * * * * * * * * * * * * TYP. 90% l Standby Current * * * * * * * * * * * * * * * * * * * * * TYP. 0A l Setting Output Voltage * * * * * * * * * * * * * * * * * Stepwise setting with a step of 0.1V in the range of 1.5V to 5.0V l High Accuracy Output Voltage * * * * * * * * * * * * * * 2.0% l Setting Detector Threshold Voltage * * * * * * * * * * * Stepwise setting with a step of 0.1V in the range of 1.2V to 4.5V l High Accuracy Detector Threshold Voltage* * * * * * * 2.0% l Low Temperature-Drift Coefficient of Output Voltage * TYP. 100ppm/C n APPLICATIONS l Power source for hand-held communication equipment, cameras, video instruments such as VCRs, camcorders. l Power source for battery-powered equipment. l Power source for household electrical appliances. 12345 Rev. 1.11 -1- n BLOCK DIAGRAM OSC VIN VOUT Vref EXT Protection PWM/VFM CONTROL Soft Start Chip Enable CE Vref VDOUT GND n SELECTION GUIDE In the R1221N Series, the output voltage, the detector threshold, 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 by designating the part number as shown below; R1221NXXXX-TR - -a bc Code a b c Contents Setting Output Voltage(VOUT): Stepwise setting with a step of 0.1V in the range of 1.5V to 5.0V is possible. Setting Detector Threshold(-VDET) Stepwise setting with a step of 0.1V in the range of 1.2V to 4.5V is possible. A:3.0V Designation of Oscillator Frequency and Optional Function A:300kHz, with a PWM/VFM alternative circuit, Latch-type protection B:500kHz, with a PWM/VFM alternative circuit, Latch-type protection C:300kHz, without a PWM/VFM alternative circuit, Latch-type protection D:500kHz, without a PWM/VFM alternative circuit, Latch-type protection E:300kHz, with a PWM/VFM alternative circuit, Reset-type protection F:500kHz, with a PWM/VFM alternative circuit, Reset-type protection G:300kHz, without a PWM/VFM alternative circuit, Reset-type protection H:500kHz, without a PWM/VFM alternative circuit, Reset-type protection 12345 Rev. 1.11 -2- n PIN CONFIGURATION l SOT-23-6W 5 6 4 VOUT GND CE (mark side) EXT VDOUT VIN 1 3 2 n PIN DESCRIPTION Pin No. Symbol 1 EXT 2 VDOUT 3 VIN Power Supply Pin 4 CE Chip Enable Pin 5 GND Ground Pin 6 VOUT Pin for Monitoring Output Voltage Description External Transistor Drive Pin (Output Type ; CMOS) Voltage Detector Output Pin (Output Type ; Nch Open Drain ) n ABSOLUTE MAXIMUM RATING Symbol VIN Item VIN Supply Voltage Rating Unit 15 V VEXT EXT Pin Output Voltage -0.3~VIN+0.3 V VCE CE Pin Input Voltage -0.3~VIN+0.3 V -0.3~15 V -0.3~VIN+0.3 V VDOUT VDOUT Pin Output Voltage VOUT VOUT Pin Input Voltage IEXT EXT Pin Inductor Drive Output Current 25 mA PD Power Dissipation 250 mW Topt Operating Temperature Range -40~+85 C Tstg Storage Temperature Range -55~+125 C 12345 Rev. 1.11 -3- n ELECTRICAL CHARACTERISTICS lR1221N***A(C,E,G) Output Voltage : Vo, Detector Threshold : VD Symbol VIN Item Conditions Operating Input Voltage VOUT Step-down Output Voltage (Topt=25C) MIN. TYP. MAX. Note* Unit 2.3 VIN=VCE=Vo+1.2V, IOUT=-10mA Vo 13.2 Vo 0.98 DVOUT/ DT Step-down Output Voltage -40C Topt 85C Vo V A 1.02 100 ppm/ C Temperature Coefficient fosc Oscillator Frequency DfOSC/ Frequency Temperature DT VIN=VCE=Vo+1.2V, IOUT=-100mA 240 -40C Topt 85C 300 360 A 0.3 C IDD1 Supply Current1 VIN=13.2V,VCE=13.2V,VOUT=13.2V Istb Standby Current VIN=13.2V,VCE=0V,VOUT=0V IEXTH EXT "H" Output Current VIN=8V,VEXT=7.9V,VOUT=8V,VCE=8V IEXTL EXT "L" Output Current VIN=8V,VEXT=0.1V,VOUT=0V,VCE=0V ICEH CE "H" Input Current VIN=13.2V,VCE=13.2V,VOUT=13.2V ICEL CE "L" Input Current VIN=13.2V,VCE=0V,VOUT=13.2V VCEH CE "H" Input Voltage VIN=8V,VCE=0V(R)1.5V VCEL CE "L" Input Voltage VIN=8V,VCE=1.5V(R)0V Maxdty Oscillator Maximum Duty Cycle VFMdty VFM Duty Cycle Applied to B and F versions only Delay Time by Soft-Start VIN=Vo+1.2V,VCE=0V(R)Vo+1.2V function At 80% of rising 10 100 160 B mA 0 0.5 C mA -10 -6 D mA D mA E mA E mA F V F V 20 0 -0.5 0.8 0.3 100 % 25 10 16 F ms 1 3 5 G ms 0.5 I mA I mA J V VDOUT Output Leakage Current VIN=VOUT=VCE=VDOUT=8V 0 IVDL VDOUT "L" Output Current VIN=VOUT=2.3V, VCE=0V, VDOUT=0.1V 0.5 1 Detector Threshold VIN=6V, VCE=6V, VOUT=VD1.2V(R)0V VD VD 0.98 Output Delay Time for Released VIN=6V, VCE=6V, VOUT=0V(R)VD1.2V D-VDET/ Voltage At 80% of rising Detector Threshold Hysteresis VIN=6V, VCE=6V, VOUT=0V(R)VD1.2V Detector Threshold -40C Topt 85C DT Temperature Coefficient Note: Refer to Test Circuits VD 1.02 2 5 10 J ms VD VD VD J mV 0.01 0.03 0.05 100 ppm/ C 12345 Rev. 1.11 % 5 IVDLK VHYS 1.2 0.8 Delay Time for protection circuit VIN=Vo+1.2V,VCE=Vo+1.2V(R)0V tVDET 0.5 0 Tprot -VDET kHz %/ Coefficient Tstart V -4- lR1221N***B(D,F,H) Output Voltage : Vo, Detector Threshold : VD Symbol VIN VOUT Item Conditions Operating Input Voltage Step-down Output Voltage (Topt=25C) MIN. TYP. MAX. Note* Unit 2.3 VIN=VCE=Vo+1.2V, IOUT=-10mA Vo 13.2 Vo Vo 0.98 DVOUT/ DT fosc DfOSC/ DT Step-down Output Voltage -40C Topt 85C Oscillator Frequency Frequency Temperature VIN=VCE=Vo+1.2V, IOUT=-100mA 1.02 100 400 -40C Topt 85C 500 600 Standby Current VIN=13.2V,VCE=0V,VOUT=0V IEXTH EXT "H" Output Current VIN=8V,VEXT=7.9V,VOUT=8V,VCE=8V IEXTL EXT "L" Output Current VIN=8V,VEXT=0.1V,VOUT=0V,VCE=0V ICEH CE "H" Input Current VIN=13.2V,VCE=13.2V,VOUT=13.2V ICEL CE "L" Input Current VIN=13.2V,VCE=0V,VOUT=13.2V VCEH CE "H" Input Voltage VIN=8V,VCE=0V(R)1.5V VCEL CE "L" Input Voltage VIN=8V,VCE=1.5V(R)0V Maxdty Oscillator Maximum Duty Cycle VFMdty VFM Duty Cycle Applied to B and F versions only Delay Time by Soft-Start VIN=Vo+1.2V,VCE=0V(R)Vo+1.2V function At 80% of rising 0.3 %/ 10 200 B mA 0 0.5 C mA -10 -6 D mA D mA E mA E mA F V F V 20 0 -0.5 0.5 0 0.8 0.3 1.2 0.8 100 % 25 % 3 6 10 F ms 1 2 4 G ms 0 0.5 I mA I mA J V Delay Time for protection circuit VIN=Vo+1.2V,VCE=Vo+1.2V(R)0V IVDLK VDOUT Output Leakage Current VIN=VOUT=VCE=VDOUT=8V IVDL VDOUT "L" Output Current VIN=VOUT=2.3V,VCE=0V, VDOUT=0.1V 0.5 1 Detector Threshold VIN=6V, VCE=6V, VOUT=VD1.2V(R)0V VD VD VD 0.98 Output Delay Time for Released VIN=6V, VCE=6V, VOUT=0V(R)VD1.2V Voltage At 80% of rising Detector Threshold Hysteresis VIN=6V, VCE=6V, VOUT=0V(R)VD1.2V Detector Threshold -40C Topt 85C 1.02 1.5 3.5 6.0 J ms VD VD VD J mV 0.01 0.03 0.05 100 DT Temperature Coefficient Note: Refer to Test Circuits ppm/ C 12345 Rev. 1.11 kHz 140 Tprot D-VDET/ A C Istb VHYS ppm/ Coefficient VIN=13.2V,VCE=13.2V,VOUT=13.2V tVDET V C Supply Current1 -VDET A Temperature Coefficient IDD1 Tstart V -5- n TEST CIRCUITS A) F) L PMOS L PMOS + 3 1 + 6 SD -- VIN 4 - V CL + 5 2 CIN 3 - CIN VIN SD 4 - V CL 5 2 OSCILLOSCOPE B) 3 A VIN + 6 1 1 OSCILLOSCOPE 6 G) + - OSCILLOSCOPE 4 2 5 CIN 3 1 6 4 2 5 3 1 6 VOUT VIN C) 3 A 1 6 H) VIN 2 4 A 5 VOUT VIN D) 4 A 2 5 VEXT I) 3 1 6 VIN 5 2 1 6 4 2 5 VIN VOUT 4 3 E) VDOUT A J) 3 1 6 3 1 4 2 6 VIN A 4 2 5 VOUT VIN R Inductor L : 27mH(Sumida Electronic, CD104) Capacitor CL: 47mF(Tantalum type) Power MOS PMOS : HAT1020R(Hitachi) OSCILLOSCOPE Diode SD : RB491D (Rohm, Schottky type) CIN : 22mF(Tantalum type) Resistor R : 100kW 12345 Rev. 1.11 5 -6- n TYPICAL APPLICATIONS AND APPLICATION HINTS PMOS L VIN CIN Vcc EXT VOUT R1 SD1 CE GND COUT Reset/ VDOUT CE CONTROL CPU PMOS: HAT1020R (Hitachi), Si3443DV (Siliconix) SD1 : RB491D (Rohm) CIN :10mF(Tantalum Type) L : CD105(Sumida, 27mH) COUT : 47mF(Tantalum Type) R1 : 100kW When you use these ICs, consider the following issues; l 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. l Detector threshold hysteresis is set at 3 percent of detector threshold voltage. (Min. 1 percent, Max. 5 percent) l Setting Detector threshold voltage range depends on Output voltage of DC/DC converter. Release Voltage from Reset condition must not be more than Output voltage of DC/DC converter. (Detector Threshold Voltage1.07 < Output Voltage of DC/DC converter0.98 l When the R1221NXXXX is on stand-by mode, the output voltage of VDOUT is GND level, therefore if the pull-up resistor for VDOUT pin is pulled up another power supply, a certain amount of current is loading through the resistor. l The operation of Latch-type protection circuit is as follows; When the maximum duty cycle continues longer than the delay time for protection circuit, (Refer to the Electrical Characteristics) the protection circuit works to shut-down the external Power MOS with its latching operation. Therefore when an input/output voltage difference is small, the protection circuit may work even at small load current. To release the protection state, after disable this IC with a chip enable circuit, enable it again, or restart this IC with power-on. However, in the case of restarting this IC with power-on, after the power supply is turned off, if a certain amount of charge remains in CIN, or some voltage is forced to VIN from CIN, this IC might not be restarted even after power-on. If rising transition speed of supply voltage is too slow, or the time which is required for VIN voltage to reach Output Voltage of DC/DC converter is longer than soft-starting time plus delay time for protection circuit, protection circuit works before VIN voltage reaches Output Voltage of DC/DC converter. To avoid this condition, make this IC disable(CE="L") first, then force VIN voltage, and after VIN voltage becomes equal or more than VOUT, make this IC enable(CE="H"). l 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 flows through the connection of power supply, an inductor and the connection of VOUT. If the impedance of power supply line is high, the voltage level of power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC. 12345 Rev. 1.11 -7- l Use capacitors with a capacity of 22mF or more for VOUT Pin, and with good high frequency characteristics such as tantalum capacitors. We recommend you to use capacitors with an allowable voltage which is 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. l 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. l Use a diode of a Schottky type with high switching speed, and also pay attention to its current capacity. l Do not use this IC under the condition at VIN voltage less than minimum operating voltage. P 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. n 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 ILmax IOUT ILmin L VIN Lx Tr SD topen VOUT i2 CL ton toff T=1/fosc Step 1 : LxTr 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 LXTr. Step 2 : When LxTr 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), sith the oscillator frequency(fosc) being maintained constant. l Discontinuous Conduction Mode and Continuous Conduction Mode 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 when it is OFF. The difference between ILmax and ILmin, which is represented by DI ; DI =ILmax -ILmin =VOUTtopen/L=(VIN-VOUT)ton/LxxxEquation 1 wherein T=1/fosc=ton+toff duty(%)=ton/T100=tonfosc100 topentoff 12345 Rev. 1.11 -8- In Equation 1, VOUTtopen/L and (VIN-VOUT)ton/L are respectively show the change of the current at ON, and the change of the current at OFF. When the output current(IOUT) is relatively small, topen0). 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 =TVIN/VOUTxxx Equation 2 When ton