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RT9202Typical Application CircuitR120KR410D187SHDNH: shutdownQ22N700265C41µFPHASEOCSETFBVCCBOOTUGATEGNDLGATER31201234C20.1µFMUVOUT2.5V+C3L25µHMLC51µF+C1470µFMA732 5VRT92021000µFR2255C610nFFig.1 RT9202 powered from 5V onlyR412VR120K105VH: shutdownQ12N70028765C41µFPHASEOCSETFBVCCBOOT1UGATEGND23C21µFMUVOUT2.5V+C3L15µHMLC51µF+C1470µFSHDNRT9202LGATE4R3120R2250C610nF1000µFFig.2 RT9202 powered from 12Vwww.richtek.com
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DS9202-02 August 2002
RT9202MU+COUT1000µFDL5µHGSCIN11µF+CIN2470µFCVCC1µFGNDVCCBOOTCBOOTMLDGSGND ReturnRT92020.1µFLayout PlacementLayout Notes1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes.2. Put RT9202 to be near the COUT3. Put CBOOT as close as to BOOT pin4. Put CVCC as close as to VCC pinDS9202-02 August 2002www.richtek.com
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RT9202Function Block DiagramVCCPower onReset6.0VRegulatorBiasBOOT40µA0.8VReferenceSoft StartOC__1VOVPOCSET+UGATE+0.5V0.8VError35dB+_+UVPControlLogicPWMPHASEVCCLGATE+GND300kHzOscillatorwww.richtek.com
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__FBErrorAmpDS9202-02 August 2002
RT9202
Absolute Maximum Ratings
Supply Voltage VCC 7Vz BOOT & UGATE to GND 15Vz Input, Output or I/O VoltageGND−0.3V ~ 7Vz Power Dissipation, PD @ TA = 25°CSOP-80.625Wz Package Thermal ResistanceSOP-8, θJA160°C/Wz Ambient Temperature Range0°C ~ +70°Cz Junction Temperature Range-40°C ~ +125°Cz Storage Temperature Range-65°C ~ +150°Cz Lead Temperature (Soldering, 10 sec.)260°CCAUTION:
Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to thedevice. This is a stress only rating and operation of the device at these or any other conditions above thoseindicated in the operational sections of this specification is not implied.
z
Electrical Characteristics
(VCC = 5V, TA = 25°C, Unless otherwise specified.)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
VCC Supply Current / Regulated VoltageNominal Supply CurrentRegulated Voltage from BOOTPower-On ResetRising VCC ThresholdVCC Threshold HysteresisRising VOCSET ThresholdReferenceReference VoltageOscillator
Free Running FrequencyRamp AmplitudeError AmplifierDC gain
PWM Controller Gate DriverUpper Drive SourceUpper Drive SinkLower Drive SourceLower Drive Sink
RUGATERUGATERLGATERLGATE
BOOT= 12V
BOOT-VUGATE = 1VVUGATE = 1VVCC - VLGATE = 1V,VLGATE = 1V
--------7542
117.564
ΩΩΩ
32
35
38
dB
∆ VOSC
250--3001.75
350--KHzVP-P
0.784
0.8
0.816
V
VOCSET = 4.5VVOCSET1 = 4.5V
3.850.30.8
4.10.51.25
4.350.72.0
VVV
ICCVCC
UGATE, LGATE openVBOOT = 12V
--5
36
67
mAV
Ω
To be continued
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DS9202-02 August 2002
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RT9202ParameterProtectionFB Over-Voltage TripFB Under-Voltage TripOCSET Current SourceSoft-Start IntervalIOCSETFB RisingFB FallingVOCSET= 4.5V1.0--3511.10.5402--0.6454VVµAmSSymbolTest ConditionsMinTypMaxUnitsFunctional Pin DescriptionBOOT (Pin 1)This pin provides ground referenced bias voltage to theupper MOSFET driver. A bootstrap circuit is used tocreate a voltage suitable to drive a logic-level N-channel MOSFET when operating at a single 5V powersupply. This pin also could be powered from ATX 12V,in this situation, a internal 6.0V regulator will supply toVCC pin for internal voltage bias.UGATE (Pin 2)Connect UGATE pin to the PWM converter’s upperMOSFET gate. This pin provides the gate drive for theupper MOSFET.GND (Pin 3)Signal and power ground for the IC. All voltage levelsare measured with respect to this pin.LGATE (Pin 4)Connect LGATE to the PWM converter’s lowerMOSFET gate. This pin provides the gate drive for thelower MOSFET.VCC (Pin 5)This is the main bias supply for the RT9202. This pinalso provides the gate bias charge for the lowerMOSFETs gate. The voltage at this pin monitored forpower-on reset (POR) purpose. This pin is also theinternal 6.0V regulator output powered from BOOT pinwhen BOOT pin is directly powered from ATX 12V.FB (Pin 6)This pin is connected to the PWM converter’s outputdivider. This pin also connects to internal PWM erroramplifier inverting input and protection monitor.OCSET (Pin 7)Connect a resistor from this pin to the drain of therespective upper MOSFET. This resistor, an internal40µA current source, and the upper MOSFET on-resistance set the converter over-current trip point. Anover-current trip cycles the soft-start function. Thevoltage at this pin is monitored for power-on reset(POR) purpose and pulling this pin low with an opendrain device will shut down the IC.IPEAK=IOCSET×ROCSETRDS(ON)PHASE (Pin 8)This pin is used to monitor the voltage drop across theupper MOSFET for over-current protection.www.richtek.com
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DS9202-02 August 2002
RT9202
Typical Operating Charateristics
Dead Time
VCC = 5V
UGATE
UGATE
Dead Time
VCC = 5V
LGATELGATE
TimeTime
Power On
VCC = 5VVOUT = 2.2V
VCC
Power Off
VCC= 5VVOUT= 2.2V
VCC
VOUTVOUT
TimeTime
Load Transient
UGATE
Load Transient
UGATE
VCC = 5VVOUT = 2.2VCOUT = 3000µF
VOUT
VOUT
VCC = 5VVOUT = 2.2VCOUT = 3000µF
TimeTime
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RT9202Bootstrap Wave FormVCC = 5V; VOUT = 2.2VVCC = 5VVOUT = 2.2VVOUTShort HiccupUGATELGATEPHASEUGATETimeTimeReference vs. Temperature0.8030.8020.801555045IOCSET vs. TemperatureReference (V)0.8000.7990.7980.7970.796-50050100150IOCSET ( A)µ4035302520-40-10205080110140Temperature ( C)°Temperature ( C)°4.34.24.1POR (Rising/Falling) vs. Temperature315Oscillator Frequency vs. Temperature310305RisingFrequency (kHz)300295290285280275POR (V)4.03.93.8Falling3.73.6-50050100150270-50050100150Temperature ( C)°Temperature ( C)°www.richtek.com
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DS9202-02 August 2002
RT9202
Functional Description
The RT9202 operates at either single 5V powersupply with a bootstrap UGATE driver or 5V/12Vdual-power supply form the ATX SMPS. The dual-power supply is recommended for high currentapplication, the RT9202 can deliver higher gatedriving current while operating with ATX SMPS basedon dual-power supply.
The Bootstrap Operation
In a single power supply system, the UGATE driver ofRT9202 is powered by an external bootstrap circuit,as the Fig.1. The boot capacitor, CBOOT, generates afloating reference at the PHASE pin. Typically a0.1µF CBOOT is enough for most of MOSFETs usedwith the RT9202. The voltage drop between BOOTand PHASE is refreshed to a voltage of VCC – diodedrop (VD) while the low side MOSFET turning on.
R1VCC6.0VRegulatorBOOTC11µFR11012V5V+UGATEVCCC21µFRT9202LGATEFig.2 Dual Power Supply Operation
Power On Reset
The Power-On Reset (POR) monitors the supplyvoltage (normal +5V) at the VCC pin and the inputvoltage at the OCSET pin. The VCC POR level is4.1V with 0.5V hysteresis and the normal level atOCSET pin is 1.5V (see over-current protection). ThePOR function initiates soft-start operation after allsupply voltages exceed their POR thresholds.Soft Start
A built-in soft-start is used to prevent surge currentfrom power supply input during power on. The soft-start voltage is controlled by an internal digitalcounter. It clamps the ramping of reference voltage atthe input of error amplifier and the pulse-width of theoutput driver slowly. The typical soft-start duration is2mS.
Over-Current Protection
The over current protection (OCP) function of theRT9202 is triggered when the voltage across theRDS(ON) of upper side MOSFET that developed bydrain current exceeds over-current tripping level. Anexternal resistor (ROCSET) programs the over-currenttripping level of the PWM converter. As shown onFig.1, the internal 40µA current sink (IOCSET) developsa voltage across ROCSET (VSET) that is referenced toVIN. The DRIVE signal enables the over-currentcomparator (OC). When the voltage across the upperMOSFET (VDS(ON)) exceeds VSET, the over-current
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C21µFVCCBOOTUGATEPHASED10.1µF+5VVCCLGATERT9202Fig.1 Single 5V power Supply OperationDual Power Operation
The RT9202 was designed to regulate a 6.0V at VCCpin automatically when BOOT pin is powered by 12V.In a system with ATX 5V/12V power supply, theRT9202 is ideal for higher current application due tothe higher gate driving capability, VUGATE = 7V andVLGATE = 6.0V. A RC (10Ω/1µF) filter is alsorecommended at BOOT pin to prevent the ringinginduced from fast power on, as shown in Fig.2.
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RT9202comparator trips to set the over-current latch. BothVSET and VDS are referenced to VIN and a smallcapacitor across ROCSET helps VOCSET tracking thevariations of VIN due to MOSFET switching. The over-current function will be tripped at a peak inductorcurrent (IPEAK) determined by:The OC trip point varies with MOSFET’s RDS(ON)temperature variations. The temperature coefficientof IOCSET is 2500ppm that is used to compensateRDS(ON) temperature variations. To avoid over-currenttripping in the normal operating load range,determine the ROCSET resistor value from the equationabove with:1. The maximum RSD(ON) at the highest junctiontemperature2. The minimum IOCSET from the characteristics3. Determine IPEAK for IPEAK > IOUT(MAX) + (∆I)/2where ∆I is the output inductor ripple current.COUNT = 1COUNT = 2InternalSS4V2V0VOVERLOADAPPLIEDCOUNT = 3INDUCTOR CURRENT0AT0T1T2TIMET3Fig. 4ShutdownPulling low the OCSET pin by a small singletransistor can shutdown the RT9202 PWM controlleras shown in typical application circuit.OVER-CURRENT TRIP:VDS > VSETiD ×R DS(ON) > IOCSET × ROCSETVIN = +5VROCSETVSET+iDOCSETIOCSET40µADRIVE+_VCCUGATEVDS+OCPWMGATECONTROLPHASEVPHASE = VIN - VDSVOCSET = VIN - VSETFig.3Under Voltage and Over Voltage ProtectionThe voltage at FB pin is monitored and protectedagainst OC (over current), UV (under voltage), andOV (over voltage). The UV threshold is 0.5V and OV-threshold is 1.0V. Both UV/OV detection have 30µStriggered delay. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Fig.4.Only 3 times of trigger are allowed to latch off. Hiccupis disabled during soft-start interval.www.richtek.com
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DS9202-02 August 2002
RT9202
Applications Information
Inductor Selection
The RT9202 was designed for VIN = 5V, step-downapplication mainly. Fig.5 shows the typical topologyand waveforms of step-down converter.
The ripple current of inductor can be calculated asfollows:
ILRIPPLE = (5V - VOUT)/L × TONBecause operation frequency is fixed at 300kHz,
TON = 3.33 × VOUT/5VThe VOUT ripple is
VOUT RIPPLE = ILRIPPLE × ESRESR is output capacitor equivalent series resistorTable 1 shows the ripple voltage of VOUT: VIN = 5V
iLQLVLVIDCRVOC.C.M.TSTONTOFFVI - VOVL- VOµQIL = IOµIL iQIQiDIDFig.5
Table 1
VOUTInductor
1000µF (ESR=53mΩ)1500µF (ESR=33mΩ)3000µF (ESR=21mΩ)
2µH100mV62mV40mV
3.3V
5µH40mV25mV16mV
2µH110mV68mV43mV
2.5V
5µH44mV28mV18mV
2µH93mV58mV37mV
1.5V
5µH37mV23mV15mV
*Refer to Sanyo low ESR series (CE, DX, PX…)The suggested L and C are as follows:2µH with ≥ 1500µF COUT5µH with ≥ 1000µF COUT
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RT9202Input / Output CapacitorHigh frequency/long life decoupling capacitors shouldbe placed as close to the power pins of the load asphysically possible. Be careful not to add inductanceto the PCB trace, as it could eliminate theperformance from utilizing these low inductancecomponents. Consult with the manufacturer of theload on specific decoupling requirements.The output capacitors are necessary for filteringoutput and stabilizing the close loop (see the PWMloop stability). For powering advanced, high-speedprocessors, it is required to meet with therequirement of fast load transient, high frequencycapacitors with low ESR/ESL capacitors arerecommended.Another concern is high ESR induced ripple maytrigger UV or OV protections.PWM Loop StabilityThe RT9202 is a voltage mode buck controllerdesigned for 5V step-down applications. The gain oferror amplifier is fixed at 35dB for simplified design.The output amplitude of ramp oscillator is 1.6V, theloop gain and loop pole/zero are calculated asfollows:DC loop gain GA = 35dB × ×Error Amp pole PA = 300kHzESR zero ZO = × π × ESR × CThe RT9202 Bode plot as shown Fig.6 is stable inmost of application conditions.VOUT = 3.3VCOUT = 1500µF(33mΩ)L=2µH40VOUT = 1.5VVOUT = 2.5V30VOUT = 3.3VPO = 2.9kHzZO = 3.2kHzReference VoltageBecause RT9202 use a low 35dB gain error amplifier,shown in Fig. 7. The voltage regulation is dependenton VIN & VOUT setting. The FB reference voltage of0.8V were trimmed at VIN = 5V & VOUT = 2.5Vcondition. In a fixed VIN = 5V application, the FBreference voltage vs. VOUT voltage can be calculatedas Fig. 8.I356KFBI21KREP0.8V_RAMP1.75V_EA++PWM+_Fig. 70.820.81FB (V)0.800.790.780.5VIN = 5V11.522.5VOUT (V)33.544.551.61LC filter pole PO = × π ×LC2120.8VOUTFig. 8Feedback DividerThe reference of RT9202 is 0.8V. The output voltagecan be set using a resistor based divider as shown inFig.9. Put the R1 and R2 as close as possible to FBpin and R2 should less than 1 kΩ to avoid noisecoupling. The C1 capacitor is a speed-up capacitorfor reducing output ripple to meet with therequirement of fast transient load. Typically a 1nF ~0.1µF is enough for C1.20Loop Gain101001k10k100k1MFig. 6www.richtek.com
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DS9202-02 August 2002
RT9202
VINLVOUT+COUTR1R2< 1KC1RT9202FBespecially the high-frequency ceramic decouplingcapacitors, close to the power switches. Place theoutput inductor and output capacitors between theMOSFETs and the load. Also locate the PWMcontroller near by MOSFETs.
A multi-layer printed circuit board is recommended.Fig.10 shows the connections of the criticalcomponents in the converter. Note that the capacitorsCIN and COUT each of them represents numerousphysical capacitors. Use a dedicated grounding planeand use vias to ground all critical components to thislayer. Apply another solid layer as a power plane andcut this plane into smaller islands of common voltagelevels. The power plane should support the inputpower and output power nodes. Use copper filledpolygons on the top and bottom circuit layers for thePHASE node, but it is not necessary to oversize thisparticular island. Since the PHASE node is subjectedto very high dV/dt voltages, the stray capacitanceformed between these island and the surroundingcircuitry will tend to couple switching noise. Use theremaining printed circuit layers for small signalrouting. The PCB traces between the PWM controllerand the gate of MOSFET and also the tracesconnecting source of MOSFETs should be sized tocarry 2A peak currents.
Fig. 9
PWM Layout Considerations
MOSFETs switch very fast and efficiently. The speedwith which the current transitions from one device toanother causes voltage spikes across theinterconnecting impedances and parasitic circuitelements. The voltage spikes can degrade efficiencyand radiate noise, that results in ocer-voltage stresson devices. Careful component placement layout andprinted circuit design can minimize the voltage spikesinduced in the converter. Consider, as an example,the turn-off transition of the upper MOSFET prior toturn-off, the upper MOSFET was carrying the full loadcurrent. During turn-off, current stops flowing in theupper MOSFET and is picked up by the low sideMOSFET or Schottky diode. Any inductance in theswitched current path generates a large voltage spikeduring the switching interval. Careful componentselections, layout of the critical components, and useshorter and wider PCB traces help in minimizing themagnitude of voltage spikes.
There are two sets of critical components in a DC-DCconverter using the RT9202. The switching powercomponents are most critical because they switchlarge amounts of energy, and as such, they tend togenerate equally large amounts of noise. The criticalsmall signal components are those connected tosensitive nodes or those supplying critical bypasscurrent.
The power components and the PWM controllershould be placed firstly. Place the input capacitors,
IQ1ILVOUT5V+Q1IQ2Q2GND++LOADLGATEUGATEVCCGNDFBRT9202Fig. 10
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RT9202Package InformationH A M JBFCI DSymbolABCDFHIJMDimensions In MillimetersMin4.8013.8101.3460.3301.1940.1780.1025.7910.406Max5.0043.9881.7530.5081.3460.2540.2546.1981.270Dimensions In InchesMin0.1890.1500.0530.0130.0470.0070.0040.2280.016Max0.1970.1570.0690.0200.0530.0100.0100.2440.050www.richtek.com
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DS9202-02 August 2002
RT9202
DS9202-02 August 2002www.richtek.com
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RT9202
RICHTEK TECHNOLOGY CORP.
Headquarter
5F, No. 20, Taiyuen Street, Chupei CityHsinchu, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
RICHTEK TECHNOLOGY CORP.
Taipei Office (Marketing)
8F-1, No. 137, Lane 235, Paochiao Road, Hsintien CityTaipei County, Taiwan, R.O.C.
Tel: (8862)89191466 Fax: (8862)89191465Email: marketing@richtek.com
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DS9202-02 August 2002
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