CX7501 CXW | Alldatasheet
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Technical content
Quasi-Resonant PSR CC/CV PWM Power Switch
FEATURES
LowCostSolutionBuilt-in800VpowerBJT Quasi-Resonant Primary Side Regulation (QR-PSR)ControlwithHighEfficiency Multi-ModePSRControl FastDynamicResponse Built-inDynamicBaseDrive AudioNoiseFreeOperation ±4%CCandCVRegulation LowStandbyPower<70mW Programmable Cable Drop Compensation (CDC)inCVMode Built-inACLine&LoadCCCompensation BuildinProtections: ShortLoadProtection(SLP) Cycle-by-CycleCurrentLimiting LeadingEdgeBlanking(LEB) PinFloatingProtection VDDOVP&UVP&Clamp Overtemperatureprotection(OTP) Available with V e r s i o n s i n S O P Package
APPLICATIONS
BatteryChargersforCellularPhones AC/DCPowerAdapterandLEDLightings GENERAL DESCRIPTION C X is a high performance Quasi Resonant (QR) Primary Side Regulation (PSR) PWM power switch with high precision CV/CC control ideal for chargerapplications. In CV mode, CX7501 a d o p t s M u l t i M o d e Q R Control which uses the hybrid of AM (Amplitude Modulation) mode and (Frequency Modulation) FM mode to improve system efficiency and reliability. In CC mode, the IC uses PFM control with line and load CC compensation. The IC can achieve fast dynamic response. The built-in Cable Drop Compensation (CDC) function can provide excellentCVperformance. C X i n t e g r a t e s f u n c t i o n s a n d p r o t e c t i o n s o f Under Voltage Lockout (UVLO), VDD overVoltage Protection (VDD OVP), Cycle-by-cycle Current Limiting (OCP), Short Load Protection (SLP), On- ChipThermalShutdown,VDDClamping,etc. TYPICALAPPLICATION CIRCUIT CX7501 CX7501 CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
1 FB I
Systemfeedbackpinwhichregulatesboththeoutput voltageinCV modeandoutputcurrentinCCmodebasedontheflybackvoltageof theauxiliar y windin g 2 CS I CurrentSense InputPin. 3 VDD P PowerSupplyPinoftheChip.
4 E O ThePowerBJT Emitter
5,6 HV O ThePowerBJTCollector
7 GND P TheGroundoftheIC
Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
AbsoluteMaximumRatings(Note1) Parameter Value Unit HVPINMaximumVoltage 800 V HVPINDCCurrent @CX7501 1300 mA VDDDCSupplyVoltage 30 V VDDDCClampCurrent 10 mA CS,BASEvoltagerange -0.3to7 V FBvoltagerange -0.7to7 V RJA(℃/W)(SOP7) 90 oC/W MaximumJunctionTemperature 150 oC OperatingTemperatureRange -40to85 oC StorageTemperatureRange -65to150 oC LeadTemperature(Soldering,10sec.) 260 oC ESDCapability,HBM(HumanBodyModel) 3 kV ESDCapability,MM(MachineModel) 250 V RecommendedOperationConditions(Note2) Parameter Value Unit SupplyVoltage,VDD 7to24 V OperatingAmbient Temperature -40to85 oC MaximumSwitchingFrequency@FullLoading 70 kHz MinimumSwitchingFrequency@FullLoading 35 kHz ELECTRICAL CHARACTERISTICS(TA=25OC,VDD=20V,ifnototherwisenoted) Symbol Parameter TestConditions Min Typ. Max Unit SupplyVoltageSection(VDDPin) IVDD_st Start-upcurrent intoVDDpin 3 20 uA IVDD_Op OperationCurrent 0.8 1.5 mA IVDD_standby StandbyCurrent 0.5 1 mA VDD_ON VDD Under Voltage Lockout Exit 10.5 12 13.5 V VDD_OFF VDD Under Voltage Lockout Enter 5.5 6.5 7 V VDD_OVP VDDOVPThreshold 24 26.5 29 V VDD_Clamp VDDZenerClampVoltage I(VDD)=7mA 26 28 30 V ControlFunctionSection (FBPin) Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
Internal Error Amplifier (EA) ReferenceInput 1.97 2.0 2.03 V VFB_SLP Short Load Protection (SLP) Threshold 0.65 V TFB_Short Short Load Protection (SLP) DebounceTime (Note3) 36 ms VFB_DEM Demagnetization Comparator Threshold 25 mV Toff_min MinimumOFFtime (Note3) 2 us Ton_max MaximumONtime (Note3) 20 us Toff_max MaximumOFFtime 5 ms ICable_max Maximum Cable Drop Compensation(CDC)Current 60 uA TSW /TDEM Ratio between Switching Period and Demagnetization TimeinCCMode CurrentSenseInputSection (CSPin) TLEB CS Input Leading Edge BlankingTime 500 ns Vcs(max) Currentlimitingthreshold 490 500 510 mV TD_OC Over Current Detection and ControlDelay 100 ns On-ChipThermalShutdown T SD ThermalShutdown (Note3) --- 155 -- C T RC ThermalRecovery (Note3) 140 -- C BJTSection(HVPin) VCEO Collector-Emitter voltage 480 V VCBO Collector-Base voltage 800 V Note1. Stresses listed as the above "Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to maximum rating conditions for extended periods may remain possibility to affect device reliability. Note2.The device is not guaranteed to function outside its operating conditions. Note3.GuaranteedbytheDesign. Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
i s a h i g h p e r f o r m a n c e m u l t i m o d e h i g h l y integrated Quasi Resonant Primary Side Regulation (QR-PSR) power switch. The built-in high precision CV/CC control with high level protection features makes it suitable for offline smallpowerconverterapplications. SystemStart-Up Operation Before the IC starts to work, it consumes only startup current (typically 3uA) which allows a large value startup resistor to be used to minimize the power loss and the current flowing through the startup resistor charges the VDD hold-up capacitor from the high voltage DC bus. When VDD reaches UVLO turn-on voltage of 12V (typical), CX7501 begins switching and the IC operation current is increased to be 0.8mA (typical). The hold-up capacitor continues to supply VDD before the auxiliary winding of the transformer takes the controlof VDDvoltage. F i g O n c e C X e n t e r s v e r y l o w f r e q u e n c y F M F r e q u e n c y M o d u l a t i o n m o d e t h e o p e r a t i n g c u r r e n t i s r e d u c e d t o b e u A t y p i c a l l y w h i c h h e l p s t o r e d u c e t h e s t a n d b y p o w e r l o s s Q u a s i R e s o n a n t P S R C V M o d u l a t i o n (QR-CVM) In Primary Side Regulation (PSR) control, the output voltage is sensed on the auxiliary winding during the transfer of transformer energy to the secondary. Fig.2 illustrates the timing waveform of CV sampling signal, demagnetization signal (DEM) and quasi-resonant (QR) trigger signal in CX7501. When the CV sampling process is over, the internal sample/hold (S&H) circuit captures the error signal and amplifies it through the internal Error Amplifier(EA). The output of EA is sent tothe Quasi Resonant PSR CV Modulator (QR-CVM) for CV regulation. A valley is selected to trigger new PWM cycle by the output of the QR-CVM bock, which is determined by the load. The internal reference voltage for EA is trimmed to 2V with high accuracy. Fig.2 During the CV sampling process, an internal variable current source is flowing to FB pin for Cable Drop Compensation (CDC). Thus, there is a step at FB pin in the transformer demagnetization process, as shown in Fig.2. Fig.2 also illustrates the equation for “demagnetization plateau”, where Vo and VF is the output voltage and diode forward voltage; R1 and R2 is the resistor divider connected from the Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
auxiliary winding to FB Pin, Ns and Na are secondary winding and auxiliary winding respectively. When heavy load condition, the Mode Selector (as shown in “Block Diagram”) based on EA output willswitchtoCCModeautomatically. PSR Constant Current Modulation (PSR-CCM) Timing information at the FB pin and current information at the CS pin allow accurate regulation of the secondary average current. The control law dictatesthat as power is increased in CV regulation and approaching CC regulation the primary peak currentisatIpp(max),asshowninFig.3. F i g R e f e r r i n g t o F i g a b o v e t h e p r i m a r y p e a k c u r r e n t t r a n s f o r m e r t u r n s r a t i o s e c o n d a r y d e m a g n e t i z a t i o n t i m e T d e m a n d s w i t c h i n g p e r i o d T s w d e t e r m i n e s t h e s e c o n d a r y a v e r a g e o u t p u t c u r r e n t I o u t I g n o r i n g l e a k a g e i n d u c t a n c e e f f e c t s t h e e q u a t i o n f o r a v e r a g e o u t p u t c u r r e n t i s s h o w n i n F i g W h e n t h e a v e r a g e o u t p u t c u r r e n t I o u t r e a c h e s t h e r e g u l a t i o n r e f e r e n c e i n t h e P r i m a r y SideConstant Current Modulator(PSR-CCM)block, the IC operates in pulse frequency modulation (PFM) mode to control the output current at any output voltage at or below the voltage regulation target as long as the auxiliary winding can keep VDDabovetheUVLO turn-offthreshold. In CX7501 the ratio between Tdem and Tsw in CC mode is 4/7. Therefore, the average output current canbeexpressedas: Rcs 500mVN7 2mAICC_OUT Intheequationabove, N----The turn ratio of primary side winding to secondarysidewinding. Rcs--- the sensing resistor connected between the powerBJTemittertoGND. MultiModeControlin CVMode To meet the tight requirement of averaged system efficiency and no load power consumption, a hybrid of frequency modulation (FM) and amplitude modulation (AM) is adopted in CX7501 which is shownintheFig4. Around the full load, the system operates in FM mode. When normal to light load conditions, the IC operates in FM+AM mode to achieve excellent regulation and high efficiency. When the system is near zero loading, the IC operates in FM again for standby power reduction. In this way, the no-load consumptioncanbelessthan70mW. Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
Fig.4 Programmable Cable Drop Compensation(CDC) inCVMode In smart phone charger application, the battery is always connected to the adapter with a cable wire which can cause several percentages of voltage drop on the actual battery voltage. In CX7501 an offset voltage is generated at FB pin by an internal current source (modulated byCDC block, asshown in Fig.5) flowing into the resistor divider. The current is proportional to the switching period, thus, it isinversely proportional to the output power Pout. Therefore, the drop due the cable loss can be compensated. As the load decreases from full loading to zero loading, the offset voltage at FB pin will increase. By adjusting the resistance of R1 and R2 (as shown in Fig.), the cable loss compensation can be programmed. The percentage of maximum compensationisgivenby %100V R1//R2Icable_max Vout V(cable) FB_REF For example, R1=3K Ω , R2=18K Ω , The percentageofmaximumcompensationisgivenby: %7.7%1002V 3K//18K60uA Vout F i g O p t i m i z e d D y n a m i c R e s p o n s e In CX7501, the dynamic response performance is optimizedtomeet USBchargerequirements. O n C h i p T h e r m a l S h u t d o w n O T P When the IC temperature is over 155 oC, the IC shutsdown. Onlywhen the ICtemperaturedrops to 140oC,ICwillrestart. A u d i o N o i s e F r e e O p e r a t i o n As mentioned above, the multi-mode CV control with a hybrid of FM and AM provides frequency modulation. An internal current source flowing to CS pin realizes CS peak voltage modulation. In CX7501 , the optimized combination of frequency modulation and CS peak voltage modulation algorithm can provide audio noise free operation fromfullloadingtozeroloading. D y n a m i c B J T B a s e D r i v e CX7501 drives a power BJT with dynamic base drive control to optimize efficiency. The BJT base Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
drive current ranges from 12mA to 35mA (typical), and is dynamically controlled according to the power supply load change. The higher the output power, the higher the based current. Specifically, the base current is related to CS peak voltage, as showninFig.6 Fig.6 ShortLoadProtection (SLP) In CX7501,the output is sampled on FB pin and then compared with a threshold of UVP (0.65V typically) after an internal blanking time (10ms typical). In CX7501 , when sensed FB voltage is below 0.6V, the IC will enter into Short Load Protection (SLP) mode, in which the IC will enter into auto recoveryprotectionmode. VDDOverVoltage Protection (OVP)and ZenerClamp When VDD voltage is higher than 26.5V (typical), the IC will stop switching. This will cause VDD fall down tobe lower than VDD_OFF (typical6.5V) and then the system will restart up again. An internal 28V (typical) zener clamp is integrated to prevent theICfromdamage. Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD
Symbol DimensionsIn Millimeters DimensionsInInches Min Max Min A 1.350 1.750 A 1.350 A1 0.100 0.250 A1 0.100 A2 1.350 1.550 A2 1.350 b 0.330 0.510 b 0.330 c 0.170 0.250 c 0.170 D 4.700 5.100 D 4.700 e 1.270（BSC） 0.050（BSC） e 1.270（BSC） E1 5.800 6.200 E1 5.800 E 3.800 4.000 L 0.400 1.270 L 0.400 θ 0º 8º θ 0º Quasi-Resonant PSR CC/CV PWM Power Switch CX7501 WWW.CXWIC.COM SHENZHEN CHENGXINGWEI TECHNOLOGY CO.LTD