LD7765 LEADTREND | Alldatasheet
Document overview
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Technical content
Features
High-Voltage (500V) Startup Circuit on HV pin Brown-in/out Function on HV pin X-Cap Discharge function on HV pin Frequency Trembling for EMI improve Green Mode Control for Power Saving Current Mode control with Slope Compensation OVP (Over Voltage Protection) on Vcc OLP (Over Load Protection) OTP (Over temperature protection) Soft Start Soft Driving +500mA/-800mA Driving Capability
Applications
Switching AC/DC Adaptor and Battery Charger Open Frame Switching Power Supply LCD Monitor/TV Power Typical Application EMI Filter ~AC Input OTP GND COMP CS OUT VCCHV DC Output LD7765
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Pin Configuration YY: Year code (D:2004, E2005…) WW: Week code PP: Production code 2 3 4 7 6 5 TOP MARK YYWWPP YYWWPP OTP COMP CS GND HV NC VCC OUT 2 3 4 6 5 TOP MARK YYWWPP YYWWPP OTP COMP CS GND HV VCC OUT SOP-8 (TOP VIEW) SOP-7 (TOP VIEW)
Ordering Information
Freq. Package Top Mark Shipping LD7765 GS 65KHz SOP-8 LD7765GS 2500 /tape & reel LD7765 GR 65KHz SOP-7 LD7765GR 2500 /tape & reel The LD7765 is ROHS compliant/ green packaged. Protection Mode VCC OVP OLP External OTP Internal OTP Auto recovery Auto recovery Latch Auto recovery
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Pin Descriptions PIN NAME FUNCTION
1 OTP
Pulling this pin be low 0.5V wi ll shut down the controller to enter latch mode . Connecting a NTC between this pin and ground will achieve OTP protection function.
2 COMP
Voltage feedback pin. Connect a photo-coupler with it to close the control loop and achieve the regulation. 3 CS Current sense pin. Connect it to sense the MOSFET current
4 GND Ground
5 OUT Gate drive output to drive the external MOSFET
6 VCC Supply voltage pin
7 NC Unconnected Pin
Connect this pin to Line/Neutral of AC main voltage through resistors to provide the startup current for the controller. When Vcc v oltage increases to trip the point of UVLO(on), this HV loop will be turned off to reduce the power loss on the startup circuit. HV pin Internal Resistor divider will detect the AC peak voltage, and provide Brown in/out function. HV pin internal circuit will discharge X-cap’s energy through HV current source when AC line is disconnected.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Block Diagram Delay Time Green Mode OSC Control Internal Bias&Ref Σ UVLO Comparator HV CC 17V/8.5V Slope Compensation 0.650 OCP Comparator 26V OVP Soft -Drive Q Q SET CLR S RPWM Comparator 4.6V OLP Comparator Q Q SET CLR S RPG PDR Q Q SET CLR S R Protection PG OVP 2R R2Vf PG Vref OK Vcc OK OLP OLP Protection GND CS COMP Gate HV VCC 6 5.3V LEB 3 6.5V PDR 0.475/0.525V External OTP Vbias OLP Ext. OTP BNO X Cap. Brown-out Detection X-Cap. Discharge Decection VHV / K BNO X Cap.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Absolute Maximum Ratings VCC -0.3V~30V HV -0.3V~500V COMP, OTP, CS -0.3V ~6V OUT -0.3V ~Vcc+0.3V Power Dissipation, PD@85C SOP-8/SOP-7 250mW Package Thermal Resistance SOP-8/SOP-7,ΘJA 160 °C/W Junction Temperature 150°C Lead Temperature (Soldering, 10sec) 260°C Storage Temperature Range -55°C to 125°C ESD Voltage Protection, Human Body Model (except HV Pin) 2.5KV ESD Voltage Protection, Machine Model (except HV Pin) 250V ESD Voltage Protection, Human Body Model (HV Pin) 1KV ESD Voltage Protection, Machine Model (HV pin) 200V Gate Output Current +500/-800mA Recommended Operating Conditions Supply Voltage Vcc 10V to 24V VCC Capacitor 10 to 47µF HV Pin Resistor 5~10kΩ COMP Capacitor Value 1~100nF Operating Ambient Temperature -40°C to 85°C Operating Junction Temperature Range -40°C to 125°C Note: 1. COMP pin connecting a capacitor is essential to filter out the undesired switching noise for stable operation. 2. The small signal components as closed to IC pin as possible. Caution: Stress exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above t he Recommended Operating Conditions is not implied. Extended exposure to stress above Recommended Operating Conditions may affect device reliability.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V) PARAMETER CONDITIONS MIN TYP MAX UNITS High-Voltage Supply (HV Pin) High-Voltage Current Source Vcc< UVLO(on), HV=500V 2 4.5 mA HV Pin Total Input Current HV=500Vdc,Vcc>UVLO(on), 45 A HV Pin Brown –In Level(HVBI) HV pin = rectifier wave increase 89 95.0 101 Vac(peak) HV Pin Brown-out Level(HVBO) HV pin = rectifier wave decrease 71.9 76.5 81.1 Vac(peak) Brown-in De-bounce Time 160 210 260 s Brown-out Detection Debounce Time 45 55 65 ms HV Discharge capability HV=500V,Vcc < UVLO(on) - 1 2 4.5 mA Supply Voltage (Vcc Pin) Startup Current Vcc=15V ,HV=500V 160 300 A Operating Current (with 1nF load on OUT pin) VCOMP=3V 1.5 2.0 2.5 mA VCOMP=0V 0.30 0.62 0.65 mA OLP,OVP Tripped 0.3 0.4 0.5 mA UVLO (off) 8.0 8.5 9.0 V UVLO (on) 16.0 17.0 18.0 V PDR 6 6.5 7.0 V Vcc OVP Level 25.00 26.25 27.50 V Voltage Feedback (Comp Pin) Short Circuit Current VCOMP=0V 105 125 145 A Open Loop Voltage COMP pin open 5.1 5.3 5.5 V OLP Tripped Level 4.4 4.6 4.8 V Fix Frequency Mode Threshold(*) - 2.8 - V Green Mode Threshold(*) - 2.3 - V Zero Duty Threshold VCOMP Zero Duty,VFB_B 1.69 1.80 1.91 V Zero Duty-recover 1.80 1.90 2.00 V Current Sensing (CS Pin) Maximum Input Voltage, VCS_OFF 0.620 0.650 0.680 V Maximum Input Voltage, VCS_MIN For High Line 0.445 0.475 0.515 V Leading Edge Blanking Time -20C ~125C 150 215 280 ns Delay to Output 50 100 150 ns
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 (TA = +25C unless otherwise stated, VCC=15.0V) PARAMETER CONDITIONS MIN TYP MAX UNITS Oscillator for Switching Frequency Frequency 62 65 68 KHz Trembling Frequency ±4 ±5 ±6 % Green Mode Frequency 23.6 25.6 27.6 KHz Fsw Temp. Stability(*) -40C ~105C - 5 - % Fsw Voltage Stability(*) Vcc=UVLO(off)~(Vcc OVP-1V) - 1 - % Maximum Duty 70 75 80 % Gate Drive Output (OUT Pin) Output Low Level VCC=15V, Io=20mA 0 - 1 V Output High Level VCC=15V, Io=20mA 9 - Vcc V Rising Time(*) Load Capacitance=1000pF , 4V~90% Output High Level - 100 - ns Falling Time(*) Load Capacitance=1000pF - 48 - ns OUT Pin Clamping Voltage VCC=21V,1nF on OUT pin 14 15 16 V OLP (Over Load Protection) OLP Delay Time Auto restart, FSW=65KHz 57 63 69 ms OLP De-Latch Counter Auto-Restart Mode - 2 - Soft Start Soft Start Duration 3 4 5 ms External Over Temperature Protection(OTP Pin) OTP pin Source Current 46 50 54 A Turn-on Tripped Level (VOTP_on) 0.500 0.525 0.550 V Turn-off Tripped Level (VOTP_off) VOTP_ON-0.05 V OTP Detect De-bounce cycle - 16 - PWM cycle De-latch Level UVLO(off)/AC-off Internal OTP OTP Tripped Level(TOTP) () - 140 - C OTP Hysteresis() - TOTP-30 - C OTP Protection Auto Recovery by Vcc UVLO Notes: Guaranteed by design.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Typical Performance Characteristics
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Typical Performance Characteristics
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012
Application Information
As long as the green power requirement becomes a trend and the power saving is getting more and more important for the switching power supplies and switching adaptors, the traditional PWM controllers are not able to support such new requirements. Furthermore, the cost and size limitation force the PWM controllers need to be powerful to integ rate more functions to reduce the external part counts. The LD7765 is ideal for these applications to provide an easy and cost effective solution; its detailed features are described as below. Internal High -Voltage Startup Circuit and Under Voltage Lockout (UVLO) The traditional circuit provides the startup current through a startup resistor to power up the PWM controller. However, it consumes much significant power to meet the current power saving requirement. In most cases, startup resistors carry larger resistance and spend more time to start up. As shown in Fig 9 , LD7765 is implemented with a high-voltage startup circuit with it to minimize power loss on startup circuit. During the startup transient, a high-voltage current source sinks current from AC Line or Neutral to provide the startup c urrent and charge the Vcc capacitor C1 the same time. See in Fig 10 . Once VCC voltage rises up to reach the UVLO(on) threshold, HV pin will stop charging the VCC capacitor and BNO will detect the AC line status. In the meantime, VCC voltage begins to fall and consumes less current for operation from 0.6mA to 300A as it’s falling to UVLO(off) As VCC trips UVLO(off), HV pin will recharge VCC capacitor till VCC voltage rises back to UVLO(on) again. Since then, HV pin would no longer cha rge the capacitor and instead, send a gate drive signal to draw supply current for VCC from the auxiliary winding of the transformer. That minimizes the power loss on the start-up circuit successfully. By using such configuration, the turn-on delay time will be almost same no matter under low -line or high -line conditions. An UVLO comparator is embedded to detect the voltage across Vcc pin to ensure the supply voltage enough to power on the LD7765 and in addition to drive the power MOSFET. As shown in Fig 10, a hysteresis is provided to prevent the shutdown from the voltage dip during startup. The turn -on and turn -off threshold level are set at 17V and 8.5 V, respectively. CS VCC GND AC input Cbulk HV current source Rs PWM IC Fig 9.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Vcc UVLO(on) UVLO(off) t t HV Current 3mA Startup Current (<300uA) Vcc current ~ 0mA (off) Operating Current (Supply from Auxiliary Winding) BNO detecting Operation &Switching Operation Current ~0.6mA Fig 10. Brown In/ Out Protection The LD7765 features Brown -in / Brown-out protection on HV pin. As the built -in comparator detects line voltage, it will turn off the controller to prevent from any damage. In case V HV<VHBO, the gate output will be disabled even when the VCC already reach UVLO(ON). It therefore forces VCC hiccup between ULVO(ON) and UVLO(OFF). Unless the line voltage is large enough and over HVBI VAC, the gate output will not start switching even as the next ULVO(ON) is tripped. A hysteresis is designed to prevent from false-triggering and damage to the external components during turn-on and turn -off transient. See Fig 11 for the operation. BNO/on t Vcc t OUT SwitchingNon-Switching t VHV(peak) t Line Voltage BNO/off Non- Switching AC OK area UVLO(on) UVLO(off) Fig 11. Current Sensing, Leading -Edge Blanking and the Negative Spike on CS Pin The typical current mode PWM controller feedbacks both current signal and voltage signal to close the control loop and achieve regulation. The LD7765 detects the primary MOSFET current across the CS pin, which is not only for the peak current mode control but also for the pulse-by-pulse current limit. The maximum voltage threshold of the current sensing pin is set at 0. 65V (typ.). Thus the MOSFET peak current can be calculated as: S )MAX(PEAK R V65.0I A 250ns (typical) leading-edge blanking (LEB) time is provided in the input of CS pin to prevent false -triggering from the current spike. In the low powe r applications, the total pulse width of the turn -on spike is determined by the output power, circuit design and PCB lay out. It is strongly recommended to add a small R-C filter (as shown
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 in Fig 12) for large power applications to avoid the VCS < -0.3V from being damaged by the negative turn-on spike. CS VCC GND LD7765 R-C filter is required if the negative spike exceeds -0.3V or the total spike width is over 150nS LEB period. OUT Rs Leading Edge Blanking Fig 12. OCP Compensation Design Tip The typical current mode PWM controller feedbacks both current signal and voltage signal to close the control loop and achieve regulation. The LD7765 detects the primary MOSFET current across the CS pin, which is not only for the peak current mode control but also for the pulse-by-pulse current limit. In general, the power converter provides various current in reflect to the input voltage during signal propagation delay time. To compensate it , LD7765 varies the current limit in corresponding to Vcs _off with the duty cycles. As shown Fig 13, Vcs_off (corresponding to current limit) is in direct proportion to duty ratio in certain segment and is fixed at high or low as duty ratio is over or below threshold values respectively. As a result, the current limit will be reduced at high -line inputs. This compensation control mechanism is developed and protected with Leadtrend’s patents. (Patent pending), VCS VCS_off VCS_min Duty (%)20% 55% Fig 13. Voltage Feedback Loop The voltage feedback signal is provided from the TL431 on the secondary side through the photo -coupler to the COMP pin of LD7765 The input stage of LD 7765, like UC384X, is with 2 diodes voltage offset to feed the voltage divider with 1/4 ratio, that is, )V2V(3 1V FCOMP)PWM(cs COMPARATOR A pull-high resistor is embedded internally to optimize the external circuit. Internal Slope Compensation A fundamental issue of current mode control is the stability problem when its duty -cycle is operated for more than 50%. To stabilize the control loo p, the slope compensation is required in the traditional UC384X design by injecting the ramp signal from the RT/CT pin through a coupling capacitor. In LD7 765, the internal slope compensation circuit has been implemented for a compact external circuit design. Oscillator and Switching Frequency The switching frequency of LD7 765 is fixed at 65KHz to provide optimized operations in considering the EMI performance, thermal treatment, component sizes and transformer design. The frequency swapping is internally pre-set for 4kHz when incorporating with 65KHz switching frequency.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Green-Mode Operation By using the green-mode control, the switching frequency can be reduced under the light load condition. This feature helps to improve the efficiency in light load conditions. The green -mode control is Leadtrend Technology’s own IP. Maximum Duty-Cycle The maximum duty -cycle of LD7 765 is limited to 75% to avoid the transformer saturation. On/Off Control The gate driver of LD7 765 can be disabled immediately by pulling COMP pin voltage level lower than Zero Duty Trip Level. The disa ble-mode can be released when Comp pin voltage level is pulled high above Zero Duty Trip Level. Over Load Protection (OLP)- Auto Recovery To protect the circuit from being damaged at over load condition, short or open loop condition, the LD7765 is implemented with smart OLP function. LD7765 features auto recovery function, see Fig 14 for the waveform. In the example of the fault condition, the feedback system will force the voltage loop enter toward saturation and then pull the voltage high across COMP pin (VCOMP). When the VCOMP ramps up to the OLP tripped level (4.6V) for more than the OLP delay time , the protection will be activated to turn off the gate output and to stop the switching of power circuit. The OLP delay time is set by internal high frequency counter. It is to prevent the false triggering during the power-on and turn-off transient. A divide-2 counter is implemented to reduce the a verage power under OLP behavior. Whenever OLP is activated, the output is latched off and the divi de-2 counter starts to count the number of UVLO(off). The latch will not be released and the output will not be resumed until the 3rd UVLO(off) level is tripped. With the protection mechanism, the average input power will be less than ever, so that the component temperature and stress can be controlled within the safe operating area. VCC UVLO(on) UVLO(off) t t COMP OLP VOLP t OUT OLP Delay Time Switching SwitchingNon-Switching OLP trip Level 2nd UVLO(off) OLP Counter Reset BNO Detecting Fig 14. OVP (Over Voltage Protection) on Vcc - Auto Recovery The maximum Vcc ratings of the LD7765 are mostly for 30V. To protect the controller in over -voltage condition, LD7765 is implemented with OVP function on VCC. Once the VCC voltage ramps over the OVP threshold, it will shut off the output gate drive circuit right away and disable the power MOSFET until the 2nd UVLO(ON) is tripped. The Vcc OVP functio n is auto-recoverable. If the OVP condition, usually caused by open-loop of feedback, is not released, the Vcc will trip the OVP level again and re-shutdown the output to resume. That makes the Vcc work in hiccup mode. Fig 15 shows its operation. After the OVP condition is removed, the Vcc will resume its operation level and the output in the normal operation.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 VCC UVLO(on) UVLO(off) t OVP Tripped t OUT Switching Switching Non-Switching OVP Level OUT Clamping Fig 15. On-Chip OTP - Auto Recovery An internal OTP circuit is embedded in the LD7765 to provide the worst-case protection for this controller. When the chip temperature ramps higher than the trip OTP level, the output will be disabled until the chip is cooled down below the hysteresis window. X-Cap Discharge Function The EMI filter has a paralleled discharging resistor across X-capacitor. To meet Safety requirement, t his component is required to be discharged in less than 1sec, that is, sec1RC eargDischCapXeargDisch The power loss of this resistor is in direct proportion to square of input voltage. For example, if the input voltage is 264Vac and the discharging resistance ~ 2M, 35mW power loss can be calculated by follow equation. eargDisch (RMS) AC Loss R V P To eliminate the significant power loss from this discharging resistor, LD7765 applies the innovative patent technology to discharge X -cap’s energy through HV current source when AC line is disconnected. Fig 16 shows the operation. Applying this technology , the system can easily pass the safety test without discharging resistor and reduced power loss After the plug is pulled out, the AC voltage on X-cap would still remain. The LD7765 senses the HV pin to detect the state of the AC voltage on X-cap. LD7765 sets a threshold voltage to judge whether the AC voltage on X -cap is higher than this threshold with no rising cross in a de-bouncing time. If so, LD7765’s HV device will sink constant current source to GND. This discharging function is applicable at all load conditions in a de-bouncing time of X-cap function around 55ms. Gate CS VCC GND AC input Cbulk PWM IC Rs AC detected CKT Fig 16. External OTP - Latched Mode Protection The OTP circuit is implemented to sense whether there is any hot-spot of power circuit like power MOSFET or output rectifier. Once an over -temperature condition is detected, the OTP is enabled to shut down the controller to protect the controller. Typically, a NTC is recommended to connect with OTP pin. The NTC resistance will decrease as the device or ambient in high temperature. The relationship is as below. NTCOTP RAμ50V When VOTP<VOTP-off (typ . 0.5V), it will trigger the protection to shut down the gate output and latch off the power supply. The controller will remain latched unless
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 the Vcc drops below PDR (power down reset) and Vcc stay on UVLO condition . Two conditions are required to restart the IC successfully, cool down the circuit so that the NTC resistance will increase and raise V OTP above 0.525V. Then re-plug on AC power. The detailed operation is show in Fig 17. UVLO(on) UVLO(off) t AC input Voltage OTP t OUT Switching Switching Non-Switching t VCC t 0.525V 0.475V VOTP OTP Release PDR AC Off AC On (Recycle) Latch Released Low OTP pin current Fig 17. Pull-Low R esistor on the Gate Pin of MOSFET The LD7765 consists of an anti -floating resistor on the OUT pin to protect the output from abnormally operation or false triggering by MOSFET. Even so, we still recommend to add an external one on the MOSFET gate terminal to provide more protection in case of disconnection of gate resistor RG during power-on. In such single -fault condition, as show n in Fig 18 , the resistor R8 can provide a discharge path to avoid the MOSFET from being false-triggered by the current through the gate -to-drain capacitor C GD. Therefore, the MOSFET should be pulled low and placed in the off-state no matter that the gate resistor is disconnected or opened. CS GND LD7765 A resistor is recommended to be placed here. OUT Rg The built-in internal pull-low resistor can prevent from floating. Fig 18. MOSFET Characteristic The MOSFET is divided into three operat ion regions, ohmic region, saturation region, and the cut -off region , shown as Fig 19. For switching power supply applications, it shall operate in ohmic and cut -off region. Never reach the region of saturation; it would cause damage for acting beyond the maximum safe ty operating area. It’s necessary to check the characteristic of MOSFET. Fig 20 shows a totem pole architecture for the circuit of OUT. The output high level of OUT is at around VCC-1.5V. The maximum voltage for VS is equal to V CS_OFF. So we obtain the minimum VGS high level (VGSH(MIN)) as below. of f_Vcs5.1)of f(UVLOVGS )MIN(H The maximum peak current of MOSFET can be calculated as: S )MAX(PEAK R of f_VcsI Refer to on-region characteristics of the MOSFET (like Fig 19), check the saturation current of VGSH(MIN) to make
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 sure the saturation current is higher th an I PEAK(MAX). In order not to decrease the voltage across VG, it ’s recommended not to connect a forward diode between the gate of the MOSFET and OUT pin , for example like Fig 21. In addition, pulling VCC level high can keep VGSH in high level, for example: 1. Refer to Fig 20, increase NX to pull VCC level high. 2. Refer to Fig 22 , increase VCC capacitance to improve VCC ’s performance to drop at startup transient, shows as Fig 22. VDS ID Ohmic Region Saturation Region VGS1 VGS2 VGS3 VGS4 VGS5 VGS5 > VGS4 > VGS3 > VGS2 > VGS1 Cut-off region Fig 19. CS GND LD7765 OUT VGS VS VCC VG VD VDS RS NX CVCC Fig 20. CS GND VG RS LD7765 OUT Fig 21. VCC t Large Capacitance of VCC Cap Small Capacitance of VCC Cap UVLO(on) Fig 22.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012
Package Information
Dimensions in Millimeters Dimensions in Inch MIN MAX MIN MAX A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 θ 0° 8° 0° 8°
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012 Dimensions in Millimeters Dimensions in Inch MIN MAX MIN MAX A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 θ 0° 8° 0° 8° Important Notice Leadtrend Technology Corp. reserves the right to make changes or corrections to its products at any time without notice. Cust omers should verify the datasheets are current and complete before placing order.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7765-DS-00 October 2012
Revision History
Rev. Date Change Notice 00 10/29/2012 Original Specification.