LD7537R英文说明书
LD7537R 7 01 2010 1 Leadtrend Technology Corporation tw LD7537R DS 00a July 2010 Green Mode PWM Controller with Frequency Swapping and Integrated Protections Rev 00a General Description The LD7537R is built in with several functions protection and EMI improved solution in a tiny package It takes less components counts or circuit space especially ideal for those total solutions of low cost The implemented functions include low startup current green mode power saving operation leading edge blanking of the current sensing and internal slope compensation It also features more protections like OLP Over Load Protection and OVP Over Voltage Protection to prevent circuit damage occurred under abnormal conditions Furthermore the Frequency Swapping function is to reduce the noise level and thus helps the power circuit designers to easily deal with the EMI filter design by spending minimum amount of component cost and developing time Features High Voltage CMOS Process with Excellent ESD protection Very Low Startup Current 20 A Current Mode Control Green Mode Control UVLO Under Voltage Lockout LEB Leading Edge Blanking on CS Pin Internal Frequency Swapping Internal Slope Compensation OVP Over Voltage Protection on Vcc Pin Brownout Protection OLP Over Load Protection 300mA Driving Capability Applications Switching AC DC Adaptor and Battery Charger Open Frame Switching Power Supply Typical Application EMI Filter BNOOUT CS VCC GND COMP LD7537R photocoupler AC input DC Output LD7537R 2 Leadtrend Technology Corporation tw LD7537R DS 00a July 2010 Pin Configuration DIP 8 TOP VIEW SOT 26 TOP VIEW YY Y Year code D 2004 E 2005 WW W Week code PP Production code P37R LD7537R 123 456 GNDCOMPOTP OUTVCCCS YWP 1 8 2 3 4 7 6 5 TOP MARK YYWWPP OUT VCC NC CS GND COMP NC OTP 37R pp Ordering Information Part number Package Top Mark Shipping LD7537R GL SOT 26 Green Package YWP 37R 3000 tape see Fig 18 for the waveform In case of fault condition the feedback system will force the voltage loop toward the saturation and then pull the voltage high on COMP pin VCOMP When the VCOMP ramps up to the OLP threshold of 4 5V and continues over OLP delay time the protection will be activated and then turn off the gate output to stop the switching of power circuit With the protection mechanism the average input power will be minimized to remain the component temperature and stress within the safe operating area VCC UVLO on UVLO off t t COMP OLP 4 5V t OUT OLP delay time SwitchingSwitchingNon Switching OLP trip Level UVLO off OLP Reset Fig 18 OVP Over Voltage Protection on Vcc Auto Recovery The maximum VGS ratings of the power MOSFETs are mostly for 30V To prevent the VGS enter fault condition LD7537R series are implemented with OVP function on Vcc Whenever the Vcc voltage is higher than the OVP threshold the output gate drive circuit will be shutdown simultaneously and the switching of the power MOSFET is disabled until the next UVLO on The Vcc OVP functions of LD7537R are auto recoverable If the OVP condition usually caused by open loop of feedback is not released the Vcc will tripped the OVP level again and re shutdown the output The Vcc works in hiccup mode Figure 19 shows its operation Otherwise when the OVP condition is removed the Vcc level will be resumed and the output will automatically return to the normal operation LD7537R 12 Leadtrend Technology Corporation tw LD7537R DS 00a July 2010 VCC UVLO on UVLO off t OVP Tripped t OUT Switching SwitchingNon Switching OVP Level Fig 19 Brownout Protection The LD7537R programmable to set the brownout protection point though BNO pin The voltage across the BNO pin is proportional to the bulk capacitor voltage referred as the line voltage A brownout comparator is implemented to detect the abnormal line condition As soon as the condition is detected it will shut down the controller to prevent the damage Figure 20 shows the operation When VBNO falls below 0 80V the gate output will be kept off even Vcc has already achieved UVLO ON It therefore makes Vcc hiccup between UVLO ON and UVLO OFF Unless the line voltage is large enough to pull VBNO larger than 1 05V the gate output will not start switching even when the next UVLO ON is tripped A hysteresis is implemented to prevent the false trigger during turn on and turn off Figure 20 shows the circuit Fig 20 Oscillator and Switching Frequency The LD537R is implemented with Frequency Swapping function which helps the power supply designers to both optimize EMI performance and lower system cost The switching frequency substantially centers at 65KHz and swap between a range of 4KHz 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 property Fault Protection There are several critical protections integrated in the LD7537R to prevent from damage to the power supply LD7537R 13
