LD7537

LD7537 LEADTREND | Alldatasheet

Document overview

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Technical content

Features

z High-Voltage CMOS Process with Excellent ESD protection z Very Low Startup Current (<20μA) z Current Mode Control z Green Mode Control z UVLO (Under Voltage Lockout) z LEB (Leading-Edge Blanking) on CS Pin z Internal Frequency Swapping z Internal Slope Compensation z OVP (Over Voltage Protection) on Vcc Pin z Brownout Protection z OLP (Over Load Protection) z 300mA Driving Capability

Applications

z Switching AC/DC Adaptor and Battery Charger z Open Frame Switching Power Supply Typical Application EMI Filter BNO OUT CS VCC GND COMP LD7537 photocoupler AC input DC Output Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Pin Configuration DIP-8 (T OP VIEW) SOT-26 (TOP VIEW) YY, Y : Year code (D: 2004, E: 2005…..) WW, W : Week code PP : Production code P37 : LD7537 123 456 GND COMP BNO OUT VCC CS YWP 2 3 4 7 6 5 TOP MARK YYWWPP OUT VCC NC CS GND COMP NC BNO pp

Ordering Information

Part number Package Top Mark Shipping LD7537GL SOT-26 Green Package YWP/37 3000 /tape & reel LD7537GN DIP-8 Green Package LD7537GN 3600 /tube /Carton The LD7537GL is ROHS compliant. Protection Mode Switching Freq. VCC OVP OLP BNO Pin 65kHz Latch Auto recove ry/ 65ms Auto recovery Pin Descriptions SOT-26 DIP-8 NAME FUNCTION 1 8 GND Ground 2 7 COMP Voltage feedback pin (same as t he COMP pin in UC384X). Connect a photo-coupler to close the control loop and achieve the regulation. 3 5 BNO Brownout Protection Pin. Connect a resistor divider between this pin and bulk capacitor voltage to set t he brownout level. If the voltage is less than threshold voltage, the PWM output will be disabled. 4 4 CS Current sense pin, connect it to sense the MOSFET current 5 2 VCC Supply voltage pin 6 1 OUT Gate drive output to drive the external MOSFET Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Block Diagram Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Absolute Maximum Ratings Supply Voltage VCC -0.3V ~29V COMP, BNO, CS -0.3V ~6V OUT -0.3V ~Vcc+0.3V Maximum Junction Temperature 150 °C Operating Ambient Temperature -40 °C to 85°C Operating Junction Temperature -40 °C to 125°C Storage Temperature Range -65 °C to 150°C Package Thermal Resistance (SOT-26, θJA) 250 °C/W Package Thermal Resistance (DIP-8, θJA) 100 °C/W Power Dissipation (SOT-26) 250mW Power Dissipation (DIP-8) 650mW Lead temperature (Soldering, 10sec) 260 °C ESD Voltage Protection, Human Body Model 2.5 KV ESD Voltage Protection, Machine Model 250 V Gate Output Current 300mA Caution: Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this s pecification is not implied. Recommended Operating Conditions Item Min. Max. Unit Supply Voltage Vcc 10 24 V Start-up resistor Value 540K 1.8M Ω Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011

Electrical Characteristics

(TA = +25°C unless otherwise stated, VCC=15.0V) PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Voltage (Vcc Pin) Startup Current 12 20 μA VCOMP=0V 1.0 mA VCOMP=3V 2.0 mA OLP Tripped/ Auto 0.47 mA Operating Current (with 1nF load on OUT pin) OVP Tripped /Latch 0.85 mA Holding Current Vcc=7V (latched) 430 μA UVLO (off) 7.5 8.5 9.5 V UVLO (on) 15 16 17 V OVP Level 25 26 27 V Voltage Feedback (Comp Pin) Short Circuit Current V COMP=0V 0.25 mA Open Loop Voltage COMP pin open 5.4 V Green Mode Threshold VCOMP 2.4 V Zero Duty Threshold VCOMP 1.5 V Zero Duty Hysteresis 100 mV Current Sensing (CS Pin) Maximum Input Voltage, VCS_OFF 0.8 0.85 0.9 V Leading Edge Blanking Time 230 ns Internal Slope Compensation 0% to D MAX. (Linearly increase) 300 mV Input impedance 1 M Ω Delay to Output 100 ns Oscillator for Switching Frequency Frequency, FREQ 60 65 70 kHz Green Mode Frequency, FREQG 22 kHz Trembling Frequency ± 4.0 kHz Temp. Stability (-20 °C ~85°C) 5 % Voltage Stability (VCC=11V-25V) 1 % Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 PARAMETER CONDITIONS MIN TYP MAX UNITS Gate Drive Output (OUT Pin) Output Low Level VCC=15V, Io=20mA 1 V Output High Level VCC=15V, Io=20mA 8 V Output High Clamp Level V CC=20V 16 V Rising Time Load Capacitance=1000pF -- 170 350 ns Falling Time Load Capacitance=1000pF 50 100 ns Max. Duty 75 % OLP (Over Load Protection) OLP Trip Level 4.3 4.5 4.7 V OLP Delay Time 55 65 75 ms Brownout Protection (BNO Pin) Brownout Turn-On Trip Level 1.00 1.05 1.10 V Brownout Turn-Off Trip Level 0.75 0.80 0.85 V BNO Pin De-bounce Time 250 us On Chip OTP (Over Temperature) OTP Level 140 °C OTP Hysteresis 30 °C Soft Start Duration Soft Start Duration 2 ms Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Typical Performance Characteristics UVLO (on) (V) Fig. 1 UVLO (on) vs. Temperature Temperature (°C) 14.0 14.8 15.6 16.4 17.2 18.0 -40 0 40 80 120 125 UVLO (off) (V) Temperature (°C) Fig. 2 UVLO (off ) vs. Temperature 6.6 8.2 9.0 10.6 7.4 -40 0 40 80 120 125 9.8 Frequency (KHz) Fig. 3 Frequency vs. T emperature T emperature (°C) -40 60 0 40 80 120 125 Green Mode Frequency (KHz) T emperature (°C) Fig. 4 Green Mode Frequency vs. Temperature -40 0 40 80 120 125 Frequency (KHz) Vcc (V) Fig. 5 Frequency vs. Vcc 12 14 16 18 20 22 24 11 25 Green Mode Frequency (KHz) Vcc (V) Fig. 6 Green Mode Frequency vs. Vcc 12 14 16 18 20 22 2411 25 Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Max Duty (%) Temperature (°C) Fig. 7 Max Duty vs. Temperature -40 0 40 80 120 125 VCS (off) (V) T emperature (°C) Fig. 8 V CS (off) vs. Temperature 0.80 0.82 0.84 0.86 0.88 0.90 -40 0 40 80 120 125 st e Istartup (μA) Temperature (°C) Fig. 9 Startup Current (Istartup) vs. Temperature -40 0 40 80 120 125 VCC OVP (V) Temperature (°C) Fig. 10 VCC OVP vs. Temperature -40 0 40 80 120 125 VCOMP (V) Temperature (°C) Fig. 11 V COMP open loop voltage vs. Temperature -40 0 40 80 120 125 4.0 4.5 5.0 5.5 6.0 6.5 OLP (V) Temperature (°C) Fig. 12 OLP-Trip Level vs. Temperature -40 0 40 80 120 125 3.0 3.5 4.0 4.5 5.0 6.0 Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011

Application Information

The LD7537 meets the green-po wer requirement and is intended for the use in those modern switching power suppliers and adaptors which demand higher power efficiency and power-saving. It integrated more functions to reduce the external components counts and the size. Its major features are described as below. Under Voltage Lockout (UVLO) An UVLO comparator is impl emented in it to detect the voltage on the VCC pin. It would assure the supply voltage enough to turn on the LD7537 PWM controller and further to drive the power MOSFET. As shown in Fig. 13, a hysteresis is built in to prevent the shutdown from the voltage dip during startup. The turn-on and turn-off threshold level are set at 16.0V and 8.5V, respectively. Vcc UVLO(on) UVLO(off) t t I(Vcc) startup current (~uA) operating current (~ mA) Fig. 13 Startup Current and Startup Circuit The typical startup circuit to generate VCC of the LD7537 is shown in Fig. 14. During the startup transient, the V CC is below UVLO threshold. Before it has sufficient voltage to develop OUT pulse to drive the power MOSFET, R1 will provide the startup current to charge the capacitor C1. Once V CC obtains enough voltage to turn on the LD7537 and further to deliver the gate drive signal, it will enable the auxiliary winding of the transformer to provide supply current. Lower startup current requirement on the PWM controller will help to increas e the value of R1 and then reduce the power consumption on R1. By using CMOS process and the special circuit design, the maximum startup current for LD7537 is only 20μA. If a higher resistance value of the R1 is chosen, it will usually take more time to start up. To carefully select the value of R1 and C1 will optimize the power consumption and startup time. EMI Filter OUT CS VCC GND LD7537 AC input Cbulk D1 Fig. 14 Current Sensing and Leading-edge Blanking The typical current mode of PWM controller feedbacks both current signal and voltage signal to close the control loop and achieve regulation. As shown in Fig. 15, the LD7537 detects the primary MOSFET current from 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 0.85V. From above, the MOSFET p eak current can be obtained from below. S )MAX(PEAK R V85.0I = Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Fig. 15 A 230nS leading-edge blanking (LEB) time is included in the input of CS pin to prevent the false-trigger from the current spike. In the low power applications, if the total pulse width of the turn-on spikes is less than 230nS and the negative spike on the CS pin below -0.3V, the R-C filter is free to eliminate. (As shown in Fig.16). However, the total pulse widt h of the turn-on spike is determined according to output power, circuit design and PCB layout. It is strongly recommended to adopt a smaller R-C filter (as shown in Fig. 17) for larger power application to avoid the CS pin being damaged by the negative turn-on spike. Output Stage and Maximum Duty-Cycle An output stage of a CMOS buffer, with typical 300mA driving capability, is incorporated to drive a power MOSFET directly. And the maximum duty-cycle of LD7537 is limited to 75% to avoid the transformer saturation. Voltage Feedback Loop The voltage feedback signal is provided from the TL431 at the secondary side through the photo-coupler to the COMP pin of the LD7537. Similar to UC3842, the LD7537 would carry a diode voltage offset at the stage to feed the voltage divider at the ratio of RA and RB, that is, )VV(RBRA RBV FCOMP)PWM( COMPARATOR −×+=− A pull-high resistor is embedded internally and can be eliminated externally. Fig. 16 Fig. 17 Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Internal Slope Compensation In the conventional applic ations, the problem of the stability is a critical issue fo r current mode controlling, when it operates over 50% duty-cycle. As UC384X, It takes slope compensation from injecting the ramp signal of the RT/CT pin through a coupling capacitor. It therefore requires no extra design for the LD7537 since it has integrated it already. On/Off Control The LD7537 can be turned off by pulling COMP pin lower than 1.5V. The gate output pin of the LD7537 will be disabled immediately under such condition. The off-mode can be released when the pull-low signal is removed. Over Load Protection (OLP) - Auto Recovery To protect the circuit from damage due to over-load condition and short or open-loop condition, the LD7537 is implemented with smart OLP function. It also features auto recovery function; see Fi g. 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 pi n (VCOMP). When the V COMP 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 mechanis m, 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 Switching SwitchingNon-Switching OLP trip Level UVLO(off) OLP Reset Fig. 18 OVP (Over Voltage Protection) on Vcc - Latch mode The Vcc OVP functions of LD7537 are latch mode. Whenever the voltage on the Vcc pin is higher than the OVP threshold, the output gat e drive circuit will be shutdown simultaneous to la tch off the switching of the power MOSFET. As soon as the voltage on Vcc pin drops below OVP threshold and starts AC-recycling again, it will recover to normal operation. Figure 19 shows its operation. F i g . 1 9 Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Brownout Protection The LD7537 programmable to set the brownout protection point though BNO pin. The voltage across the BNO pin is proportional to the bulk capac itor voltage, referred as the line voltage. A brownout co mparator is implemented to detect the abnormal line cond ition. 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 LD537 is implemented with Frequency Swapping function which helps the power supply designers to both optimize EMI performance and lower system cost. The switching frequency substant ially 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 pr otections integrated in the LD7537 to prevent from damage to the power supply. Those damages usually come from open or short conditions on the pins of LD7537. In case under such conditions listed below, the gate output will turn off immediately to protect the power circuit. 1. CS pin floating 2. COMP pin floating Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Reference Application Circuit --- 40W (19V/2.1A) Adapter Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011

Package Information

Dimension in Millimeters Dimensions in Inches Symbol Min Max Min Max A 2.692 3.099 0.106 0.122 B 1.397 1.803 0.055 0.071 D 0.300 0.500 0.012 0.020 F 0.95 TYP 0.037 TYP H 0.080 0.254 0.003 0.010 I 0.050 0.150 0.002 0.006 J 2.600 3.000 0.102 0.118 M 0.300 0.600 0.012 0.024 θ 0° 10° 0° 10° Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011 Dimension in Millimeters Dimensions in Inches Symbol Min Max Min Max A 9.017 10.160 0.355 0.400 B 6.096 7.112 0.240 0.280 D 0.356 0.584 0.014 0.023 E 1.143 1.778 0.045 0.070 F 2.337 2.743 0.092 0.108 I 2.921 3.556 0.115 0.140 J 7.366 8.255 0.29 0.325 Important Notice Leadtrend Technology Corp. reserves the right to make changes or corrections to its products at any time without notice. Custom ers should verify the datasheets are current and complete before placing order. Free Datasheet http://www.nDatasheet.com

Leadtrend Technology Corporation www.leadtrend.com.tw LD7537-DS-01a December 2011

Revision History

Rev. Date Change Notice 00 5/11/2010 Original Specification 01 11/16/2010 Pin Assignment: OTP ÆBNO 01a 12/15/2011 OLP Delay Time (min.) (max.) Operating Ambient Temperature (min.) Free Datasheet http://www.nDatasheet.com