LD7537R 7/01/2010 Green-Mode PWM Controller with Frequency Swapping and Integrated Protections Rev. 00a General Description Features The LD7537R is built-in with several functions, protection z and EMI-improved solution in a tiny package. It takes less High-Voltage CMOS Process with Excellent ESD protection components counts or circuit space, especially ideal for z Very Low Startup Current (<20μA) those total solutions of low cost. 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 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 Applications spending minimum amount of component cost and z Switching AC/DC Adaptor and Battery Charger developing time. z Open Frame Switching Power Supply Typical Application AC input DC Output EMI Filter VCC OUT BNO LD7537R CS COMP GND 1 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw photocoupler LD7537R Pin Configuration SOT-26 (TOP VIEW) COMP NC 8 7 6 OTP GND DIP-8 (TOP VIEW) OUT VCC 5 6 5 37R YWP pp 1 2 TOP MARK 1 2 3 4 OUT VCC NC CS YYWWPP GND YY, Y WW, W PP P37R Ordering Information Part number CS : : : : 4 3 COMP OTP Year code (D: 2004, E: 2005…..) Week code Production code LD7537R Package Top Mark Shipping LD7537R GL SOT-26 Green Package YWP/37R 3000 /tape & reel LD7537R GN DIP-8 Green Package LD7537R GN 3600 /tube /Carton Protection Mode Switching Freq. VCC OVP OLP BNO Pin 65kHz Auto recovery Auto recovery/ 65ms Auto recovery Pin Descriptions SOT-26 DIP-8 NAME 1 8 GND 2 7 COMP FUNCTION Ground Voltage feedback pin (same as the COMP pin in UC384X). Connect a photo-coupler to close the control loop and achieve the regulation. Brownout Protection Pin. Connect a resistor divider between this pin 3 5 BNO and bulk capacitor voltage to set the 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 2 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R Block Diagram ∑ 3 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R 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 -20°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 specification is not implied. Recommended Operating Conditions Item Supply Voltage Vcc Start-up resistor Value Min. Max. Unit 10 24 V 540K 1.8M Ω 4 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R Electrical Characteristics (TA = +25°C unless otherwise stated, VCC=15.0V) PARAMETER CONDITIONS MIN TYP MAX UNITS 12 20 μA Supply Voltage (Vcc Pin) Startup Current VCOMP=0V 1.0 mA Operating Current VCOMP=3V 2.0 mA (with 1nF load on OUT pin) OLP Tripped/ Auto 0.47 mA OVP Tripped/ Auto 0.47 mA 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 VCOMP=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 Leading Edge Blanking Time Internal Slope Compensation 0% to DMAX. (Linearly increase) Input impedance 0.85 0.9 230 ns 300 mV 1 Delay to Output V MΩ 100 ns Oscillator for Switching Frequency Frequency, FREQ 60 Green Mode Frequency, FREQG Trembling Frequency 65 70 kHz 22 kHz ± 4.0 kHz 5 % Temp. Stability (-20°C ~85°C) Voltage Stability (VCC=11V-25V) 1 % Output Low Level VCC=15V, Io=20mA 1 V Output High Level VCC=15V, Io=20mA 8 Rising Time Load Capacitance=1000pF -- Falling Time Output High Clamp Level Gate Drive Output (OUT Pin) 170 350 ns Load Capacitance=1000pF 50 100 ns VCC=20V 16 V 75 % Max. Duty 5 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 V www.leadtrend.com.tw LD7537R PARAMETER CONDITIONS MIN TYP MAX UNITS 4.3 4.5 4.7 V OLP (Over Load Protection) OLP Trip Level 65 OLP Delay Time 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 OTP Level 140 °C OTP Hysteresis 30 °C 2 ms On Chip OTP (Over Temperature) Soft Start Duration Soft Start Duration 6 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R 18.0 10.6 17.2 9.8 UVLO (off) (V) UVLO (on) (V) Typical Performance Characteristics 16.4 15.6 6.6 -40 0 40 Fig. 1 80 120 125 -40 120 125 Fig. 2 UVLO (off ) vs. Temperature 26 Green Mode Frequency (KHz) 66 64 62 60 -40 0 40 80 24 22 20 18 16 120 125 -40 0 40 80 120 125 Temperature (°C) Temperature (°C) Fig. 3 Frequency vs. Temperature Fig. 4 Green Mode Frequency vs. Temperature 25 Green Mode Frequency (KHz) 70 68 Frequency (KHz) 80 Temperature (°C) 68 66 64 62 60 11 40 0 Temperature (°C) UVLO (on) vs. Temperature 70 Frequency (KHz) 8.2 7.4 14.8 14.0 9.0 12 14 16 18 20 22 24 July 2010 17 12 14 16 18 20 22 Fig. 6 Green Mode Frequency vs. Vcc 7 LD7537R-DS-00a 19 Vcc (V) Frequency vs. Vcc Leadtrend Technology Corporation 21 15 11 25 Vcc (V) Fig. 5 23 www.leadtrend.com.tw 24 25 85 0.90 80 0.88 VCS (off) (V) Max Duty (%) LD7537R 75 70 0.86 0.84 0.82 65 60 -40 0 40 80 0.80 -40 120 125 Temperature (°C) Fig. 7 s te VCC OVP (V) Istartup (μA) 120 125 30 12 9 6 25 20 15 3 0 -40 0 Fig. 9 40 80 10 120 125 -40 0 40 80 Temperature (°C) Temperature (°C) Startup Current (Istartup) vs. Temperature Fig. 10 VCC OVP vs. Temperature 6.5 6.0 6.0 5.0 5.5 4.5 OLP (V) VCOMP (V) 80 35 15 5.0 4.5 4.0 40 Temperature (°C) Fig. 8 VCS (off) vs. Temperature Max Duty vs. Temperature 18 0 120 125 4.0 3.5 -40 0 40 80 3.0 120 125 -40 Temperature (°C) 8 LD7537R-DS-00a July 2010 40 80 Temperature (°C) Fig. 12 OLP-Trip Level vs. Temperature Fig. 11 VCOMP open loop voltage vs. Temperature Leadtrend Technology Corporation 0 www.leadtrend.com.tw 120 125 LD7537R Application Information Operation Overview current. Lower startup current requirement on the PWM The LD7537R meets the green-power requirement and is controller will help to increase the value of R1 and then intended for the use in those modern switching power reduce the power consumption on R1. By using CMOS suppliers and adaptors which demand higher power process and the special circuit design, the maximum efficiency and power-saving. It integrated more functions startup current for LD7537R is only 20μA. to reduce the external components counts and the size. If a higher resistance value of the R1 is chosen, it will Its major features are described as below. usually take more time to start up. To carefully select the value of R1 and C1 will optimize the power consumption and startup time. Under Voltage Lockout (UVLO) An UVLO comparator is implemented in it to detect the voltage on the VCC pin. It would assure the supply AC input voltage enough to turn on the LD7537R PWM controller EMI Filter and further to drive the power MOSFET. As shown in Fig. Cbulk D1 13, a hysteresis is built in to prevent the shutdown from R1 the voltage dip during startup. The turn-on and turn-off C1 threshold level are set at 16.0V and 8.5V, respectively. VCC Vcc OUT UVLO(on) LD7537R UVLO(off) CS GND t Fig. 14 I(Vcc) operating current (~ mA) Current startup current (~uA) Sensing and Leading-edge Blanking The typical current mode of PWM controller feedbacks t both current signal and voltage signal to close the control Fig. 13 loop and achieve regulation. As shown in Fig. 15, the Startup Current and Startup Circuit LD7537R detects the primary MOSFET current from the The typical startup circuit to generate VCC of the LD7537R CS pin, which is not only for the peak current mode is shown in Fig. 14. During the startup transient, the VCC control but also for the pulse-by-pulse current limit. The is below UVLO threshold. Before it has sufficient voltage maximum voltage threshold of the current sensing pin is to develop OUT pulse to drive the power MOSFET, R1 will set at 0.85V. From above, the MOSFET peak current can provide the startup current to charge the capacitor C1. be obtained from below. Once VCC obtains enough voltage to turn on the LD7537R IPEAK (MAX ) = and further to deliver the gate drive signal, it will enable the auxiliary winding of the transformer to provide supply 9 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw 0.85 V RS LD7537R V−(PWM COMPARATOR ) = RB × ( VCOMP − VF ) RA + RB A pull-high resistor is embedded internally and can be eliminated externally. 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 width of the turn-on spike is determined according to output power, circuit design and PCB layout. It is strongly recommended to adopt a Fig. 16 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 LD7537R 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 LD7537R. Similar to UC3842, the LD7537R would carry a diode voltage offset at the stage to feed the voltage divider at the ratio of RA and RB, that Fig. 17 is, 10 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R VCC Internal Slope Compensation In the conventional applications, the problem of the UVLO(on) stability is a critical issue for current mode controlling, UVLO(off) when it operates over 50% duty-cycle. As UC384X, It OLP takes slope compensation from injecting the ramp signal of the RT/CT pin through a coupling capacitor. It therefore UVLO(off) OLP Reset t COMP OLP delay time requires no extra design for the LD7537R since it has integrated it already. 4.5V OLP trip Level t On/Off Control OUT The LD7537R can be turned off by pulling COMP pin lower than 1.5V. The gate output pin of the LD7537R will Switching be disabled immediately under such condition. The Non-Switching Switching off-mode can be released when the pull-low signal is t removed. Fig. 18 OVP (Over Voltage Protection) on Vcc Over Load Protection (OLP) - Auto Auto Recovery Recovery The maximum VGS ratings of the power MOSFETs are To protect the circuit from damage due to over-load mostly for 30V. To prevent the VGS enter fault condition, condition and short or open-loop condition, the LD7537R LD7537R series are implemented with OVP function on is implemented with smart OLP function. It also features Vcc. Whenever the Vcc voltage is higher than the OVP auto recovery function; see Fig. 18 for the waveform. In threshold, the output gate drive circuit will be shutdown case of fault condition, the feedback system will force the simultaneously and the switching of the power MOSFET voltage loop toward the saturation and then pull the is disabled until the next UVLO(on). voltage high on COMP pin (VCOMP). When the VCOMP The Vcc OVP functions of LD7537R are auto-recoverable. ramps up to the OLP threshold of 4.5V and continues over If the OVP condition, usually caused by open-loop of OLP delay time, the protection will be activated and then feedback, is not released, the Vcc will tripped the OVP turn off the gate output to stop the switching of power level again and re-shutdown the output. The Vcc works circuit. in hiccup mode. Figure 19 shows its operation. With the protection mechanism, the average input power Otherwise, when the OVP condition is removed, the Vcc will be minimized to remain the component temperature level will be resumed and the output will automatically and stress within the safe operating area. return to the normal operation. 11 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R VCC OVP Tripped OVP Level UVLO(on) UVLO(off) t OUT Switching Non-Switching Switching t 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 Fig. 20 controller to prevent the damage. Figure 20 shows the operation. When VBNO falls below 0.80V, the gate Oscillator and Switching Frequency output will be kept off even Vcc has already achieved UVLO(ON). It therefore makes Vcc hiccup between The LD537R is implemented with Frequency Swapping UVLO(ON) and UVLO(OFF). Unless the line voltage is function which helps the power supply designers to both large enough to pull VBNO larger than 1.05V, the gate optimize EMI performance and lower system cost. The output will not start switching even when the next switching frequency substantially centers at 65KHz, and UVLO(ON) is tripped. A hysteresis is implemented to swap between a range of ±4KHz. prevent the false trigger during turn-on and turn-off. Figure Green-Mode Operation 20 shows the circuit. 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. 12 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R Those damages usually come from open or short conditions on the pins of LD7537R. 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 13 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R Reference Application Circuit --- 40W (19V/2.1A) Adapter 3.15A/250V L N BD1 2 COMP 3 BNO NC BD1 5 VCC CS 4 OUT 6 LD7537R 1 GND D6 RM8 IC432 SMD ZENER1 LD7537R-DS-00a July 2010 www.leadtrend.com.tw +Vo RTN 14 Leadtrend Technology Corporation LD7537R Package Information SOT-26 Symbol Dimension in Millimeters Min Max Min Max A 2.692 3.099 0.106 0.122 B 1.397 1.803 0.055 0.071 C ------- 1.450 ------- 0.057 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° 15 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 Dimensions in Inches www.leadtrend.com.tw LD7537R Package Information DIP-8 Symbol Dimension in Millimeters Dimensions in Inches Min Max Min Max A 9.017 10.160 0.355 0.400 B 6.096 7.112 0.240 0.280 C ----- 5.334 ------ 0.210 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 L 0.381 ------ 0.015 -------- Important Notice Leadtrend Technology Corp. reserves the right to make changes or corrections to its products at any time without notice. Customers should verify the datasheets are current and complete before placing order. 16 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw LD7537R Revision History Rev. Date Change Notice 00 5/11/2010 Original Specification 00a 7/1/2010 Output High Clamp Level Spec. 17 Leadtrend Technology Corporation LD7537R-DS-00a July 2010 www.leadtrend.com.tw