2/21/2005 Green-Mode PWM Controller General Description Features The LD7552 is a low cost, low startup current, current mode High-Voltage CMOS Process with Excellent ESD PWM controller with green-mode power-saving operation. Protection The integrated functions such as the leading-edge blanking Very Low Startup Current (Typical 5 A) of the current sensing, internal slope compensation and the Under Voltage Lockout (UVLO) small package provide the users a high efficiency, minimum Current Mode Control with Cycle-by-Cycle Peak external component counts, and low cost solution for AC/DC Current Limiting power applications. Leading-Edge Blanking on CS Pin Programmable Switching Frequency The special green-mode control does not only achieve low Internal Slope Compensation power consumption but also offer a non-audible-noise Proprietary Green-Mode Control for Power Saving operation when the LD7552 operates under light load or no Non-audible-noise Green Mode Control load condition. 500mA Driving Capability Applications The LD7552 is designed for the switching adaptor with 30W~60W output. The LD7552 is offered in both SOP-8 and Switching AC/DC Adaptor and Battery Charger DIP-8 package. Open Frame Switching Power Supply 384X Replacement Note: Please see Application Information Patent pending Typical Application AC input EMI Filter VCC 40V OUT UVLO 16.0V/ 11.4V RT COMP LD7552 OSC Control Logic Divider photocoupler CS GND 1 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 TL431 Pin Configuration OUT VCC CS NC SOP-8 & DIP-8 (TOP VIEW) 8 7 6 5 YY: Year code (D: 2004, E: 2005…..) WW: week code PP: production code TOP MARK 3 4 RT 2 COMP GND 1 VCC YYWWPP Ordering Information Part number Package TOP MARK Shipping LD7552 IS SOP-8 LD7552IS 2500 /tape & reel LD7552 BS SOP-8 (PB Free) LD7552BS 2500 /tape & reel LD7552 IN DIP-8 LD7552IN 3600 /tube /carton LD7552 BN DIP-8 (PB Free) LD7552BN 3600 /tube /carton Pin Descriptions PIN NAME 1 GND FUNCTION 2 COMP 3 VCC 4 RT 5 NC Unconnected pin 6 CS Current sense pin, connect to sense the MOSFET current 7 VCC Supply voltage pin 8 OUT Gate drive output to drive the external MOSFET Ground Voltage feedback pin (same as the COMP pin in UC384X), By connecting a photo-coupler to close the control loop and achieve the regulation. Supply voltage pin This pin is to program the switching frequency. By connecting a resistor to ground to set the switching frequency. 2 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 Block Diagram VCC UVLO 40V internal bias & Vref 16.0V/ 11.4V RT OSC EN Vref OK EN OUT Green-Mode Oscillator S COMP R 2R R CS Leading Edge Blanking Q PWM Comparator + + Ramp from Oscillator GND Absolute Maximum Ratings Supply Voltage VCC 36V COMP, RT, CS -0.3 ~7V Operating Junction Temperature 150 C Storage Temperature Range -65 C to 150 C Package thermal resistance (DIP-8) 100 C/W Package thermal resistance (SOP-8) 160 C/W Lead temperature (LD7552IS & LD7552IN, Soldering, 10sec) 230 C Lead temperature (LD7552BS & LD7552BN, Soldering, 10sec) 260 C 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. 3 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 Electrical Characteristics o (TA = +25 C unless otherwise stated, VCC=15.0V) PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Voltage (Vcc Pin) Startup Current Operating Current 5 25 A VCOMP=0V 3 4 mA VCOMP=3V 2 VCOMP=open mA 0.7 mA UVLO (off) 10.4 11.4 12.4 V UVLO (on) 14.8 16.0 17.5 V 2.2 3.0 mA Voltage Feedback (Comp Pin) Short Circuit Current VCOMP=0V Open Loop Voltage COMP pin open Green Mode Threshold VCOMP 5.0 V 2.35 V Current Sensing (CS Pin) Maximum Input Voltage 0.80 0.85 0.90 V Leading Edge Blanking Time 250 nS Input impedance 50 K Delay to Output 300 nS Oscillator (RT pin) Frequency RT=100K Green Mode Frequency Fs=66.5KHz 61.5 66.5 71.5 Temp. Stability (-30 C ~85 C) 5 % Voltage Stability (VCC=12V-30V) 2 % 1 V 20 KHz KHz Gate Drive Output (OUT Pin) Output Low Level VCC=15V, Io=20mA Output High Level VCC=15V, Io=20mA Rising Time Load Capacitance=1000pF 160 nS Falling Time Load Capacitance=1000pF 60 nS 4 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 9 V Typical Performance Characteristics 17.0 12.2 16.8 16.4 11.8 UVLO (On) (V) UVLO (Off) (V) 12.0 11.6 11.4 16.0 15.6 15.2 14.8 11.2 14.4 11.0 -40 -20 0 20 40 60 80 100 14.0 -40 120 -20 0 Temperature ( C) Fig. 2 UVLO (Off) vs. Temperature 72.0 18.2 71.0 18.0 Frequency (KHz) Frequency (KHz) Fig. 1 70.0 69.0 68.0 -20 0 20 Fig. 3 40 60 80 100 80 100 120 17.6 17.4 17.0 -40 120 -20 Fig. 4 Frequency vs. Temperature 75.9 75.6 Max. Duty-Cycle (%) 60 17.8 Temperature ( C) 75.3 75.0 74.7 74.4 -40 40 17.2 67.0 66.0 -40 20 Temperature ( C) UVLO (On) vs. Temperature -20 0 20 40 60 80 100 120 Temperature ( C) Fig. 5 Duty-Cycle (max.) vs. Temperature 5 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 0 20 40 60 80 100 120 Temperature ( C) Green-Mode Frequency vs. Temperature Application Information special circuit design, the maximum startup current of Operation Overview LD7552 is only 25 A. The LD7552 is optimized to achieve power saving and minimize the external components counts. The device Theoretically, R1 can be very high resistance value. incorporated several functions to make it ideal to use in However, higher R1 will cause longer startup time. By switching power supplies and switching adaptors. properly select the value of R1 and C1, it can be optimized Under Voltage Lockout (UVLO) under the consideration of R1 power consumption and the An UVLO comparator is included to detect the voltage on startup time. the Vcc pin to ensure the supply voltage enough to power on the LD7552 PWM controller and in addition to drive the power MOSFET. AC input As shown in Fig. 6, a hysteresis is EMI Filter provided to prevent the shutdown from the voltage dip R1 Cbulk during startup. The turn-on and turn-off threshold level are D1 set at 16V and 11.4V, respectively. C1 Vcc VCC UVLO(on) OUT UVLO(off) LD7552 GND t I(Vcc) operating current (~ mA) CS Fig. 7 startup current (~uA) Current Sensing and Leading-edge Blanking The typical current mode PWM controller feedbacks both t current signal and voltage signal to close the control loop Fig. 6 and achieve regulation. As shown in Fig. 8, the LD7552 detects the primary MOSFET current from the CS pin, which Startup Current and Startup Circuit is not only for the peak current mode control but also for the The typical startup circuit as shown in Fig. 7 powers ups the pulse-by-pulse LD7552. threshold of the current sensing pin is set as 0.85V. Thus During the startup transient, the Vcc is lower than the UVLO threshold thus there is no gate pulse generated from LD7552 to drive power MOSFET. current limit. maximum voltage the MOSFET peak current can be calculated as: Therefore, the current through R1 is to provide the startup current as well as charge the capacitor C1. The IPEAK (MAX) Whenever the Vcc voltage is 0 .85 V RS higher enough to power on the LD7552 and further to deliver the gate drive signal, the supply current is provided from the auxiliary winding of the transformer. A 250nS leading-edge blanking time is included in the input The lower of CS pin to prevent the false-trigger caused by the current startup current requirement on the PWM controller will help spike and further to eliminate the need of R-C filter which is to increase the R1 value and then reduce the power usually needed in the typical UC384X application (Fig. 9). consumption on R1. By using CMOS process and the 6 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 Oscillator and Switching Frequency Vin Connecting a resistor from RT pin to GND according to the R1 Cbulk equation can program the normal switching frequency: D1 fSW C1 VCC The suggested operating frequency range of LD7552 is OUT within 50KHz to 130KHz. LD7552 Comp 66.5 100(KHz) RT(K ) CS GND Rs Voltage Feedback Loop The voltage feedback signal is provided from the TL431 in the secondary side through the photocoupler to the COMP Fig. 8 pin of LD7552. The input stage of LD7552, like the UC384X, is with 2 diodes voltage offset then feeding into the voltage divider with 1/3 ratio, that is, 1 ( VCOMP 3 V (PWMCOMPARATOR ) 2 VF ) A pull-high resistor is embedded internally thus can be eliminated on the external circuit. 250ns blanking time VCC Internal Slope Compensation OUT A fundamental issue of current mode control is the stability problem when its duty-cycle is operated more than 50%. To LD7552 stabilize the control loop, the slope compensation is needed in the traditional UC384X design by injecting the ramp signal CS from the RT/CT pin through a coupling capacitor. In LD7552, GND the internal slope compensation circuit has been implemented to simplify the external circuit design. remove On/Off Control Fig. 9 The LD7552 can be controlled to turn off by pulling COMP pin to lower than 1.2V. The gate output pin of LD7552 will Output Stage and Maximum Duty-Cycle be disabled immediately under such condition. The off mode An output stage of a CMOS buffer, with typical 500mA can be released when the pull-low signal is removed. driving capability, is incorporated to drive a power MOSFET directly. And the maximum duty-cycle of LD7552 is limited Dual-Oscillator Green-Mode Operation to 75% to avoid the transformer saturation. There are many difference topologies has been implemented in different chips for the green-mode or power saving requirements such as “burst-mode control”, “skipping-cycle Mode”, “variable off-time control “…etc. The 7 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 basic operation theory of all these approaches intended to By using this dual-oscillator control, the green-mode reduce the switching cycles under light-load or no-load frequency can be well controlled and further to avoid the condition either by skip some switching pulses or reduce the generation of audible noise. switching frequency. What LD7552 used to implement the power-saving "Set" Signal (to OSC & Nor gate) from OSC operation is Leadtrend Technology’s own IP . In such approach, as shown in the block diagram, 2 oscillators are implemented in LD7552. The first oscillator is to take care the normal switching frequency, which can be set by the RT Level-detector & Counter VCO Green-Mode Oscillator Vgreen pin through an external resistor. Under this operation mode, (V+ -Vgreen) >=0, VCO disabled (V+ -Vgreen) <0, VCO activated as shown in Fig. 10, the 2nd oscillation (green-mode oscillator) is not activated. Therefore, the rising-time and the V+ V+ falling-time of the internal ramp will be constant to achieve good stability over all temperature range. Normal Mode Under the normal operation, this oscillator is dominated the switching frequency. Ramp of OSC Green-Mode Osc is not activated under normal operation. OSC Green-Mode Oscillator activated EN=1 EN OUT Green-Mode Osc Ramp of VCO Set Reset 2R R V- R CS S V+ COMP LEB Fig. 11 Q PWM Comparator + + Ramp from Oscillator Note: Patent pending Fig. 10 As shown in Fig. 11, the green-mode oscillator detects the Comp pin signal to determine if it is within the green-mode operation. When the detected signal V+ is lower than the green-mode threshold Vgreen, the green-mode oscillator is on. The green-mode oscillator, implemented by a VCO (voltage controlled oscillator), is a variable frequency oscillator. The rising time of the VCO is proportional to (Vgreen-V+), thus the lower voltage on V+ will generate longer rising time on VCO as well as lower frequency on VCO. 8 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 Vgreen Green Mode V- Package Information SOP-8 H A M J B F C I D Dimensions in Millimeters Dimensions in Inch Symbols 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 0.229 0.007 0.009 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 0° 8° 0° 8° 9 Leadtrend Technology Corporation LD7552-DS-00 February, 2005 DIP-8 A B E J C F 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 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 0.14 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. 10 Leadtrend Technology Corporation LD7552-DS-00 February, 2005