CURRENT MODE PWM CONTROLLER DESCRIPTION SD4870 is a current mode PWM controller IC for high performance, low standby power offline flyback converter application. In no load or light load condition, the IC operates in Light Load Mode to reduce switching loss and improve efficiency. SOT-23-6L Large value startup resistor could be used in the startup circuit to minimize the standby current because of low startup current. SD4870 offers complete protection functions including cycle-bycycle over current protection, over load protection, VDD input voltage over voltage and under voltage protection, etc. DIP-8-300-2.54 SOP-8-225-1.27 Excellent EMI performance is achieved with frequency shuffling technique and soft switching control at the totem pole gate driver output. APPLICATIONS FEATURES * Frequency shuffling to improve EMI performance * Battery Chargers * Light Load Mode for minimum standby power * Adapters * External programmable switching frequency * Set-Top Box Power Supplies * 3uA low startup current * Internal LEB circuit * VDD over voltage and under voltage protection * Gate output maximum voltage clamp * Over current protection * Over load protection * SOT-23-6L/SOP8/DIP8 package ORDERING INFORMATION Part No. Package Marking Material Packing Type SD4870TR SOT-23-6L 4870 Pb free Tape & Reel SD4870A DIP-8-300-2.54 SD4870A Pb free Tube SD4870C SOP-8-225-1.27 SD4870C Pb free Tube SD4870CTR SOP-8-225-1.27 SD4870C Pb free Tape & Reel HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 1 of 8 BLOCK DIAGRAM ABSOLUTE MAXIMUM RATINGS Characteristics Symbol Rating Unit VVDD 25 V VFB -0.3~6 V VSENSE -0.3~6 V VRI -0.3~6 V Junction Temperature Tj -20~150 °C Lead Temperature TL 260 °C Tstg -55~160 °C VDD Voltage FB Voltage SENSE Voltage RI Voltage Storage Temperature HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 2 of 8 ELECTRICAL CHARACTERISTICS (Unless otherwise specified, Tamb=25°C) Characteristics Symbol Test Condition Min. Typ. Max. Unit -- 3 20 μA -- 2 -- mA VDD Startup Current Operation Current IVDD_ST IVDD VDD=12 V,RI=100kΩ VDD=16V, VFB =3V, RI=100kΩ UVLO Threshold Voltage VUVLO 13.3 14.3 15.3 V UVLO Hysteresis Voltage VUVLOH -- 6.3 -- V IVDD =10mA -- 21.5 -- V ΔVFB /ΔVSENSE -- 2 -- V/V 4.5 4.8 5 V 0.8 1 1.2 mA -- 3.8 -- V 35 -- ms 4 6 -- kΩ -- 75 -- % -- 300 -- ns VDD Clamp Voltage VVDD_CLP Feedback PWM Gain AVCS FB Open Loop Voltage VFB_OPEN FB Short Circuit Current IFB_SHORT FB OL Threshold Voltage VFB_OL OL Debounce Time TD_OL FB Input Impedance ZFB_IN Maximum Duty Cycle DMAX FB short connected to ground VDD=16V, RI=100kΩ VFB =3V,VSENSE =0V Current Sense LEB Time SENSE Input Impedance OC Control Delay OC Detection Threshold TLEB RI=100kΩ ZSENSE_IN -- 85 -- kΩ TOC -- 75 -- ns VSENSE_OC 0.7 0.75 0.8 V RI=100kΩ 60 65 70 kHz VDD=12~25V,RI=100kΩ -- 5 -- % RRI_RANGE 50 100 150 kΩ fS_LLM -- 22 -- kHz -3 -- 3 % Switching Frequency Ocsillation Frequency Frequency Stability With VDD RI External Resistance Range Light Load Mode Frequency Frequency Shuffling Range fS ΔfS_VDD ΔfS_SHUF RI=100kΩ Gate Driver Output Low Level VOL VDD=16V, IO=-20mA -- -- 0.8 V Output High Level VOH VDD=16V, IO=20mA 10 -- -- V -- 13 -- V Output Clamp Voltage Level VOH_CLAMP Output Rising Time TR VDD=16V,CL=1nF -- 220 -- ns Output Falling Time TF VDD=16V,CL=1nF -- 70 -- ns HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 3 of 8 PIN CONFIGURATION PIN DESCRIPTIONS Pin No. SD4870 SD4870A Pin Name I/O Description SD4870C 1 8 GND -- Ground. 2 7 FB I Feedback input pin. 3 5 RI I/O 4 4 SENSE I Switch current sense input pin. 5 2 VDD -- Power supply pin. 6 1 GATE O Gate driver output pin. 3,6 NC -- Not connect Oscillator frequency setting pin. A resistor connected between RI and GND. FUNCTION DESCRIPTIONS SD4870 is a current mode PWM controller used in applications for offline flyback converter. The description of functions is as follows. Startup Control Startup current of SD4870 is very low so that IC could start up quickly. A large value startup resistor can be used in startup circuit to minimize standby power loss yet provides reliable startup in application. A 2 MΩ, 1/8 W startup resistor is recommended in normal input range. Frequency Shuffling Control Frequency shuffling is used in SD4870 to improve EMI performance. The oscillation frequency is modulated with a random sourse so that the tone energe is spread out. The spead spectrum minmizes the conduction band EMI and the system design can be easier. The entire application system design can become simpler. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 4 of 8 Light Load Mode In no load or light load condition, major power loss of total power consumption is from switching loss on the MOSFET transistor switching loss, the core loss of the transformer loss and the loss on the external snubber circuit loss become the majority in total power loss. The value of those power loss is proportional to switching actions within a fixed period of time. So reducing number of switching actions leads to reduction of power loss. SD4870 enters Light Load Mode in no load or light load condition. The gate drive output switches only when output DC voltage drops below a present level and the switching frequency reduces. Otherwise the gate drive remains at off state. Oscillation Frequency Setting The oscillation frequency is determined by resistor connected between RI and GND. The relationship between the value of this resistor and frequency are shown below 6500 fS = (kHz) , where RRI is the value of external resistor and its unit is KΩ. RRI Current Sense and LEB At switching leading edge time, the current spike due to Snubber diode reverse recovery should be chopped off. And this is available through internal LEB (Leading Edge Blanking) circuit. So that the external RC filter circuit on SENSE input is no longer required. During the blanking period, the PWM comparator and OC comparator are disabled and MOSFET transistor keeps turn-on state if MOSFET turns on. The minimum on time of MOSFET is LEB time. Gate Drive GATE pin is connected to external MOSFET’s gate for switch control. Too weak the gate drive ability results in more switch loss of MOSFET while too strong gate drive compromises the EMI performance. A good tradeoff is achieved through the totem pole gate drive design with appropriate output ability and dead time control. Protection controls SD4870 offers complete protection functions including cycle-by-cycle over current protection, over load protection, VDD input voltage over voltage and under voltage protection, etc. Constant output power limit over universal input voltage range is achived with over current protection threshold line voltage compensation to over current protection threshold. VDD is supplies by transformer auxiliary winding output. It is clamped when VDD is higher than clamp threshold value. The MOSFET is shut down when VDD drops below UVLO threshold voltage and IC enters power on startup sequence thereafter. When FB input voltage is higher than over load threshold voltage for more than TD_OL, the MOSFET is shut down and VDD voltage drops. IC restarts when VDD is lower than UVLO threshold voltage. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 5 of 8 TYPICAL APPLICATION CIRCUIT HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 6 of 8 PACKAGE OUTLINE DIP-8-300-2.54 UNIT: mm 1.55±0.20 0.3～1.27 3.9±0.3 5.72±0.3 UNIT: mm 6.0±0.4 SOP-8-225-1.27 HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 7 of 8 PACKAGE OUTLINE SOT-23-6L UNIT: mm MOS DEVICES OPERATE NOTES: Electrostatic charges may exist in many things. Please take following preventive measures to prevent effectively the MOS electric circuit as a result of the damage which is caused by discharge: z The operator must put on wrist strap which should be earthed to against electrostatic. z Equipment cases should be earthed. z All tools used during assembly, including soldering tools and solder baths, must be earthed. z MOS devices should be packed in antistatic/conductive containers for transportation. Disclaimer : • Silan reserves the right to make changes to the information herein for the improvement of the design and performance without further notice! • All semiconductor products malfunction or fail with some probability under special conditions. When using Silan products in system design or complete machine manufacturing, it is the responsibility of the buyer to comply with the safety standards strictly and take essential measures to avoid situations in which a malfunction or failure of such Silan products could cause loss of body injury or damage to property. • Silan will supply the best possible product for customers! HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.0 2009.09.22 Page 8 of 8