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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. 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. Excellent EMI performance is achieved with frequency shuffling technique and soft switching control at the totem pole gate driver output.
DIP-8-300-2.54 SOP-8-225-1.27 SOT-23-6L
FEATURES
* Frequency shuffling to improve EMI performance * Light Load Mode for minimum standby power * External programmable switching frequency * 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
APPLICATIONS
* Battery Chargers * Adapters * Set-Top Box Power Supplies
ORDERING INFORMATION
Part No. SD4870TR SD4870A SD4870C SD4870CTR Package SOT-23-6L DIP-8-300-2.54 SOP-8-225-1.27 SOP-8-225-1.27 4870 SD4870A SD4870C SD4870C Marking Material Pb free Pb free Pb free Pb free Packing Type Tape & Reel Tube Tube 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 VDD Voltage FB Voltage SENSE Voltage RI Voltage Junction Temperature Lead Temperature Storage Temperature Symbol VVDD VFB VSENSE VRI Tj TL Tstg Rating 25 -0.3~6 -0.3~6 -0.3~6 -20~150 260 -55~160 Unit V V V V C C C
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ELECTRICAL CHARACTERISTICS (Unless otherwise specified, Tamb=25C)
Characteristics VDD Startup Current Operation Current UVLO Threshold Voltage UVLO Hysteresis Voltage VDD Clamp Voltage Feedback PWM Gain FB Open Loop Voltage FB Short Circuit Current FB OL Threshold Voltage OL Debounce Time FB Input Impedance Maximum Duty Cycle Current Sense LEB Time SENSE Input Impedance OC Control Delay OC Detection Threshold Switching Frequency Ocsillation Frequency Frequency Stability With VDD RI External Resistance Range Light Load Mode Frequency Frequency Shuffling Range Gate Driver Output Low Level Output High Level Output Clamp Voltage Level Output Rising Time Output Falling Time VOL VOH VOH_CLAMP TR TF VDD=16V,CL=1nF VDD=16V,CL=1nF VDD=16V, IO=-20mA VDD=16V, IO=20mA -10 -----13 220 70 0.8 ----V V V ns ns fS fS_VDD RRI_RANGE fS_LLM fS_SHUF RI=100k RI=100k VDD=12~25V,RI=100k 60 -50 --3 65 5 100 22 -70 -150 -3 kHz % k kHz % TLEB ZSENSE_IN TOC VSENSE_OC RI=100k ---0.7 300 85 75 0.75 ---0.8 ns k ns V AVCS VFB_OPEN IFB_SHORT VFB_OL TD_OL ZFB_IN DMAX VDD=16V, RI=100k VFB =3V,VSENSE =0V 4 -FB short connected to ground VFB /VSENSE -4.5 0.8 -2 4.8 1 3.8 35 6 75 -5 1.2 ----V/V V mA V ms k % IVDD_ST IVDD VUVLO VUVLOH VVDD_CLP IVDD =10mA VDD=12 V,RI=100k VDD=16V, VFB =3V, RI=100k --13.3 --3 2 14.3 6.3 21.5 20 -15.3 --A mA V V V Symbol Test Condition Min. Typ. Max. Unit
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
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PIN CONFIGURATION
PIN DESCRIPTIONS
Pin No. SD4870 1 2 3 4 5 6 SD4870A SD4870C 8 7 5 4 2 1 3,6 GND FB RI SENSE VDD GATE NC -I I/O I -O -Ground. Feedback input pin. Oscillator frequency setting pin. A resistor connected between RI and GND. Switch current sense input pin. Power supply pin. Gate driver output pin. Not connect Pin Name I/O Description
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 M, 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
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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 K. 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.
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TYPICAL APPLICATION CIRCUIT
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
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PACKAGE OUTLINE
DIP-8-300-2.54 UNIT: mm
SOP-8-225-1.27
UNIT: mm
3.90.3
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
1.550.20
0.31.27
REV:1.0
5.720.3
6.00.4
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: The operator must put on wrist strap which should be earthed to against electrostatic. Equipment cases should be earthed. All tools used during assembly, including soldering tools and solder baths, must be earthed. 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

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