SC4911 Bias/Primary Side PWM Controller with Ultra Low Start-up Current POWER MANAGEMENT Description Features The SC4911 is a highly integrated bias/primary side PWM controller designed for off-line or isolated dc-dc converters in telecommunication and data communication applications. The high degree of integration minimizes the amount of discrete parts needed and leads to substantial cost and space saving converter designs. The circuitry of the SC4911 includes line voltage UVLO featuring startup current less than 50µA and programmable switching frequency. The device supply is derived from an auxiliary winding on the transformer. The auxiliary winding could also provide output feedback information if an optocoupler is not used. Programmable switching frequency up to 500kHz Line UVLO Protection Undervoltage Lockout Low startup current (45µA) Cycle by cycle current limit 8 pin MSOP. Available in Lead-free, fully WEEE and RoHS compliant Applications Telecom isolated converters Offline isolated power supplies Instrumentation power supplies Battery chargers Typical Application Circuit D1 T1 D2 C1 R1 Vout Vin C2 R2 C3 R3 C5 C4 R4 C6 8 VCC ILIM GND C7 OUT COMP 2 R7 U1 SC4911 Q1 7 R6 5 C8 R8 6 4 FB RT 3 LUVLO 1 R5 R9 Revision: April 5, 2006 1 www.semtech.com SC4911 POWER MANAGEMENT Absolute Maximum Ratings Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Parameter Symbol Maximum Units Supply Voltage V CC 18 V Supply Current ICC 20 mA Line UVLO Voltage VCC V FB, ILIM and COMP -0.3 to 6 V 250 mA Output Current Source or Sink Storage Temperature Range TSTG -60 to +150 °C Junction Temperature Range TJ -40 to +150 °C Lead Temperature (Soldering) 10 Sec. TLEAD 260 °C ESD Rating (Human Body Model) ESD 2 kV Electrical Characteristics Unless specified: TA = T = -40°C to +125°C, VCC = 12V, R = 100KΩ, VFB = 2.4V, LUVLO = 1.5V. J Parameter T Test Conditions Min Typ Max Unit 6.0 7.0 V fs = 200kHz, No load 3.4 5.0 mA LUVLO = 0.6V 45 80 µA 15 16 17 V 1.22 1.25 1.28 V Pow er Supply Vcc Turn-On Voltage Operating Current Startup Current VCC Zener Shunt Voltage ICC = 10mA Line UVLO Lockout Threshold UVLO Hysteresis Bias Current VLUVLO < 1.25V 70 mV 100 nA Error Amplifier Feedback Input Voltage Feedback Input Voltage Regulation V C C = 12V 2.44 VCC = 7V to 12V 2.425 2.50 2.56 V 2.575 V Input Bias Current 170 nA Amplifier Transconductance 1000 µmho Amplifier Souce Current 500 µA Amplifier Sink Current 600 µA Open Loop Voltage Gain 50 dB 2006 Semtech Corp. 2 www.semtech.com SC4911 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: TA = T = -40°C to +125°C, VCC = 12V, R = 100KΩ, VFB = 2.4V, LUVLO = 1.5V. J Parameter T Test Conditions Min Typ Max Unit Oscillator Frequency Range RT = 200kΩ 100 RT = 43 kΩ 500 Frequency kHz 170 200 230 kHz 57 65 72 % 0 % 550 mV Duty Cycle Maximum Duty Cycle Minimum Duty Cycle V FB = 3V Current Limit Current Limit Threshold 500 Propagation Delay to Gate 525 70 nS Output Output Voltage Low State Sink 5mA Output Voltage High State Source 5mA Rise Time Fall Time 2006 Semtech Corp. 0.1 V 10.2 V COUT = 100pF 25 nS COUT = 100pF 10 nS 3 9.5 0.5 www.semtech.com SC4911 POWER MANAGEMENT Pin Configuration Ordering Information Part Number TOP VIEW SC4911IMSTR LUVLO VCC RT OUT FB GND COMP ILIM SC4911IMSTRT(2) P ackag e Temp. Range (TJ) MSOP-8(1) -40°C to +125°C Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. (MSOP- 8 PIN) Pin Descriptions Pin # Pin Name Pin Function 1 LUVLO 2 RT For programming oscillator frequency. 3 FB F e e d b a ck. 4 COMP 5 ILIM Current limit sense. 6 GND Ground. 7 OUT Gate drive output. Low during UVLO or LUVLO. 8 VC C Supply voltage. Line under voltage lockout. Feedback compensation. Marking Information Part Number Code (Example: AAxx) yyww = Date Code (Example: 0012) xxxx = Semtech Lot No. (Example: E901 xxxx 01-1) 2006 Semtech Corp. 4 www.semtech.com SC4911 POWER MANAGEMENT Block Diagram Vcc RT L-Uvlo Startup & Uvlo Comp Oscillator Logic BandGap Out + + FB Output Driver - - PWM Latch PWM Comparator Error Amplifier Comp OR gate - ILIM + Ilim Comparator Vt 0 .5 V 0.525V Gnd 2006 Semtech Corp. 5 www.semtech.com SC4911 POWER MANAGEMENT Applications Information The SC4911 is a voltage mode controller designed mainly for the isolated or non-isolated flyback converters. As shown in the Block Diagram, it includes start-up circuit, bandgap, error amplifier, PWM comparator, logic and output stage. Line undervoltage has dual functions of line voltage lockout and shutdown. When LUVLO is pull down to ground, the SC4911 is disabled and the quiescent current is reduced to typical 30µA. When it is connected to a resistor voltage divider between input voltage and ground, it monitors the line voltage. The bias current consumed by the device during this period is only typical 30µA. Once Vcc exceeds the turn-on voltage, OUT starts driving the MOSFET, transferring energy to the secondary and the bias output. If the bias output voltage builds to and is above the Vcc turnoff voltage, the start-up is completed and normal operation begins. The size of the start-up resistor not only affects power supply start-up time, but also power supply efficiency. The resistor dissipates continuous power in normal operation. Due to ultra low start-up current of the SC4911, large value resistor (several hundred Kohm to 1Mohm) could be used, particularly for off-line applications to improve efficiency considering reasonable start-up time. Oscillator The switching frequency of the SC4911 is set by an external resistor connected between RT and GND. Figure 1 shows the relationship between the resistance of the external resistor and the switching frequency. Current Limit The current sense resistor is selected by dividing the current sense threshold voltage 0.525V by the primary peak current at the desired current limit point, typically 120% of the primary peak current. Figure 1. Timing Resistor vs Oscillator Frequency Timing Resistor vs Switching Frequency R SENSE = Resistance ( Kohms ) 250 200 Care must be taken to ensure proper selection of sense resistor and good layout to prevent erratic operation. The non-inductive resistor must be used as the sense resistor. Parasitic inductance in series with the sense resistor must be minimized. Additional RC filter may be necessary to eliminate the narrow spike time on the leading edge of the primary current. The RC time constant can be chosen to be equal to the time constant of the sense resistor and the parasitic inductance. 150 100 50 0 100 200 300 400 500 Frequency ( KHz ) Line UVLO and VCC UVLO The Line UVLO monitors the input line voltage and VCC UVLO monitors the supply voltage to the SC4911. If either input line or VCC is below the lockout threshold, the output is held low and the supply current to the chip is typically 30µA. A resistor divider from the input line to GND determines the desired undervoltage lockout level. To prevent noise coupling to affect proper UVLO operation, a small capacitor, one hundred to a few hundred pF, is recommended to be used from Line UVLO pin to GND. PCB Layout Long power supply and ground traces should be avoided. A 0.1µF ceramic capacitor closely placed between Vcc and GND is recommended. The timing resistor used to program switching frequency should be located close to pin RT and pin GND in order to have a stable switching frequency. MOSFET should be located near the device and a resistor in the range of several ohms could be used in series with the gate drive to damp the ringing if the trace between the drive output and MOSFET is not short enough. Star ground connection is recommended to avoid ground loops. The Power path for input filter, MOSFET and transformer should be separated from signal path for timing resistor and feedback resistor, and both should be brought to a single ground point. Start-up As shown in Typical Applications Circuit on the front page, when input voltage is applied, C1 is trickle charged through the start-up resistor R1 until the SC4911 Vcc reaches the turn-on voltage. 2006 Semtech Corp. 0.525 V 1.2 × IPK 6 www.semtech.com SC4911 POWER MANAGEMENT Typical Applications 48V TO 12V FLYBACK CONVERTER AS AUXILIARY SUPPLY The output of the T1 bias winding is rectified, filtered by C1 and is fed to the FB through feedback resistor R5 and R7. The output voltage on the secondary is proportional to the bias voltage by the turns ratio of the output to the bias winding. C7 and R9 are for frequency compensation. An additional small capacitor could be used from COMP to GND if it is needed. The LUVLO pin monitors the input voltage via resistor R2 and R4 to determine turn-on and turn-off of the converter. Capacitor C5 helps filter out the noise from the input line. Figure 2 shows a simple bias supply using the SC4911. This 36 - 72V input flyback power supply employs primary side regulation from the transformer bias winding, which eliminates the need of opto coupler and secondary reference error amplifier. This is best for low cost applications requiring isolation and narrow load variation range on the secondary. During the start-up, the input source trickle charges the capacitor C1 through start-up resistor R1. As long as voltage across C1 reaches the Vcc turn-on threshold, the SC4911 turns on abruptly and start driving the gate of MOSFET Q1. After the SC4911 starts up the primary bias winding supplies the primary circuitry. Vpri = 12V D1 1N5819 C1 10uF R1 100K Vin = 48V 2 T1 D2 1N5819 1 8 3 R2 2.7MEG C3 10uF R5 383K C5 100pF R3 68 C4 0.1uF R4 100K 1 8 LUVLO 3 4 R7 100K C7 47nF R9 4.7K 5 C6 150pF VCC OUT COMP ILIM RT C2 100uF U1 SC4911 FB 2 10 Vo = 12V Q1 Si2320DS 7 5 R6 51 C8 1000pF GND 6 R8 1.00 R10 100K Figure 2. 48V to 12V Flyback Converter as Auxiliary Supply 2006 Semtech Corp. 7 www.semtech.com SC4911 POWER MANAGEMENT Typical Applications (Cont.) Isolated feedback 48V to 12V application Figure 3 gives an example of isolated feedback and low power flyback application of the SC4911. T1 is a three winding transformer. The winding 1-2 is a bias winding which supplies the primary circuitry after the SC4911 starts up. During the startup, the input source trickle charges the capacitor C1 through the start-up resistor R1. As long as voltage across C1 reaches the Vcc turnon threshold, the SC4911 turns on abruptly and start driving the gate of MOSFET Q1. As Q1 starts switching, regenerative feedback from the bias winding will provide current via D1 to capacitor C1. In this configuration, the input voltage is in the range of 36V to 72V for telecom applications, and the LUVLO pin monitors the input voltage via resistor R2 and R5 to determine turn-on and turn-off of the converter. Capacitor C5 helps filter out the noise from the input line. D1 1N5819 C1 10uF R1 100K Vin = 48V Timing resistor R13 sets switching frequency. R3 and C6 are used to suppress the voltage spikes across the switch due to leakage inductance of T1. R11 is current sense resistor to set current limit of the convertor. R10 and C9 filter spikes caused by parasitic capacitance during the turning on of Q1. The U3 SC431 is shunt regulator integrating an accurate 2.5V bandgap reference, op amp and driver into a single device. It compares sensed output voltage divided by R7 and R9 to its internal reference and drives the amplified error signal to opto-coupler U1. C7 keeps ripple and noise from over driving the device. U1 delivers the isolated feedback signal to the SC4911. C8 and R12 are for compensation. An additional small capacitor could be used from COMP to GND if needed. T1 2 1 8 Vo = 5V D2 1N5819 C2 100uF 3 10 C3 10uF R2 2.7MEG C5 100pF R3 68 C4 0.1uF R5 100K 1 8 LUVLO 3 4 U2 SC4911 OUT COMP U1 NEC2501 C6 150pF VCC FB 5 ILIM 5 U3 SC431 R8 1K R10 R6 1K C7 Q1 Si2320DS 7 R4 330 R7 10K 220pF R9 10K 51 C8 RT 47nF R12 4.7K 2 GND 6 C9 1000pF R11 1.00 R13 100K Figure 3. Isolated 48V to 12V Flyback Converter 2006 Semtech Corp. 8 www.semtech.com SC4911 POWER MANAGEMENT Typical Applications (Cont.) Non-Isolated feedback 48V to 12V application Figure 4 is an example of low cost, non-isolated feedback, low power application of the SC4911. T1 is a two winding transformer. The output voltage is directly fed to the primary circuitry. In this 36V to 72V telecom application, LUVLO monitors the input voltage via resistor R2 and R4 to determine turn-on and turn-off of the converter. Capacitor C4 helps filter out the noise from the input line. Voltage feedback is directly brought from the output to the input error amplifier of SC4911 through R5 and R7. C6 and R9 are for frequency compensation. An additional small capacitor could be used from COMP to GND if needed. During the start-up, the input source trickle charges the capacitor C3 through start-up resistor R1. As long as the voltage across C3 reaches the Vcc turn-on threshold, the SC4911 turns on abruptly and starts driving the gate of MOSFET Q1. After the SC4911 starts up the secondary winding supplies the primary circuitry. D1 1N5819 R1 100K Vin = 48V T1 R2 2.7MEG C2 10uF R5 383K C4 100pF 4 R7 100K C3 10uF C5 150pF 8 U1 SC4911 1 LUVLO VCC 3 FB OUT COMP ILIM C6 47nF RT 2 R9 4.7K C1 47uF R3 68 R4 100K Q1 Si2320DS 7 5 Vo = 12V D2 1N5819 R6 51 GND C7 1000pF 6 R8 1.00 R10 100K Figure 4. Non-isolated 48V to 12V Flyback Converter 2006 Semtech Corp. 9 www.semtech.com SC4911 POWER MANAGEMENT Typical Applications (Cont.) 48V to 12V FLYBACK CONVERTER AS BATTERY CHARGER In this application, voltage feedback is directly brought from the output to the input error amplifier of SC4911 through R4 and R7. C5 and R9 are for frequency compensation. Figure 5 is another example of non-isolated feedback, low power and compact application of the SC4911 as a battery charger. Battery charging rate is determined by current sense resistor R8. LUVLO is used to not only turn on or turn off the charger by battery charge controller, but also monitors the input line voltage via resistor R2 and R5 to determine turn-on and turnoff of the converter. During the start-up, the input source trickle charges the capacitor C3 through start-up resistor R1. As long as voltage across C3 reaches the Vcc turn-on threshold, the SC4911 turns on abruptly and starts driving the gate of MOSFET Q1. After the SC4911 starts up the secondary winding supplies the primary circuitry. D1 1N5819 R1 100K Vin = 48V C2 10uF R2 2.7MEG R4 619K C3 10uF R5 100K 1 To Battery Charger Controller 8 T1 4 R7 100K C5 47nF C4 150pF U1 SC4911 R9 4.7K FB OUT COMP ILIM RT 2 C1 47uF R3 68 LUVLO VCC 3 To 12V Battery D2 1N5819 GND 6 Q1 Si2320DS 7 5 R6 51 C6 1000pF R8 1.00 R10 100K Figure 5. 48V to 12V Flyback Converter as Battery Charger 2006 Semtech Corp. 10 www.semtech.com SC4911 POWER MANAGEMENT Evaluation Board Schematic D1 1N5819HW J3 Vb=12V 1 2 Vin=48V C1 47uF D3 1N5819HW J2 1 2 T1 2 31414R 1 5 3 C4 10uF/100V R2 2.7MEG R5 383K C6 470pF R1 100K R3 68 C5 10uF R4 100K 1 8 4 R8 100K C10 470pF R10 4.99K 2006 Semtech Corp. OUT COMP ILIM C8 47nF 2 C3 47uF 1 2 Vo=12V 4 U1 SC4911 FB RT 8 C2 47uF C7 150pF/100V LUVLO VCC 3 J1 D2 B150 GND 7 Q1 Si2320DS R6 0 5 R7 51 C9 1000pF 6 R9 1.00 R11 100K 11 www.semtech.com SC4911 POWER MANAGEMENT Evaluation Board Schematic- BOM Item Quantity Reference Part/Description Manufacturer # Foot Print 47uF 16TPB47M SM/CT 7343 1 3 C 1, C 2, C 3 2 1 C4 10uF/100V EEU-FC2A100 CYL/D.250/LS.100/.031 3 1 C5 10uF GRM32ER61C106KC31L SM/C 1210 4 1 C6 470pF SM/C 0805 6 1 C7 150pF/100V SM/C 0805 6 2 C 8, C 10 47nF SM/C 0805 7 1 C9 1000pF SM/C 0805 8 2 D 1, D 3 1N5819HW SOD123 9 1 D2 B150-13 SM/SMA 10 1 Q1 S i 2320D S 11 4 R1, R4, R8, R11 12 1 13 Si2320DS-T1 SOT-23 100K SM/R 0805 R2 2.7 MEG SM/R 0805 1 R3 68 SM/R 0805 14 1 R5 383K SM/R 0805 15 1 R6 0 SM/R 0805 16 1 R7 51 SM/R 0805 17 1 R9 1 SM/R 0805 18 1 R10 4.99K SM/R 0805 19 1 T1 31414R MIDCOM 31414R 20 1 U1 SC4911IMSTR Semtech Corp. 805-498-2111 MSOP-8 2006 Semtech Corp. 12 www.semtech.com SC4911 POWER MANAGEMENT Typical Characteristics Oscillator Frequency vs Temperature Vcc Turn-On Voltage vs Temperature 5.70 Frequency (kHz) Turn On Voltage (V) 5.80 5.60 5.50 5.40 5.30 5.20 5.10 -40 -20 0 20 40 60 80 100 200.00 199.00 198.00 197.00 196.00 195.00 194.00 193.00 192.00 191.00 190.00 Rt = 100k -40 120 -20 0 Temperature (°C) 60 80 100 120 Line UVLO Lockout Threshold vs Temperature 16.04 1.245 16.02 1.244 Lockout Threshold (V) Zener Shunt Voltage (V) 40 Temperature (°C) Vcc Zener Shunt Voltage vs Temperature 16.00 15.98 15.96 15.94 15.92 15.90 1.243 1.242 1.241 1.240 1.239 1.238 1.237 1.236 -40 -20 0 20 40 60 80 100 120 -40 -20 0 Temperature (°C) 20 40 60 80 100 120 Temperature (°C) Max. Duty Cycle vs Temperature Error Amplifier Feedback Voltage vs Temperature 66.50 2.525 Feedback Input Voltage (V) Max. Duty Cycle (%) 20 66.00 65.50 65.00 64.50 64.00 63.50 63.00 -40 -20 0 20 40 60 80 100 2.520 2.515 2.510 2.505 2.500 2.495 2.490 120 -40 Temperature (°C) -20 0 20 40 60 80 100 120 Temperature (°C) Current Limit Threshold vs Temperature 528 Threshold (mV) 527 526 525 524 523 522 521 520 -40 -20 0 20 40 60 80 100 120 Temperature (°C) 2006 Semtech Corp. 13 www.semtech.com SC4911 POWER MANAGEMENT Outline Drawing - MSOP-8 e/2 DIM A A A1 A2 b c D E1 E e L L1 N 01 aaa bbb ccc D N 2X E/2 E1 PIN 1 INDICATOR ccc C 2X N/2 TIPS E 1 2 e B D aaa C SEATING PLANE .043 .000 .006 .030 .037 .009 .015 .009 .003 .114 .118 .122 .114 .118 .122 .193 BSC .026 BSC .016 .024 .032 (.037) 8 0° 8° .004 .005 .010 1.10 0.00 0.15 0.95 0.75 0.22 0.38 0.08 0.23 2.90 3.00 3.10 2.90 3.00 3.10 4.90 BSC 0.65 BSC 0.40 0.60 0.80 (.95) 8 0° 8° 0.10 0.13 0.25 H A2 A c GAGE PLANE A1 bxN bbb C A-B D C DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX 0.25 L DETAIL SEE DETAIL SIDE VIEW 01 (L1) A A NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MO-187, VARIATION AA. Land Pattern - MSOP-8 X DIM (C) G C G P X Y Z Z Y DIMENSIONS INCHES MILLIMETERS (.161) .098 .026 .016 .063 .224 (4.10) 2.50 0.65 0.40 1.60 5.70 P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804 2006 Semtech Corp. 14 www.semtech.com