® Advanced SP6124 External NMOS PWM Buck Controller FEATURES ■ N-Channel MOSFET Drive ■ Operating Input Voltage: 4.5V - 24V ■ Wide Output Range : 0.8V to 20V ■ ±1.5% 0.8V Reference ■ Low Dropout Operation : 95% Duty Cycle ■ 500KHz Fixed Constant Frequency ■ Low Standby Current, IQ Typ: 720µA ■ Logic-Control Micropower Shutdown ■ Output Overvoltage Protection ■ Internal Diode for Bootstrapped Gate Drive ■ Current Mode Operation for Excellent Line and Load Transient Response ■ Available in 8 pin MSOP package CS 1 8 V IN SP6124 ITH/RUN 2 7 BOOST 8 Pin MSOP FB 3 6 DRI GND 4 5 SW Now Available in Lead Free Packaging APPLICATIONS ■ LCD Monitor ■ PDA ■ Wireless Modems ■ On Card Switching Regulators ■ DC Power Distribution Systems DESCRIPTION The SP6124 is a current mode switching regulator controller that drives an external Nchannel power MOSFET using a fixed frequency architecture. It uses external divider to adjust output voltage from 0.8V to 20V with excellent line and load regulation. A maximum high duty cycle limit of 95% provides low dropout operation which extends operating time in battery-operated systems. Switching frequency up to 500KHz are achievable thus allowing smaller sized filter components. The operating current level is user-programmable via an external current sense resistor. It also provides output overvoltage protection under fault conditions. A multifunction pin (ITH/RUN) allows external compensation for optimum load step response plus shutdown. Soft start can also be implemented with this pin to properly sequence supplies. The SP6124 is available in 8 pin MSOP package. TYPICAL APPLICATION CIRCUIT 1000pF 1 CS 2 ITH/RUN C5 330pF 3 FB SP6124 4 GND ® VIN 8 Boost DRI SW C2 0.1µF 7 6 5 C3 0.1µF R3 24k C4 VIN 6V - 24V C1 RS 33m + M1 FDS6694 D1 SL43 R1 20k CIN1 22µF L1 + CIN2 22µF VOUT 3.3V 3A 10µH COUT 220µF C6 2.2µF 1nF R2 62k CIN1, CIN2: HER-MEI 22µF/35V Electrolytic capacitors M1: FAIRCHILD FDS6694 N -MOSFET D1: GS SL43 L1: TDK SLF12555T-100M3R4 COUT: HER-MEI 220µF /16V Electrolytic capacitor C6: TAIYO YUDEN LMK212BJ225KG -T Ceramic capacitor Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 1 © Copyright 2005 Sipex Corporation ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Supply Voltage (VIN)............................................25V Drive Supply Voltage (BOOST).......................32V Switch Voltage (SW)...........................................25V Differential Boost Voltage (BOOST to SW)........7.0V ITH/RUN, VFB Voltages.......................................8.0V Peak Drive Output Current < 10µs (DRI)...............2A Operating Temperature Range.............-40ûC to +85ûC Storage Temperature Range..............-65ûC to +150ûC Lead Temperature Range (10 sec).....-65ûC to +150ûC Thermal Resistance (TJA) 8 Pin NSOIC...................................................160ûC/W 8 Pin MSOP....................................................180ûC/W ELECTRICAL CHARACTERISTICS Unless otherwise noted, the following specifications apply for VIN = +15V, TA = 25°C. PARAMETER MIN. Input Voltage 4.5 TYP. 720 MAX. UNITS 24 V 900 Input Supply Current CONDITIONS Normal Mode (Note 1) µA Feedback Voltage Output Overvoltage Lockout Shutdown Mode, VITH/RUN = 0V 16 20 0.788 0.8 0.812 V 20 55 90 mV VFB connect to VOUT, ∆ VOVL = VOVL - VFB 0.002 0.015 %/V VIN = 4.5 to 20V 0.7 1.1 Reference Voltage Line Regulation Output Voltage Load Regulation % -0.4 -0.8 ITH Sinking 5µA ITH Sourcing 5µA Run Threshold 0.6 0.8 0.9 V Maximum Current Sense Threshold 125 150 175 mV Oscillator Frequency 45 0 500 550 KHz DRI Rise Time 50 75 ns CLOAD = 3000pF DRI FallTime 50 75 ns CLOAD = 3000pF 5.7 V VIN = 8V, IBOOST = 5mA, SW = 0V VFB = 0.72V Boost Voltage 4.9 5.3 Maximum Duty Cycle 90 94 % Soft Start Time 5 7.5 ms Run Current Source 1.0 2.3 4.0 µA VITH/RUN = 0V, VFB = 0V Run Pullup Current 100 190 250 µA VITH/RUN = 1V Note 1: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 2 © Copyright 2005 Sipex Corporation PIN DESCRIPTION Pin Number Pin Name Description 1 CS 2 ITH/RUN Combination of error amplifier compensation point and run con-trol inputs. The current com-parator threshold increases with this control voltage. Forcing this pin below 0.8V causes the device to be shutdown. 3 FB Feedback error amplifier input, to compare the feedback voltage with the internal reference volt-age. Connecting a resistor R2 to converter output node and a re-sistor R1 to ground yields the out-put voltage: VOUT = 0.8 x (R1+R2)/ R1 4 GND Singal GND for IC. All voltage levels are measured with respect to this pin. 5 SW Switch node connection to induc-tor. In buck converter applications the voltage swing at this pin is from a schottky diode voltage drop below ground to VIN 6 DRI External high-side N-MOSFET gate drive pin. Connect DRI to gate of the external high-side N-MOSFET. 7 BOOST 8 VIN Current sense comparator invert-ing input, not to exceed VIN voltage. Built in offsets between the CS and VIN pins in conjunction with RSENSE set the current trip thresholds. Supply to high-side floating driver. The bootstrap capacitor C3 is returned to this pin. Input voltage pin. It also provides bias to the IC and gate gias for all MOSFETS controlled by the IC. BLOCK DIAGRAM VIN CS VINT VINT VIN R1 + + R2 2.5µA ICOMP Q2 + 40mV - VIN VIN VINT LC_COMP * VIN INTVCC Q1 1.2V Slope * SD LEB Blank Clock Q3 Q4 SS 0.8V + SD 2.4V SD 1.33V + ITH ITH ITH Thermal - FB Date: 01/26/05 DRI Switching Logic Burst_Mode Clock 0.8V R S SW Q VINT Dropout DET VIN T 0.855V Floating Driver + Buffer_ITH + EA - BOOST 1_SHUT M1 * + REF 0.8V FB OSC Slope GND OVDT SP6124, External NMOS PWM Buck Controller 3 © Copyright 2005 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS 100 100 VOUT=3.3V VOUT=5V 95 95 Efficiency (%) VIN=6V Efficiency (%) 90 VIN =12V 85 VIN=19V 80 VIN =6V VIN =12V 90 85 VIN =19V 80 75 75 70 1 10 100 1000 10000 70 Load Current (mA) Fig. 1 Efficiency vs Load Current (VOUT=3.3V) 1 10 100 1000 100 100 VOUT=3.3V 95 VOUT=5V 95 90 85 Efficiency (%) Efficiency (%) 10000 Load Current (mA) Fig. 2 Efficiency vs Load Current (VOUT=5.0V) I LOAD=1A 80 I LOAD=0.1 A 75 90 ILOAD=1A 85 80 ILOAD=0.1A 75 70 0 5 10 15 20 25 30 70 Input Voltage (V) Fig. 3 Efficiency vs Input Voltage 0 10 15 20 25 30 Input Voltage (V) Fig. 4 Efficiency vs Input Voltage 900 7 800 Normal Mode 6 700 Boost Voltage (V) Supply Current ( µA) 5 600 500 40 Shutdown 20 5 10 15 20 25 3 2 VPHASE=0V 0 30 0 Input Voltage (V) Fig. 5 Supply Current vs Input Voltage Date: 01/26/05 VCC=5V 4 1 0 0 VCC=15V 5 5 10 15 20 Boost Load Current (mA) Fig. 6 Boost Load Regulation SP6124, External NMOS PWM Buck Controller 4 © Copyright 2005 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS 7 0.805 0.804 Boost Voltage (V) Reference Voltage (V) VCC UP 6 5 4 3 VCC DOWN 2 IBOOST=2mA 1 VPHASE=0V 0 0.803 0.802 0.801 0.800 0.799 0.798 0.797 0.796 0.795 0.794 0.793 0.792 0.791 0 5 10 15 20 25 30 0.790 -40 Input Voltage (V) Fig. 7 Boost Line Regulation -20 0 20 40 60 80 100 120 140 Temperature (° C) Fig. 8 Reference Voltage vs Temperature 6.0 500 Frequency (KHz) Boost Voltage (V) 480 5.5 5.0 4.5 IBOOST=1mA 460 440 420 VPHASE=0V 4.0 -40 -20 0 20 40 60 80 100 120 400 140 -40 Temperature (° C) Fig. 9 Boost Voltage vs Temperature -20 0 20 40 60 80 100 120 140 Temperature (° C) Fig. 10 Operating Frequency vs Temperature Current Sense Threshold (mV) 160 155 150 145 140 135 130 125 120 -40 -20 0 20 40 60 80 100 120 140 Temperature ( C) Fig. 11 Maximum Current Sense Threshold vs Temperature Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 5 © Copyright 2005 Sipex Corporation APPLICATION INFORMATION Introduction The Main control loop is shutdown when ITH/ RUN goes below 0.8V. When ITH/RUN pulled up to 0.8V or up by error amplifier, main control loop is enabled. The SP6124 is a current mode switching regulator controller that drives external Nchannel power MOSFET with constant frequency architecture. It uses external divider to adjust output voltage with excellent line regulation and load regulation. A maximum high duty cycle limit of 95% provides low dropout operation, which extends operating time in battery-operated system. Low Current Operation During heavy load current operation, SP6124 operates in PWM mode with a frequency of 500KHz. Decreasing of the current will cause a drop in ITH/RUN below 1.33V so that SP6124 enters PFM mode operation for better efficiency. If the voltage across RS does not exceed the offset of current comparator within a cycle, then the high-side and internal MOSFETs will disable until ITH/RUN goes over 1.33V. Wide input voltage ranges from 4.5V to 24V, and switching frequency (500KHz) allows smaller sized filter components. The operating current is user-programmable via an external current sense resistor and it automatically enters PFM operation at low output current to boost circuit efficiency. Component Selection A multifunction pin (ITH/RUN) allows external compensation plus shutdown. A built-in soft start can properly provide sequence supplies. Available packages are in SOP8 and MSOP8 for SMD. SP6124 can be used in many switching regulator applications, such as step-down, step-up, SEPIC and positive-to-negative converters. Of these, the step-down converter is the most common application. External component selection, beginning with selecting RS, depends on the load requirement of the application. Once RS is determined, the choice of inductor, power MOSFET and diode can be easily chosen. Finally, CIN and COUT can be determined. Theory of Operation SP6124 uses a current mode with a constant frequency architecture. Normally the high-side MOSFET turns on each cycle when oscillator sets the RS latch and it turns off when internal current comparator resets the RS latch. Voltage on ITH/RUN pin, which is the output voltage of voltage error amplifier, will control peak inductor current. The output voltage feeds back to VFB pin so that the error amplifier receives a voltage through external resistor divider. When load current increases, it causes a slight decrease in the voltage of VFB pin. Thus the ITH/RUN voltage increases until the average inductor current matches the new load current. While the high-side MOSFET turns off, the low-side MOSFET is turned on to recharge bootstrap capacitor C3. Date: 01/26/05 RS Selection The choice of RS depends on the required output current. The threshold voltage of current comparator decides peak inductor current, which yields a maximum average output current (IMAX). And the peak current is less than half of the peak-to-peak ripple current, ∆IL. Allowing a margin for variation of SP6124, RS can be calculated as follows: R SP6124, External NMOS PWM Buck Controller 6 S = 100mV I MAX © Copyright 2005 Sipex Corporation APPLICATION INFORMATION Inductor Selection Output Diode Selection Since SP6124 operates at a high frequency of 500KHz a smaller inductor value is preferred. In general, operating in high frequency will cause low efficiency because of large MOSFET switching loss. Therefore the effect of inductor value on ripple current and low current operation must be considered as well. In order not to exceed the diode ratings, it is important to specify the diode peak current and average power dissipation. CIN and COUT Selection To prevent high voltage spikes resulting from high frequency switching, a low ESR input capacitor for the maximum RMS current must be used. Usually capacitors may be paralleled to meet size or height requirements in the design. The inductor value has a direct influence on ripple current (∆IL), which decreases with high inductance and increases with high VIN or VOUT: V −V + V V OUT OUT D ÄI = IN ∆ L V +V f ×L D IN The selection of COUT depends on the required effective series resistance (ESR). In general once the ESR requirement is met, the capacitance is suitable for filtering. The output ripple voltage (∆V OUT ) is determined by: VD is the drop voltage of the output Schottky diode. 1 ∆VOUT ≈ ∆I L ESR + 4 fC OUT Accepting a large value of ∆IL allows the use of low inductance, but yields high output ripple voltage and large core loss. The inductor value also has an effect on low current operation. Low inductor value causes the PFM operation to begin at high load current. The efficiency of the circuit decreases at the beginning of low current operation. Generally speaking, low inductance in PFM mode will cause the efficiency to decrease. where f = operating frequency, COUT = output capacitance and ∆IL = ripple current of the inductor. Once the ESR requirement for COUT has been met, the RMS current rating generally exceeds the IRIPPLE(P-P) requirement. Topside MOSFET Driver Supply (C3) External bootstrap capacitor C3 connecting to the BOOST pin supplies the gate drive voltage for highside MOSFET. C3 is charged from INTVCC when SW pin is low. When the high-side MOSFET turns on, the driver places the C3 voltage across the gate and the source of MOSFET. It will enhance the MOSFET and turn on the high-side switch. Then the switch node voltage SW rises to VIN and BOOST pin rises to VIN + INTVCC. In general, 0.1mF is acceptable. Power MOSFET Selection For an application of SP6124, an external N-channel power MOSFET, used as the high-side switch, must be properly selected. To prevent damage to the MOSFET during high input voltage operation, the BVDSS specification of the MOSFET should be considered. Other important selection criteria for the power MOSFET include the “ON” resistance RDS(ON), maximum gate voltage and maximum output current. Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 7 © Copyright 2005 Sipex Corporation APPLICATION INFORMATION Output Voltage Programming Over Current Protection The typical SP6124 application circuit is shown in figure17. A resistive divider, as in the following formula, sets the output voltage. R2 V OUT = 0 .8 V 1 + R1 Over current protection occurs when the peak inductor current reaches maximum current sense threshold divided by sense resistor. The maximum current under over current protection can be calculated by the following formula. 150mV(Maximum current sense threshold) I = MAX The feedback reference voltage 0.8V allows low output voltages from 0.8V to input voltage. A small capacitor at 1nF in parallel to the upper feedback resistor is required for a stable feedback. The ITH/RUN pin, also as a dual-purpose pin, provides loop compensation as well as shutdown function. An internal current source at 2.5mA charges up the external capacitor C5. When the voltage on ITH/ RUN pin reaches 0.8V, the SP6124 begins to operate. Over Voltage Protection Over voltage protection occurs when the FB pin voltage (the negative input of error amplifier) exceeds 0.855V. The over voltage comparator will force driver to pull low until output over voltage is removed. VIN 4.5V - 24V C7 1µF D2 LL4148 S At the same time, the frequency of oscillator will be reduced to sixteenth of original value, 500kHz. This lower frequency allows the inductor current to safely discharge, thereby preventing current runaway. The frequency of oscillator will automatically return to its designed value when the peak inductor value no longer exceeds over current protection point. ITH/RUN Function R4 1.2M R ITH/RUN PCB Layout Since the switching frequency of SP6124 is 500KHz, proper PCB layout and component placement may enhance the performance of SP6124 application circuit. For a better efficiency, major loop from input terminal to output terminal should be as short as possible. In addition, in the case of a large current loop, the track width of each component in the loop should maintain as wide as possible. C5 330pF R3 24k Fig. 12 ITH/RUN pin interfacing Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 8 © Copyright 2005 Sipex Corporation APPLICATION INFORMATION In order to prevent the effect from noise, the GND pin should be placed close to the ground. Also keep the IC’s GND pin and the ground leads at the shortest distance. Recommended layout diagrams and component placement are as shown as figures 13 &16. No sensitive components, which may cause noise interference to the circuit, should be allowed to be close to SW pin. Furthermore, SP6124 is a current mode controller. Keeping the sense resistor close to both VIN and CS pins is recommended for better efficiency and output performance. In addition, all filtering and decoupling capacitors, such as C1 and C2 should be connected as close as possible to SP6124. Fig. 13 Top Layer Fig. 14 Bottom Layer Fig. 15 Placement (Top Overlay) Fig. 16 Placement (Bottom Overlay) Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 9 © Copyright 2005 Sipex Corporation APPLICATION INFORMATION ** VIN 6V~24V R4 1.2M 1 D2 2 LL4148 C7 1µF C5 330pF 3 4 CS ® ITH/RUN SP6124 FB GND VIN Boost DRI SW 1000pF 8 VIN 6V - 24V C1 C2 0.1µF 7 6 5 CIN2 22µF VOUT 3.3V 3A L1 10µH D1 SL43 C4 R1 20k + 22µF M1 FDS6694 C3 0.1µF R3 24k CIN1 + RS 33m COUT 220µF C6 2.2µF 1nF R2 62k Fig. 17: 3.3V Step-Down Converter with external soft start circuit 1 CS ® 2 ITH/RUN C5 330pF C7 3 FB SP6124 VIN 8 1000pF Boost 7 D2 DRI 6 SW 5 4 GND 1nF C2 0.1µF LL4148 R3 24k VIN 5V C1 C3 C4 R1 20k RS 33m + M1 FDS6694 D1 SL43 CIN1 22µF + CIN2 22µF L1 VOUT 3.3V 3A 10µH COUT 220µF C6 2.2µF 1nF R2 62k Fig. 18: 5V to 3.3V Step-Down Converter Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 10 © Copyright 2005 Sipex Corporation PACKAGE: 8 Pin NSOIC D Ø e E/2 L2 E1/2 E1 E Seating Plane L1 1 Gauge Plane VIEW C b INDEX AREA (D/2 X E1/2) Ø L Ø1 TOP VIEW A1 A Seating Plane A2 8 Pin NSOIC JEDEC MO-012 (AA) Variation MIN NOM MAX SYMBOL A 1.35 1.75 A1 0.1 0.25 A2 1.25 1.65 b 0.31 0.51 c 0.17 0.24 4.90 BSC D 6.00 BSC E 3.90 BSC E1 1.27 BSC e L 0.4 1.27 1.04 REF L1 0.25 BSC L2 ø 0º 8º ø1 5º 15º SIDE VIEW B B SEE VIEW C b c Note: Dimensions in (mm) BASE METAL SECTION B-B WITH PLATING Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 11 © Copyright 2005 Sipex Corporation PACKAGE: 8 Pin MSOP D e1 Ø1 E/2 R1 R E1 E Gauge Plane L2 Ø1 Seating Plane Ø L L1 1 2 e Pin #1 indentifier must be indicated within this shaded area (D/2 * E1/2) 8 Pin MSOP JEDEC MO-187 (AA) Variation MIN NOM MAX SYMBOL A 1.1 A1 0 0.15 A2 0.75 0.85 0.95 b 0.22 0.38 c 0.08 0.23 3.00 BSC D 4.90 BSC E 3.00 BSC E1 0.65 BSC e 1.95 BSC e1 L 0.4 0.6 0.8 0.95 REF L1 0.25 BSC L2 N 8 R 0.07 R1 0.07 ø 0º 8º ø1 0º 15º B B A2 A b A1 WITH PLATING b c BASE METAL Note: Dimensions in (mm) Section B-B Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 12 © Copyright 2005 Sipex Corporation ORDERING INFORMATION Part Number Temperature Range Package Types SP6124-EN ...................................................... -40°C to +85°C ................................................... 8-pin NSOIC SP6124-EN/TR ................................................ -40°C to +85°C .................................................. 8-pin NSOIC SP6124-EU ...................................................... -40°C to +85°C .................................................... 8-pin MSOP SP6124-EU/TR ................................................ -40°C to +85°C ................................................... 8-pin MSOP Available in lead free packaging. To order add “-L” suffix to part number. Example: SP6124-1EN/TR = standard; SP6124-EN-L/TR = lead free /TR = Tape and Reel Pack quantity is 2,500 for NSOIC and MSOP. Corporation ANALOG EXCELLENCE Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Date: 01/26/05 SP6124, External NMOS PWM Buck Controller 13 © Copyright 2005 Sipex Corporation