BM1411 High efficiency 2A Step-Down Converter FEATURES GENERAL DESCRIPTION 2A Output Current The BM1411 is a current-mode step-down DC-DC converter that generates up to 2A output current at 380kHz switching frequency. The device utilizes advanced BCD process for operation with input voltage up to 23V consuming only 20µA in shutdown mode, the BM1411 is highly efficient with peak efficiency at 92% when in operation. Up to 92% Efficiency 4.75V to 23V Input Range 20µA Shutdown Supply Current 380kHz Switching Frequency Adjustable Output Voltage from 1.22V to 0.85·VIN Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Frequency Fold Back at Short Circuit Stability with Wide Range of Capacitors, MSOP-10 Package Protection features include cycle-by-cycle current limit, thermal shutdown, and frequency fold back at short circuit. The BM1411 is available in msop-10 package and requires very few external devices for operation. APPLICATIONS TFT LCD Monitors Portable DVDs Car-Powered or Battery-Powered Equipments Set-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers Termination Supplies 2 4.75V to 18V 4 9 ENABLE BS IN bbm ACmgT4060 CX1411 CX4060 EN G Gnd 6 SW SW FB FB 5 7 2.5V/2A COMP COMP 8 Figure 1. Typical Application Circuit 1 Rev. 1.2 BM1411 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS BM1411 -40°C to 85°C MSOP-10 7,3 N/C PIN CONFIGURATION NC 1 10 NC BS 2 9 EN NC 3 8 COMP IN 4 7 FB SW 5 6 GND BM1411 PIN No. PIN NAME PIN DESCRIPTION 1 NC No Connected 2 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 10nF between this pin and SW. 3 NC No Connected 4 IN Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Application Information section. 5 SW Switch Output. Connect this pin to the switching end of the inductor. 6 G Ground. 7 FB Feedback Input. The voltage at this pin is regulated to 1.22V. Connect to the resistor divider between output and ground to set output voltage. 8 COMP 9 EN Compensation Pin. See Compensation Technique in Application Information section. Enable Input. When higher than 2.0V, this pin turns the IC on. When lower than 1.8V, this pin turns the IC off. Output voltage is discharged when the IC is off. This pin has a small internal pull up current to a high level voltage when pin is not connected. 10 N/C Not Connected. ABSOLUTE MAXIMUM RATINGS 2 Rev. 1.2 BM1411 (Note: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.) PARAMETER VALUE IN Supply Voltage UNIT -0.3 to 23 V SW Voltage -1 to VIN + 1 V BS Voltage VSW - 0.3 to VSW + 6 V EN, FB, COMP Voltage -0.3 to 6 V Continuous SW Current Internally limited A Junction to Ambient Thermal Resistance (θJA) 105 °C/W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C 300 °C Lead Temperature (Soldering, 10 sec) ELECTRICAL CHARCXERISTICS (VIN = 12V, TJ = 25°C unless otherwise specified) PARAMETER SYMBOL TEST CONDITIONS Feedback Voltage VFB 4.75V ≤ VIN ≤ 18V, VCOMP = 1.5V High-Side Switch On Resistance Low-Side Switch On Resistance TYP 1.184 MAX UNIT 1.22 1.258 V RONH 0.22 Ω RONL 4.7 Ω SW Leakage VEN = 0 Current Limit ILIM COMP to Current Limit Transconductance GCOMP Error Amplifier Transconductance GEA Error Amplifier DC Gain AVEA Switching Frequency fSW Short Circuit Switching Frequency Maximum Duty Cycle MIN DMAX 1 2.6 10 µA 3.3 A 1.8 A/V 550 µA/V 3200 V/V 380 430 kHz VFB = 0 50 kHz VFB = 1.1V 90 % ∆ICOMP = ±10µA 330 Minimum Duty Cycle VFB = 1.4V Enable Threshold Voltage Hysteresis = 0.1V 0% 2.0 2.2 V Pin pulled up to 4.5V typically when Enable Pull Up Current left unconnected 2.5 µA Supply Current in Shutdown VEN = 0 20 50 µA IC Supply Current in Operation VEN = 3V, VFB = 1.4V 1.0 1.5 mA Thermal Shutdown Temperature Hysteresis = 10°C 168 3 °C Rev. 1.2 BM1411 1.22V + - Figure 2 . Functional Block Diagram FUNCTIONAL DESCRIPTION As seen in Figure 2, Functional Block Diagram, the BM1411 is a current mode pulse width modulation (PWM) converter. The converter operates as follows: The COMP voltage is the integration of the error between FB input and the internal 1.22V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output. Current limit happens when COMP reaches its maximum clam value of 2.55V. A switching cycle starts when the rising edge of the Oscillator clock output causes the High-Side Power Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected to IN, the inductor current ramps up to store energy in the its magnetic field. The inductor current level is measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when Oscillator clock output goes low, the High-Side Power Switch turns off and the Low-Side Power Switch turns on. At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again. The Oscillator normally switches at 380kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 50kHz at VFB = 0.5V. SHUTDOWN CONTROL The BM1411 has an enable input EN for turning the IC on or off. When EN is less than 1.8V, the IC is in 20µA low current shutdown mode and output is discharged through the Low-Side Power Switch. When EN is higher than 2.0V, the IC is in normal operation mode. EN is internally pulled up with a 2.5µA current source and can be left unconnected for always-on operation. Note that EN is a low voltage input with a maximum voltage of 6V; it should never be directly connected to IN. THERMAL SHUTDOWN The BM1411 automatically turns off when its junction The High-Side Power Switch is driven by logic using BS bootstrap pin as the positive rail. This pin is charged to VSW + 6V when the Low-Side Power Switch turns on. temperature exceeds 168°C. 4 Rev. 1.2 BM1411 Table 1. Typical Inductor Values APPLICATION INFORMATION Vout L(µH) OUTPUT VOLTAGE SETTING 1.5v 6.8 1.8v 6.8 2.5v 10 3.3v 15 5v 22 12v 47 Vout INPUT CAPACITOR R FB1 The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during switching, its ESR also affects efficiency. FB R FB2 The input capacitance needs to be higher than 10µF. The best choice is the ceramic type; however, low ESR tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the output current. The input capacitor should be placed close to the IN and G pins of the IC, with shortest traces possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1µF ceramic capacitor is placed right next to the IC. Figure 3. Output Voltage Setting Figure 3 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the output voltage. Typically, use RFB2 ≈10kΩ and determine RFB1 from the output voltage: ⎛V ⎞ RFB1 = RFB 2 ⎜ OUT − 1⎟ ⎝ 1.22V ⎠ (1 ) OUTPUT CAPACITOR The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: INDUCTOR SELECTION V RIPPLE = IOUTMAX KRIPPLE RESR The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an inductance value L based on ripple current requirement: L= VOUT • (VIN − VOUT ) VIN f SW I OUTMAX K RIPPLE + VIN 28f sw 2 LCOUT (3) where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR resistance of the output capacitor, fSW is the switching frequency, L in the inductor value, COUT is the output capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be used for ceramic type. In the case of tantalum or electrolytic type, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. (2 ) where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. For ceramic output type, typically choose a capacitance of about 22µF. For tantalum or electrolytic type, choose a capacitor with less than 50mΩ ESR. With this inductor value (Table 1), the peak inductor current is IOUT • (1 + KRIPPLE / 2). Make sure that this peak inductor current is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. RECTIFIER DIODE Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode must have current rating higher than the maximum output current and the reverse voltage rating higher than the maximum input voltage. 5 Rev. 1.2 BM1411 STABILTY COMPENSATION COMP CCOMP ＢＭ１４１１ If RCOMP is limited to 15kΩ, then the actual cross over frequency is 3.4 / (VOUTCOUT). Therefore: CCOMP2 RCOMP CCOMP = 1.2 × 10−5VOUT COUT ( F) (11) CCOMP2 in needed only for high ESR output capacitor STEP 3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the cross over frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is: Figure 4. stability compensation The feedback system of the IC is stabilized by the components at COMP pin, as shown in Figure 4. The DC loop gain of the system is determined by the following equation: AVDC = 1.3V IOUT AVEA GCOMP R ESRCOUT ≥ Min ( (4) The dominant pole P1 is due to CCOMP: fP1 = CCOMP 2 = (5) 2π AVBACCOMP The second pole P2 is the output pole: COUTRESRCOUT RCOMP 1 2π RCOMP CCOMP 1 (8) 2π RCOMP CCOMP 2 STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: 2π VOUTCOUTfSW 10GEAGCOMP 1.3V = 1.7 108OUT COUT ( Ω ) (9) but limit RCOMP to 15kΩ maximum. STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. If RCOMP is less than 15kΩ, the equation for CCOMP is: CCOMP = 1.8 10 COUTRESRCOUT (13) RCOMP Table 2. Typical Compensation for Different Output Voltages and Output Capacitors Follow the following steps to compensate the IC: RCOMP = (12) Table 2 shows some calculated results based on the compensation method above. (7) And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): fP 3 = (Ω) Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such as 100pF may improve stability against PCB layout parasitic effects. (6) The first zero Z1 is due to RCOMP and CCOMP: fZ 1 = ) And the proper value for CCOMP2 is: GEA CCOMP 2 = 1.1× 10−6 0.012 × VOUT COUT VOUT COUT RCOMP CCOMP CCOMP2 2.5V 22µF Ceramic 8.2kΩ 2.2nF None 3.3V 22µF Ceramic 12kΩ 1.5nF None 5V 22µF Ceramic 15kΩ 1.5nF None 12V 22µF Ceramic 15kΩ 3.3nF None 2.5V 22µF SP Cap 15kΩ 1.5nF None 3.3V 22µF SP Cap 15kΩ 1.8nF None 5V 22µF SP Cap 15kΩ 2.7nF None 12V 22µF SP Cap 15kΩ 6.8nF None 2.5V 470µF/6.3V/30mΩ 15kΩ 15nF 1nF 3.3V 470µF/6.3V/30mΩ 15kΩ 22nF 1nF 5V 470µF/6.3V/30mΩ 15kΩ 27nF None 12V 220µF/25V/30mΩ 33nF None 15kΩ -5 (F) (10) RCOMP C 6 Rev. 1.2 BM1411 Typical Application 3.3V/2A Output 4 9 IN IN EN ENABLE SW ACT4060 BM1411 G 6 C1 10uF/35V COMP Figure5A: BM1411 3.3V/2A 7 FB 8 C2 22nF R3 15K L1 15uH/3A 5 C5 (optional) 4.75V to 18V C3 10nF 2 BS R2 10K R1 16.9K C4 22uF/10V ceramic,or D1 47uF/6.3 SP cap 3.3V/2A Output Application Typical Application 5.0V/2A Output C3 10nF 2 BS 4 IN IN 9 EN ENABLE BM1411 ACT4060 G 6 C1 10uF/35V Figure5B: SW 5V/2A FB 7 COMP 8 C2 22nF R3 15K BM1411 L1 22uH/3A 5 C5 (optional) 4.75V to 18V 5V/2A 7 R2 10K R1 31K D1 C4 22uF/10V ceramic,or 47uF/6.3 SP cap Output Application Rev. 1.2 BM1411 Typical Application 2.5V/2A Output C3 10nF 10nF 2 4 9 ENABLE ENABLE BS BS IN IN IN IN EN C1 C1 10uF/35V 10uF/35V IC1 CX1411 ACTBMB4060 EN G G 6 SW SW L1 10uH/3A 10uH/3A L1 5 CX4060 FB COMP FB COMP 8 C2 22nF 22nF R3 R3 15K 15K 2.5V/2A 2.5V/2A 7 C5C5 (optional) (optional) 4.75V to to 18V 4.75V 18V R2 R2 10K 10K R1 R1 10.5K D1 10.5K D1 C4 C4 22uF/10V c eramic,or 22uF/10V ceramic,or 47uF/6.3 SP c ap 47uF/6.3 SP cap Figure5C: Figure5CBM: BM1411 CX1411 2.5V/2A 2.5V/2A Output Output Application Application TYPECIAL PERFORMANCE AND CHARACTERISTICS: 8 Rev. 1.2 BM1411 Figure11: PACKAGE OUTLINE MSOP-10 PACKAGE OUTLINE AND DIMENSIONS 9 Rev. 1.2 BM1411 Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.0820 1.100 0.032 0.043 A1 0.020 0.150 0.001 0.006 A2 0.750 0.950 0.030 0.037 b 0.180 0.280 0.007 0.011 c 0.090 0.230 0.004 0.009 D 2.900 3.100 0.114 0.122 e 0.50(BSC) 0.020(BSC) E 2.900 3.100 0.114 0.122 E1 4.750 5.050 0.187 0.199 L 0.400 0.800 0.016 0.031 θ 0 0 6 10 0 0 0 60 Rev. 1.2