L4971 1.5A STEP DOWN SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 FEATURES Figure 1. Package UP TO 1.5A STEP DOWN CONVERTER OPERATING INPUT VOLTAGE FROM 8V TO 55V PRECISE 3.3V (±1%) INTERNAL REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 3.3V TO 50V SWITCHING FREQUENCY ADJUSTABLE UP TO 300KHz VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION INTERNAL CURRENT LIMITING (PULSEBYPULSE AND HICCUP MODE) INHIBIT FOR ZERO CURRENT CONSUMPTION PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN SOFT START FUNCTION DIP8 SO16W Table 1. Order Codes Part Number Package L4971 DIP8 L4971D SO16W L4971D013TR SO16 in Tape & Reel A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8V to 55V and output voltages regulated from 3.3V to 50V cover the majority of today’s applications. Features of this new generations of DC-DC converter include pulse-by-pulse current limit, hiccup mode for short circuit protection, voltage feedforward regulation, soft-start, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. The device is available in plastic dual in line, DIP8 for standard assembly, and SO16W for SMD assembly. DESCRIPTION The L4971 is a step down monolithic power switching regulator delivering 1.5A at a voltage between 3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device uses an internal power D-MOS transistor (with a typical Rdson of 0.25Ω) to obtain very high efficency and high switching speed. Figure 1. Block Diagram Vi=8V to 55V 5 8 R1 20K L4971 3 C1 220µF 63V C7 220nF C2 2.7nF C5 100nF 2 4 1 7 R2 9.1K C4 22nF L1 126µH (77120) 6 C6 100nF D1 STPS 3L60U VO=3.3V/1.5A C8 330µF D97IN748A May 2005 Rev. 11 1/13 L4971 Figure 2. Block Diagram VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE 2 SS_INH INHIBIT SOFTSTART 3.3V INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 7 COMP 6 8 FB E/A PWM R 3.3V Q S CBOOT CHARGE AT LIGHT LOADS DRIVE OSCILLATOR 1 3 OSC BOOT 4 GND D97IN594 OUT Figure 3. Pin Connections N.C. 1 16 N.C. GND 2 15 N.C. GND 1 8 FB SS_INH 3 14 FB SS_INH 2 7 COMP OSC 4 13 COMP OSC 3 6 BOOT OUT 5 12 BOOT OUT 4 5 VCC OUT 6 11 VCC N.C. 7 10 N.C. N.C. 8 9 N.C. D97IN595 D97IN596 DIP8 SO16 Table 2. Pin Description DIP SO (*) Name Function 1 2 GND 2 3 SS_INH 3 4 OSC An external resistor connected between the unregulated input voltage and this pin and a capacitor connected from this pin to ground fix the switching frequency. (Line feed forward is automatically obtained) 4 5, 6 OUT Stepdown regulator output 5 11 VCC Unregulated DC input voltage 6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistor 7 13 COMP E/A output to be used for frequency compensation 8 14 FB Ground A logic signal (active low) disables the device (sleep mode operation). A capacitor connected between this pin and ground determines the soft start time. When this pin is grounded disabled the device (driven by open collector/drain). Stepdown feedback input. Connecting directly to this pin results in an output voltage of 3.3V. An external resistive divider is required for higher output voltages. (*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die. 2/13 L4971 Table 3. Absolute Maximum Ratings Symbol Minidip S016 V5 V11 V4 V5,V6 I4 I5,I6 V6-V5 V12-V11 Parameter Input voltage Value Unit 58 V Output DC voltage -1 V Output peak voltage at t = 0.1µs f=200KHz -5 V Maximum output current int. limit. 14 V V6 V12 Bootstrap voltage 70 V V7 V13 Analogs input voltage (VCC = 24V 12 V V2 V3 Analogs input voltage (VCC = 24V) 13 V V8 V14 (VCC = 20V) 6 -0.3 V V DIP8 1 W SO16 0.8 W -40 to 150 °C Ptot Tj,Tstg Power dissipation a Tamb ≤60°C Junction and storage temperature Table 4. Thermal Data Symbol Rth(j-amb) Parameter Thermal Resistance Junction to ambient Max. DIP8 SO16 Unit 90 (*) 110 (*) °C/W (*) Package mounted on board. 3 ELECTRICAL CHARACTERISTCS Table 5. (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125°C Symbol Parameter Test Condition Min. Typ. Max. Unit 55 V DYNAMIC CHARACTERISTIC VI Operating input voltage range Vo = 3.3 to 50V; Io = 1.5A Vo Output voltage Io = 0.5A 3.33 3.36 3.39 V Io = 0.2 to 1.5A 3.292 3.36 3.427 V 3.22 3.36 3.5 V 0.44 0.55 V 0.88 V 3 A Vcc = 8 to 55V Vd Dropout voltage * * 8 Vcc = 10V; Io = 1.5A * Il fs SVRR Maximum limiting current Efficiency Vcc = 8 to 55V * 2 Vo = 3.3V; Io = 1.5A Switching frequency 2.5 85 * 90 100 % 110 60 KHz dB Supply voltage ripple rejection Vi = Vcc+2VRMS; Vo = Vref; Io = 1.5A; f ripple = 100Hz Voltage stability of switching frequency Vcc = 8 to 55V 3 Temp. stability of switching frequency Tj = 0 to 125°C 4 6 % % 3/13 L4971 Table 5. (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125°C Soft Start Soft start charge current 30 40 50 µA Soft start discharge current 6 10 14 µA 0.9 V 5 15 µA 4 6 mA Inhibit VLL Low level voltage * IsLL Isource Low level * DC Characteristics Iqop Iq Iqst-by Total operating quiescent current Quiescent current Duty Cycle = 0; VFB = 3.8V 2.5 3.5 mA Total stand-by quiescent current Vinh <0.9V 100 200 µA Vcc = 55V; Vinh<0.9V 150 300 µA 3.36 3.39 V 5 10 mV Error Amplifier VFB Voltage Feedback Input RL Line regulation 3.33 Vcc = 8 to 55V Ref. voltage stability vs temperature * 0.4 mV/°C VoH High level output voltage VFB = 2.5V VoL Low level output voltage VFB = 3.8V Source output current Vcomp = 6V; VFB = 2.5V 200 300 µA Io sink Sink output current Vcomp = 6V; VFB= 3.8V 200 300 µA Ib Source bias current Io source SVRR E/A gm 10.3 V 0.65 2 3 V µA Supply voltage ripple rejection Vcomp = Vfb; Vcc = 8 to 55V 60 80 dB DC open loop gain RL = ∞ 50 57 dB Transconductance Icomp = -0.1 to 0.1mA Vcomp = 6V 2.5 ms Oscillator Section Ramp Valley Ramp peak 0.78 0.85 0.92 V Vcc = 8V 2 2.15 2.3 V Vcc = 55V 9 9.6 10.2 V 95 97 Maximum duty cycle Maximum Frequency 4/13 Duty Cycle = 0% ; Rosc = 13kΩ, Cosc = 820pF % 300 kHz L4971 Table 6. Typical Performance (Using Evaluation Board) fsw = 100kHz Output Voltage Output Ripple Efficiency Line Regulation VCC =35V IO = 1.5A Io = 1.5A VCC = 8 to 55V Load Regulation VCC =35V IO = 0.5 to 1.5A 3.3V 10mV 84 (%) 3mV 6mV 5.1V 10mV 86 (%) 3mV 6mV 12V 12mV 93 (%) 3mV (VCC =15 to 55V) 4mV Figure 4. Test and valuation board circuit. Vi=8V to 55V 5 8 R1 20K L4971 3 C1 220µF 63V C7 220nF C2 2.7nF 1 7 2 C5 100nF VO=3.3V/1.5A 4 R2 9.1K L1 126µH (77120) 6 C6 100nF C4 22nF D1 ST PS3L60U R3 C8 330µF R4 D97IN749A C1=220µF/63V EKE C2=2.7nF C5=100nF C6=100nF C7=220nF/63V C8=330µF/35V CG Sanyo L1=126µH KoolMu 77120 - 65 Turns - 0.5mm R1=20K R2=9.1K D1=STPS3L60U L4971 VO(V) R3(KΩ) 3.3 0 R4(KΩ) 5.1 2.7 4.7 12 12 4.7 15 16 4.7 18 20 4.7 24 30 4.7 Figure 5. PCB and component layout of the figure 4. 5/13 L4971 Figure 6. Quiescent drain current vs. input voltage. Iq (mA) D97IN724 VO (V) D97IN733 3.377 200KHz R1=22K C2=1.2nF 5 Figure 9. Line Regulation Tj=125˚C 3.376 4 100KHz R1=20K C2=2.7nF 3 0Hz 3.375 Tj=25˚C 3.374 3.373 3.372 2 3.371 Tamb=25˚C 0% DC 3.370 1 0 Figure 7. Quiescent current vs. junction temperature D97IN731 Iq (mA) 200KHz R1=22K C2=1.2nF 5 0 Vcc(V) 5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50 VCC(V) Figure 10. Line Regulation VO (V) 3.378 D97IN734 VCC=35V 3.376 3.374 Tj=25˚C 4 3.372 100KHz R1=20K C2=2.7nF 3.370 Tj=125˚C 3.368 3 0Hz 3.366 VCC=35V 0% DC 2 3.364 3.362 3.360 1 -50 -30 -10 10 30 50 70 90 110 Figure 8. Stand-by drain current vs. input voltage Ibias (µA) D97IN732 Vss=GND 150 0 Tj(˚C) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) Figure 11. Switching frquency vs. R1 and C2 fsw (KHz) D97IN784 500 Tamb=25˚C Tj=25˚C 140 0.8 130 200 120 100 2nF 1.2 nF 2.2 nF 110 Tj=125˚C 100 90 50 3.3n F 4.7n F 20 5.6n 80 F 10 70 60 6/13 0 5 10 15 20 25 30 35 40 45 50 VCC(V) 5 0 20 40 60 80 R1(KΩ) L4971 Figure 12. Switching Frequency vs. input voltage. fsw (KHz) D97IN735 Figure 15. Efficiency vs output voltage. η (%) D97IN737 100KHz 96 107.5 94 105.0 102.5 200KHz 92 Tj=25˚C 90 100.0 VCC=35V IO=1.5A 88 97.5 86 95.0 84 92.5 82 90.0 0 0 5 10 15 20 25 30 35 40 45 50 VCC(V) Figure 13. Switching frequency vs. junction temperature. fsw (KHz) D97IN785 5 10 20 25 VO(V) Figure 16. Efficiency vs. output current. η (%) D97IN738 VCC=8V VCC=12V 90 105 15 85 VCC=24V 80 100 VCC=48V 75 fsw=100KHz VO=5.1V 70 95 65 90 -50 0 50 100 Tj(˚C) Figure 14. Dropout voltage between pin 5 and 4 ∆V (V) 0.5 D97IN736 Figure 17. Efficiency vs. output current. η (%) D97IN739 VCC=8V 90 Tj=125˚C 85 0.4 VCC=12V C 5˚ 2 j= T 0.3 0.2 60 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) Tj=-25˚C VCC=24V 80 VCC=48V 75 70 fsw=100KHz VO=3.36V 0.1 65 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) 60 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) 7/13 L4971 Figure 18. Efficiency vs. output current. D97IN740 η (%) VCC=8V 90 Figure 21. Power dissipation vs. Vcc. Pdiss (mW) D97IN743 VO=5.1V fsw=100KHz VCC=12V 800 VCC=24V 85 IO=1.5A 600 80 IO=1A VCC=48V 75 400 70 fsw=200KHz VO=5.1V 65 60 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) Figure 19. Efficiency vs. output current. η (%) D97IN741 IO=0.5A 200 0 0 10 20 30 50 VCC(V) Figure 22. Efficiency vs. VO Pdiss (mW) D97IN744 VCC=35V fsw=100KHz VCC=8V 90 40 800 85 VCC=12V 80 IO=1.5A 600 VCC=24V 75 IO=1A 400 70 VCC=48V IO=0.5A 65 fsw=200KHz VO=3.36V 200 60 55 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) 0 0 5 10 15 20 25 30 V0(V) Figure 23. Pulse by pulse limiting current vs. junction temperature. Figure 20. Efficiency vs. VCC. η (%) D97IN742 Ilim (A) V0 =5 .1V-f SW =1 V0 85 00KH z .1V W= 20 V0 = 2.8 0K Hz 2.7 3.36 V-f SW = V 0 =3 .36 100 V- fS W= KHz 20 Hz IO=1.5A 2.6 2.5 0K 75 fsw=100KHz VCC=35V 2.9 =5 -fS 80 D97IN747 2.4 70 8/13 2.3 0 10 20 30 40 50 VCC(V) -50 -25 0 25 50 75 100 125 Tj(˚C) L4971 Figure 24. Load transient. Figure 27. Soft start capacitor selection vs. Inductor and Vccmax L (µH) D97IN746 56nF fsw=200KHz 300 47nF 200 33nF 22nF 100 0 15 20 25 30 35 40 45 50 VCCmax(V) Figure 25. Line transient. Figure 28. Open loop frequency and phase of error amplifier VCC (V) D97IN786 30 GAIN (dB) 20 50 D97IN787 Phase GAIN 10 VO (mV) 1 IO = 1A fsw = 100KHz 0 0 -50 45 100 90 -100 2 0 -100 Phase 135 -150 1ms/DIV -200 10 102 103 104 105 106 107 108 f(Hz) Figure 26. Soft start capacitor selection Vs inductor and Vccmax. D97IN745 L (µH) 680nF 470nF fsw=100KHz 400 330nF 300 200 100 220nF 100nF 0 15 20 25 30 35 40 45 50 VCCmax(V) 9/13 L4971 Figure 29. DIP8 Mechanical Data & Package Dimensions mm inch DIM. MIN. A TYP. MIN. 3.32 TYP. MAX. 0.51 B 1.15 1.65 0.045 0.065 b 0.356 0.55 0.014 0.022 b1 0.204 0.304 0.008 0.012 E 0.020 10.92 7.95 9.75 0.430 0.313 0.384 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 F 6.6 0.260 I 5.08 0.200 L Z 3.18 OUTLINE AND MECHANICAL DATA 0.131 a1 D 10/13 MAX. 3.81 1.52 0.125 0.150 0.060 DIP-8 L4971 Figure 30. SO16 Mechanical Data & Package Dimensions mm inch DIM. MIN. TYP. MAX. MIN. TYP. MAX. A 2.35 2.65 0.093 0.104 A1 0.10 0.30 0.004 0.012 B 0.33 0.51 0.013 0.200 C 0.23 0.32 0.009 0.013 D (1) 10.10 10.50 0.398 0.413 E 7.40 7.60 0.291 0.299 e 1.27 0.050 H 10.0 10.65 0.394 0.419 h 0.25 0.75 0.010 0.030 L 0.40 1.27 0.016 0.050 k ddd OUTLINE AND MECHANICAL DATA 0˚ (min.), 8˚ (max.) 0.10 0.004 (1) “D” dimension does not include mold flash, protusions or gate burrs. Mold flash, protusions or gate burrs shall not exceed 0.15mm per side. SO16 (Wide) 0016021 C 11/13 L4971 4 REVISION HISTORY Table 7. Revision History Date Revision October 2004 10 First Issue in EDOCS May 2005 11 Updated the Layout look & feel. Changed name of the D1 on the figs. 1 and 4. 12/13 Description of Changes L4971 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. 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