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L4978 2A STEP DOWN SWITCHING REGULATOR 1 Features UP TO 2A 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 Figure 1. Packages DIP-8 SO16W Table 1. Order Codes Part Number L4978 L4978D L4978D013TR Package DIP-8 SO16 SO16 in Tape & Reel efficency and high switching speed. 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 DCDC 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. 2 DESCRIPTION The L4978 is a step down monolithic power switching regulator delivering 2A 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 0.25) to obtain very high Figure 2. Typical Application Circuit Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7 8 L4978 4 1 6 L1 126H (77120) D1 ST PS3L60U C8 330F VO=3.3V/2A C5 100nF R2 9.1K C4 22nF C6 100nF D98IN837A May 2005 Rev. 9 1/13 L4978 Table 2. Block Diagram VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE SS_INH 2 INHIBIT SOFTSTART 3.3V COMP FB 7 8 E/A INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 6 PWM BOOT R S 3.3V Q DRIVE OSCILLATOR 1 GND CBOOT CHARGE AT LIGHT LOADS 3 OSC 4 OUT D97IN594 Figure 3. Pins Connection (Top view) N.C. GND GND SS_INH OSC OUT 1 2 3 4 D97IN595 1 2 3 4 5 6 7 8 D97IN596 16 15 14 13 12 11 10 9 N.C. N.C. FB COMP BOOT VCC N.C. N.C. 8 7 6 5 FB COMP BOOT VCC SS_INH OSC OUT OUT N.C. N.C. DIP-8 SO16W Table 3. Pin Description N 1 2 Pin 2 3 Name GND SS_INH 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 disables the device (driven by open collector/drain). 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) Function 3 4 OSC 2/13 L4978 Table 3. Pin Description (continued) N 4 5 6 7 8 Pin 5, 6 11 12 13 14 Name OUT VCC BOOT COMP FB Stepdown regulator output Unregulated DC input voltage A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistors E/A output to be used for frequency compensation 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. Function (*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die. Table 4. Thermal Data Symbol Rth(j-amb) (*) Package mounted on board. Parameter Thermal Resistance Junction to ambient Max. Minidip 90 (*) SO16 110 (*) Unit C/W Table 5. Absolute Maximum Ratings Symbol Parameter Minidip V5 V4 I4 V6-V5 V6 V7 V2 V8 Ptot S016 V11 V5,V6 I5,I6 V12-V11 V12 V13 V3 V14 Bootstrap voltage Analogs input voltage (VCC= 24V) Analogs input voltage (VCC= 24V) (VCC= 20V) Power dissipation a Tamb 60C DIP-8 SO16 Junction and storage temperature 1 0.8 -40 to 150 W W C Input voltage Output DC voltage Output peak voltage at t = 0.1ms f=200KHz Maximum output current 14 70 12 13 6 -0.3 58 -1 -5 int. limit. V V V V V V V V V Value Unit Tj,Tstg 3/13 L4978 Table 6. Electrical Characteristcs (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 24V, unless otherwise specified). "" Specification Referred to Tj from 0 to 125C Symbol VI Vo Parameter Operating input voltage range Output voltage Test Condition Vo = 3.3 to 50V; Io = 2A Io = 0.5A Min. 8 3.33 3.292 Typ. Max. 55 Unit V V V V V V A % KHz dB DYNAMIC CHARACTERISTIC 3.36 3.36 3.36 0.58 3.39 3.427 3.5 0.733 1.173 3.5 110 Io = 0.2 to 2A Vcc = 8 to 55V Vd Dropout voltage Maximum limiting current Efficiency fs SVRR Switching frequency Supply voltage ripple rejection Switching Frequency Stability vs. Vcc Temp. stability of switching frequency SOFT START Soft start charge current Soft start discharge current INHIBIT VLL IsLL Iqop Iq Iqst-by Low level voltage Isource Low level Total operating quiescent current Quiescent current Total stand-by quiescent current Duty Cycle = 0; VFB= 3.8V Vinh < 0.9V Vcc = 55V; Vinh<0.9V 3.22 Vcc = 10V; Io = 2A Vcc = 8 to 55V Vo = 3.3V; Io= 2A Il 2.5 90 60 3 87 100 Vi = Vcc+2VRMS; Vo= Vref; Io = 2.5A; f ripple= 100Hz Vcc = 8 to 55V Tj = 0 to 125C 3 4 6 % % 30 6 40 10 50 14 0.9 A A V A mA mA A A V mV mV/C V 5 4 2.5 100 150 3.33 3.36 5 0.4 10.3 15 6 3.5 200 300 3.39 10 DC CHARACTERISTICS ERROR AMPLIFIER VFB RL Voltage Feedback Input Line regulation Ref. voltage stability vs temperature VoH VoL Io source Io sink Ib SVRR E/A High level output voltage Low level output voltage Source output current Sink output current Source bias current Supply voltage ripple rejection DC open loop gain gm Transconductance Vcomp = VFB; Vcc = 8 to 55V RL = Icomp = -0.1 to 0.1mA Vcomp = 6V 60 50 VFB = 2.5V VFB = 3.8V Vcomp= 6V; VFB= 2.5V Vcomp = 6V; VFB= 3.8V 180 200 220 300 2 80 57 2.5 3 Vcc = 8 to 55V 0.65 V A A A dB dB mS 4/13 L4978 Table 6. Electrical Characteristcs (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 24V, unless otherwise specified). "" Specification Referred to Tj from 0 to 125C Symbol Parameter Ramp Valley Ramp peak Maximum duty cycle Maximum Frequency Duty Cycle = 0% Rosc = 13k, Cosc = 820pF Vcc = 8V Vcc = 55V Test Condition Min. 0.78 2 9 95 Typ. 0.85 2.15 9.6 97 300 Max. 0.92 2.3 10.2 Unit V V V % kHz OSCILLATOR SECTION Figure 4. Test and evaluation board circuit. Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7 8 L4978 4 1 6 L1 126H (77120) C8 330F VO=3.3V/2A R3 C5 100nF R2 9.1K C4 22nF C6 100nF D1 STPS3L60U R4 D98IN834B C1=220F/63V EKE C2=2.7nF C5=100nF C6=100nF C7=220nF/63V C8=330F/35V CG Sanyo L1=126H KoolMu 77120 - 55 Turns - 0.5mm R1=20K R2=9.1K D1=STPS3L60U L4978 VO(V) 3.3 5.1 12 15 18 24 R3(K) 0 2.7 12 16 20 30 4.7 4.7 4.7 4.7 4.7 R4(K) Figure 5. PCB and component layout of the figure 4. 5/13 L4978 Figure 6. Quiescent drain current vs. input voltage. Iq (mA) 200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF D97IN724 Figure 9. Line Regulation . VO (V) 3.377 Tj=125C D97IN733 5 3.376 3.375 Tj=25C 4 3.374 3 0Hz 3.373 3.372 2 Tamb=25C 0% DC 3.371 3.370 1 0 5 10 15 20 25 30 35 40 45 50 Vcc(V) 0 5 10 15 20 25 30 35 40 45 50 VCC(V) Figure 7. Quiescent current vs. junction temperature Iq (mA) 5 D97IN731 Figure 10. Load regulation . VO (V) 3.378 3.376 3.374 3.372 3.370 3.368 Tj=125C Tj=25C D98IN835 VCC=35V 200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF 0Hz 4 3 VCC=35V 0% DC 3.366 3.364 3.362 2 1 -50 -30 -10 10 30 50 70 90 110 Tj(C) 3.360 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A) Figure 8. Stand by drain current vs. input voltage. Ibias (A) 150 140 130 120 110 100 90 80 70 60 0 5 10 15 20 25 30 35 40 45 50 VCC(V) Tj=125C Vss=GND Tj=25C D97IN732 Figure 11. Switching frquency vs. R1 and C2 . fsw (KHz) 500 0.8 D97IN784 Tamb=25C 200 100 50 20 2nF 1.2 nF 2.2 nF 3.3n F 4.7n F 5.6n F 10 5 0 20 40 60 80 R1(K) 6/13 L4978 Figure 12. Switching Frequency vs. input voltage.. fsw (KHz) 107.5 105.0 102.5 100.0 88 D97IN735 Figure 15. Efficiency vs output voltage. . [%] 98 96 94 92 fsw=100kHz fsw=200kHz Tj=25C 90 97.5 95.0 92.5 90.0 0 5 10 15 20 25 30 35 40 45 50 VCC(V) 86 84 82 80 Vcc=35V Io=2A 0 5 10 15 Vo [V] 20 25 30 Figure 13. Switching frequency vs. junction temperature. fsw (KHz) D97IN785 Figure 16. Efficiency vs. output current. . [%] 95 Vcc=8V Vcc=12V 90 105 85 Vcc=24V 80 100 75 Vcc=48V 70 95 65 fsw=100kHz Vo=5.1V 90 -50 0 50 100 Tj(C) 60 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Io [A] 2 2.2 Figure 14. Dropout voltage between pin 5 and 4. V (V) 0.7 0.6 Tj=125C D98IN836 Figure 17. Efficiency vs. output current. . [%] 95 90 85 Vcc=8V 0.5 Tj = 25 C 80 75 Vcc=12V 0.4 Vcc=24V 0.3 0.2 0.1 0.0 Tj=-25C 70 65 60 Vo=3.36V fsw=100kHz Vcc=48V 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 IO(A) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Io [A] 2 2.2 7/13 L4978 Figure 18. Efficiency vs. output current. . (%) 90 85 80 VCC=48V Io=1.5A D97IN740 Figure 21. Power dissipation vs. Vcc. . Pdiss [mW] 1000 VCC=8V VCC=12V VCC=24V 600 Io=1A Vo=5.1V fsw=100kHz 800 Io=2A 75 70 65 60 fsw=200KHz VO=5.1V 400 Io=0.5A 200 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) 0 10 20 30 Vcc [V] 40 50 60 Figure 19. Efficiency vs. output current. . (%) 90 85 80 75 VCC=8V VCC=12V VCC=24V D97IN741 Figure 22. Device Power dissipation vs. Vo . Pdiss [mW] 1400 Vcc=35V fsw=100kHz Io=2A 1200 1000 Io=1.5A 800 600 Io=1A 70 65 60 VCC=48V fsw=200KHz VO=3.36V 400 Io=0.5A 200 55 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A) 0 0 10 20 Vo [V] 30 Figure 20. Efficiency vs. Vcc. . n [%] 90 Vo=5.1V fsw=100kHz Figure 23. Pulse by pulse limiting current vs. junction temperature.. Ilim (A) 2.9 2.8 2.7 2.6 2.5 fsw=100KHz VCC=35V D97IN747 85 Vo=5.1V fsw=200kHz Vo=3.36V fsw=100kHz 80 Vo=3.36V fsw=200kHz 75 Io=2A 2.4 70 0 10 20 30 Vcc [V] 40 50 60 2.3 -50 -25 0 25 50 75 100 125 Tj(C) 8/13 L4978 Figure 24. Load transient. . Figure 27. Soft start capacitor selection Vs inductor and Vccmax. L (H) D97IN746 fsw=200KHz 56nF 300 47nF 200 33nF 22nF 100 0 15 20 25 30 35 40 45 50 VCCmax(V) Figure 25. Line transient. . VCC (V) 30 20 D97IN786 Figure 28. Open loop frequency and phase of error amplifier . GAIN (dB) 50 GAIN D97IN787 Phase 0 10 1 IO = 1A fsw = 100KHz 0 45 90 Phase VO (mV) 100 0 -50 -100 -150 2 135 -100 1ms/DIV -200 10 102 103 104 105 106 107 108 f(Hz) Figure 26. Soft start capacitor selection Vs inductor and Vccmax. L (H) fsw=100KHz D97IN745 680nF 470nF 400 330nF 300 200 220nF 100 100nF 0 15 20 25 30 35 40 45 50 VCCmax(V) 9/13 L4978 3 Package Informations Figure 29. DIP-8 Mechanical Data & Package Dimensions mm DIM. MIN. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.51 1.15 0.356 0.204 1.65 0.55 0.304 10.92 9.75 0.313 0.100 0.300 0.300 0.260 0.200 0.150 0.060 TYP. 3.32 0.020 0.045 0.014 0.008 0.065 0.022 0.012 0.430 0.384 MAX. MIN. TYP. 0.131 MAX. inch OUTLINE AND MECHANICAL DATA DIP-8 10/13 L4978 Figure 30. SO16 Wide Mechanical Data & Package Dimensions mm DIM. MIN. A A1 B C D (1) E e H h L k ddd 10.0 0.25 0.40 2.35 0.10 0.33 0.23 10.10 7.40 1.27 10.65 0.75 1.27 0.394 0.010 0.016 TYP. MAX. 2.65 0.30 0.51 0.32 10.50 7.60 MIN. 0.093 0.004 0.013 0.009 0.398 0.291 0.050 0.419 0.030 0.050 TYP. MAX. 0.104 0.012 0.200 0.013 0.413 0.299 inch 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 L4978 Table 7. Revision History Date October 2001 May 2005 Revision 8 9 First Issue Modified D1 on the Fig. 4. Description of Changes 12/13 L4978 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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