L4972AD

L4972A 2A SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 Features 2A OUTPUT CURRENT 5.1V TO 40V OUTPUT VOLTAGE RANGE 0 TO 90% DUTY CYCLE RANGE INTERNAL FEED-FORWARD LINE REG. INTERNAL CURRENT LIMITING PRECISE 5.1V ± 2% ON CHIP REFERENCE RESET AND POWER FAIL FUNCTIONS INPUT/OUTPUT SYNC PIN UNDER VOLTAGE LOCK OUT WITH HYSTERETIC TURN-ON PWM LATCH FOR SINGLE PULSE PER PERIOD VERY HIGH EFFICIENCY SWITCHING FREQUENCY UP TO 200KHz THERMAL SHUTDOWN CONTINUOUS MODE OPERATION Description The L4972A is a stepdown monolithic power switching regulator delivering 2A at a voltage variable from 5.1 to 40V. Realized with BCD mixed technology, the device Figure 1. Packages PowerDIP20 (16+2+2) SO20 Table 1. Order Codes Part Number Package L4972A DIP20 (16+2+20) L4972AD SO20 L4972AD013TR SO20 in Tape & Reel uses a DMOS output transistor to obtain very high efficiency and very fast switching times. Features of the L4972 include reset and power fail for microprocessors, feed forward line regulation, soft start, limiting current and thermal protection. The device is mounted in a Powerdip 16 + 2 + 2 and SO20 large plastic packages and requires few external components. Efficient operation at switching frequencies up to 200KHz allows reduction in the size and cost of external filter component. Figure 2. Block Diagram May 2005 Rev. 3 1/22 L4972A Table 2. Pin Description N° Pin 1 BOOTSTRAP A Cboot capacitor connected between this terminal and the output allows to drive properly the internal D-MOS transistor. Function 2 RESET DELAY A Cd capacitor connected between this terminal and ground determines the reset signal delay time. 3 RESET OUT Open Collector Reset/power Failand the output voltages are safe. Signal Output. This output is high when the supply 4 RESET INPUT Input of Power Fail Circuit. The threshold is 5.1V. It may be connected via a divider to the input for power fail function. It must be connected to the pin 14 an external 30KΩ resistor when power fail signal not required. 5, 6 15, 16 GROUND 7 FREQUENCY COMPENSATION 8 SOFT START 9 FEEDBACK INPUT The Feedback Terminal of the Regulation Loop. The output is connected directly to this terminal for 5.1V operation; It is connected via a divider for higher voltages. 10 SYNC INPUT Multiple L4972A’s are synchronized by connecting pin 10 inputs together or via an external syncr. pulse. Common Ground Terminal A series RC network connected between this terminal and ground determines the regulation loop gain characteristics. Soft Start Time Constant. A capacitor is connected between the sterminal and ground to define the soft start time constant. 11 SUPPLY VOLTAGE 12, 19 N.C. Unregulated Input Voltage. Not Connected. 13 Vref 5.1V Vref Device Reference Voltage. 14 Vstart Internal Start-up Circuit to Drive the Power Stage. 17 OSCILLATOR Rosc. External resistor connected to ground determines the constant charging current of Cosc. 18 OSCILLATOR Cosc. External capacitor connected to ground determines (with Rosc) the switching frequency. 20 OUTPUT Regulator Output. Figure 3. Pin Connection (Top view) BOOTSTRAP 1 20 OUTPUT RESET DELAY 2 19 N.C. RESET OUT 3 18 C OSC P. FAIL INPUT 4 17 R OSC GND 5 16 GND GND 6 15 GND FREQ. COMP. 7 14 Vstart SOFT START 8 13 Vref FEEDBACK IN. 9 12 N.C. 10 11 Vi SYNC INPUT DIP20 2/22 L4972A Table 3. Absolute Maximum Ratings Symbol Parameter Value Unit V11 Input Voltage 55 V V11 Input Operating Voltage 50 V V20 Output DC Voltage Output Peak Voltage at t = 0.1µs f = 200kHz -1 -5 V V I20 Maximum Output Current VI Boostrap Voltage Boostrap Operating Voltage 65 V11 + 15 V V V4, V8 V3 Internally Limited Input Voltage at Pins 4, 12 12 V Reset Output Voltage 50 V Reset Output Sink Current 50 mA Input Voltage at Pin 2, 7, 9, 10 7 V I2 Reset Delay Sink Current 30 mA I7 Error Amplifier Output Sink Current 1 A I8 Soft Start Sink Current 30 mA Total Power Dissipation at TPINS ≤ 90°C at Tamb = 70°C (No copper area on PCB) 5 / 3.75(*) 1.3/1 (*) W W Junction and Storage Temperature -40 to 150 °C I3 V2, V7, V9, V10 Ptot TJ, Tstg (*) SO-20 Table 4. Thermal Data Symbol 3 PowerDIP SO20 Unit Rth j-pins Thermal Resistance Junction-Pins Parameter max, 12 16 °C/W Rth j-amb Thermal Resistance Junction-ambient max, 60 80 °C/W Circuit Operation The L4972A is a 2A monolithic stepdown switching regulator working in continuous mode realized in the new BCD Technology. This technology allows the integration of isolated vertical DMOS power transistors plus mixed CMOS/Bipolar transistors. The device can deliver 2A at an output voltage adjustable from 5.1V to 40V and contains diagnostic and control functions that make it particularly suitable for microprocessor based systems. 3.1 BLOCK DIAGRAM The block diagram shows the DMOS power transistors and the PWM control loop. Integrated functions include a reference voltage trimmed to 5.1V ± 2%, soft start, undervoltage lockout, oscillator with feedforward control, pulse by pulse current limit, thermal shutdown and finally the reset and power fail circuit. The reset and power fail circuit provides an output signal for a microprocessor indicating the status of the system. Device turn on is around 11V with a typical 1V hysterysis, this threshold porvides a correct voltage for the driving stage of the DMOS gate and the hysterysis prevents instabilities. An external bootstrap capacitor charge to 12V by an internal voltage reference is needed to provide correct gate drive to the power DMOS. The driving circuit is able to source and sink peak currents of around 0.5A to the gate of the DMOS transistor. A typical switching time of the current in the DMOS transistor is 50ns. Due to the fast commutation switching frequencies up to 200kHz are possible. The PWM control loop consists of a sawtooth oscillator, error amplifier, comparator, latch and the output 3/22 L4972A stage. An error signal is produced by comparing the output voltage with the precise 5.1V ± 2% on chip reference. This error signal is then compared with the sawtooth oscillator in order to generate frixed frequency pulse width modulated drive for the output stage. A PWM latch is included to eliminate multiple pulsing within a period even in noisy environments. The gain and stability of the loop can be adjusted by an external RC network connected to the output of the error amplifier. A voltage feedforward control has been added to the oscillator, this maintains superior line regulation over a wide input voltage range. Closing the loop directly gives an output vol-tage of 5.1V, higher voltages are obtained by inserting a voltage divider. At turn on, output overcurrents are prevented by the soft start function (fig. 5). The error amplifier is initially clamped by an external capacitor, Css, and allowed to rise linearly under the charge of an internal constant current source. Output overload protection is provided by a current limit circuit. The load current is sensed by a internal metal resistor connected to a comparator. When the load current exceeds a preset threshold, the output of the comparator sets a flip flop which turns off the power DMOS. The next clock pulse, from an internal 40kHz oscillator, will reset the flip flop and the power DMOS will again conduct. This current protection method, ensures a constant current output when the system is overloaded or short circuited and limits the switching frequency, in this condition, to 40kHz. The Reset and Power fail diagram (fig. 7), generates an output signal when the supply voltage exceeds a threshold programmed by an external voltage divider. The reset signal, is generated with a delay time programmed by a external capacitor on the delay pin. When the supply voltage falls below the threshold or the output voltage goes below 5V, the reset output goes low immediately. The reset output is an open drain. Fig. 7A shows the case when the supply voltage is higher than the threshold, but the output voltage is not yet 5V. Fig. 7B shows the case when the output is 5.1V, but the supply voltage is not yet higher than the fixed threshold. The thermal protection disables circuit operation when the junction temperature reaches about 150°C and has a hysterysis to prevent unstable conditions. Figure 4. Feedforward Waveform. Figure 5. Soft Start Function. 4/22 L4972A Figure 6. Limiting Current Function. Figure 7. Reset and Power Fail Functions A B 5/22 L4972A 4 Electrical Characteristcs Table 5. Electrical Characteristcs Refer to the test circuit, TJ = 25°C, Vi = 35V, R4 = 30KΩ, C9 = 2.7nF, fSW = 100KHz typ, unless otherwise specified. Symbol Parameter Test Condition Min. Typ. Max. Unit Fig. 50 V 8 5.1 5.2 V 8 DYNAMIC CHARACTERISTICS Vi Input Volt. Range (pin 11) Vo = Vref to 40V Io = 2A (**) 15 Vo Output Voltage Vi =15V to 50V Io= 1A; Vo = Vref 5 ∆Vo Line Regulation Vi =15V to 50V Io = 0.5A; Vo= Vref 12 30 mV ∆Vo Load Regulation Vo = Vref Io= 0.5A to 2A 7 20 mV Vd Dropout Voltage between Pin 11 and 20 Io = 2A 0.25 0.4 V I20L Max Limiting Current Vi = 15V to 50V Vo= Vref to 40V 2.5 2.8 3.5 A Efficiency (*) Io = 2A, f = 100KHz Vo = Vref Vo = 12V 75 85 90 % % Supply Voltage Ripple Rejection Vi = 2VRMS; Io= 1A f = 100Hz; Vo= Vref 56 60 dB 8 Switching Frequency 90 100 110 KHz 8 6 % 8 % 8 KHz 8 η SVR f ∆f/∆Vi Voltage Stability of Switching Frequency Vi = 15V to 45V 2 ∆f/Tj Temperature Stability of Switching Frequency Tj = 0 to 125°C 1 fmax Maximum Operating Switching Frequency Vo= Vref R4 = 15KΩ Io = 2A C9= 2.2nF 200 (*) Only for DIP version (**) Pulse testing with a low duty cycle Vref SECTION (pin 13) V13 Reference Voltage ∆V13 Line Regulation ∆V13 Load Regulation ∆V13 /∆T Average Temperature Coefficient Reference Voltage I13 short Short Circuit Current Limit 5 Vi = 15V to 50V 5.1 5.2 V 10 10 25 mV 10 40 I13 = 0 to 1mA 20 mV 10 Tj = 0°C to 125°C 0.4 mV/°C 10 V13 = 0 70 mA 10 V 10 VSTART SECTION (pin 15) V14 Reference Voltage ∆V14 Line Regulation Vi = 15 to 50V 0.6 1.4 V 10 ∆V14 Load Regulation I14 = 0 to 1mA 50 200 mV 10 Short Circuit Current Limit V15 = 0V 80 mA 10 12 V 12 I14 short 11.4 12 12.6 DC CHARACTERISTICS V11on Turn-on Threshold 10 V11 Hyst Turn-off Hysteresys 11 V 12 I11Q Quiescent Current V8 = 0; S1 = D 13 19 mA 12 I11OQ Operating Supply Current V8 = 0; S1 = B; S2 = B 16 23 mA 12 6/22 1 L4972A Table 5. Electrical Characteristcs (continued) Refer to the test circuit, TJ = 25°C, Vi = 35V, R4 = 30KΩ, C9 = 2.7nF, fSW = 100KHz typ, unless otherwise specified. Symbol I20L Parameter Out Leak Current Test Condition Min. Typ. Vi = 55V; S3 = A; V8= 0 Max. Unit Fig. 2 mA 12 150 µA 13 1 0.7 V V 13 13 V 14 SOFT START (pin 8) I8 Soft Start Source Current V8 = 3V; V9= 0V V8 Output Saturation Voltage I8 = 20mA; V11= 10V I8= 200µA; V11= 10V 80 115 ERROR AMPLIFIER V7H High Level Out Voltage I7 = 100µA; S1 = C; V9 = 4.7V 6 V7L Low Level Out Voltage I7 = 100µA; S1 = C; V9= 5.3V I7H Source Output Current V7 = 1V; V7 = 4.7V 100 150 1.2 100 150 Sink Output Current V7 = 6V; V9 = 5.3V I9 Input Bias Current S1 = B; RS = 10KΩ GV DC Open Loop Gain S1 = A; RS= 10Ω 60 60 -I7L SVR Supply Voltage Rejection 15 < Vi < 50V VOS Input Offset Voltage RS= 50Ω S1 = A 0.4 3 80 V 14 µA 14 µA 14 µA 14 dB 14 dB 14 mV 14 1.5 V 12 2.5 5.5 V V 12 12 2 10 RAMP GENERATOR (pin 18) V18 Ramp Valley S1 = B; S2 = B V18 Ramp Peak S1 = B; S2 = B Vi = 15V Vi = 45V 1.2 I18 Min. Ramp Current S1 = A; I17= 100µA I18 Max. Ramp Current S1 = A; I17= 1mA 2.4 270 300 2.7 µA 12 mA 12 SYNC FUNCTION (pin 10) V10 Low Input Voltage Vi = 15V to 50V; V8 = 0; S1 = B; S2 = B; S4 = B –0.3 0.9 V 12 V10 High Input voltage V8 = 0; S1 = B; S2 = B; S4 = B 2.5 5.5 V 12 I10L Sync Input Current with Low Input Voltage V10= V18= 0.9V; S4 = B; S1 = B; S2 = B 0.4 mA 12 I10H Input Current with High Input Voltage V10= 2.5V 1.5 mA 12 V10 Output Amplitude V – tW Output Pulse Width Vthr = 2.5V 4 5 0.3 0.5 0.8 µs – RESET AND POWER FAIL FUNCTIONS V9R Rising Thereshold Voltage (pin 9) Vi = 15 to 50V V4 = 5.3V Vref -130 Vref -100 Vref -80 V mV 15 V9F Falling Thereshold Voltage (pin 9) Vi = 15 to 50V V4 = 5.3V 4.77 Vref -200 Vref -160 V mV 15 V2H Delay High Threshold Volt. Vi = 15 to 50V V4 = 5.3V; V9 = V13 4.95 5.1 5.25 V 15 V2L Delay Low Threshold Volt. Vi = 15 to 50V;V4 = 4.7V; V9 = V13 1 1.1 1.2 V 15 I2SO Delay Source Current V4 = 5.3V; V2 = 3V 30 60 80 µA 15 I2SI Delay Source Sink Current V4 = 4.7V; V2 = 3V 10 mA 15 V3S Output Saturation Voltage I3 = 15mA; S1 = B V4 = 4.7V 0.4 V 15 Output Leak Current V3 = 50V; S1 = A 100 µA 15 I3 7/22 L4972A Table 5. Electrical Characteristcs (continued) Refer to the test circuit, TJ = 25°C, Vi = 35V, R4 = 30KΩ, C9 = 2.7nF, fSW = 100KHz typ, unless otherwise specified. Symbol Parameter V4R Rising Threshold Voltage V4H Hysteresis I4 Test Condition V9 = V13 Input Bias Current Min. Typ. Max. Unit 4.95 5.1 5.25 V 15 0.4 0.5 0.6 V 15 1 3 µA 15 Figure 8. TYPICAL PERFORMANCES (using evaluation board) : n = 83% (Vi = 35V ; Vo = VREF ; Io = 2A ; fsw = 100KHz) Vo RIPPLE = 30mV (at 1A) Line regulation = 12mV (Vi = 15 to 50V) Load regulation = 7mV (Io = 0.5 to 2A) for component values Refer to the fig. 8 (Part list). Figure 9. Component Layout of fig. 8. Evaluation Board Available (only for DIP version) 8/22 Fig. L4972A PART LIST R1 = 30KΩ R2 = 10KΩ R3 = 15KΩ R4 = 30KΩ R5 = 22Ω R6 = 4.7KΩ R7 = see table 6 R8 = OPTION R9 = 4.7KΩ * C1 = C2 = 1000mF 63V EYF (ROE) C3 = C4 = C5 = C6 = 2,2µF 50V C7 = 390pF Film C8 = 22nF MKT 1837 (ERO) C9 = 2.7nF KP 1830 (ERO) C10 = 0.33µF Film C11 = 1nF ** C12 = C13 = C14 = 100µF 40V EKR (ROE) C15 = 1µF Film D1 = STPS5L60 L1 = 150µH core 58310 MAGNETICS 45 TURNS 0.91mm (AWG 19) COGEMA 949181 * 2 capacitors in parallel to increase input RMS current capability. * * 3 capacitors in parallel to reduce total output ESR. Table 6. V0 R9 R7 12V 4.7kΩ 6.2kΩ 15V 4.7kΩ 9.1kΩ 18V 4.7kΩ 12Ω 24V 4.7kΩ 18Ω Note: In the Test and Application Circuit for L4972D are not mounted C2, C14 and R8. Table 7. Suggested Boostrap Capacitors Operating Frequency Boostrap Cap.c10 f = 20KHz ≥680nF f = 50KHz ≥470nF f = 100KHz ≥330nF f = 200KHz ≥220nF f = 500KHz ≥100nF 9/22 L4972A Figure 10. P.C. Board and Component Layout of the Circuit of Fig. 8. Figure 11. DC Test Circuits Figure 12. 10/22 L4972A Figure 13. Figure 14. Figure 15. Figure 16. Quiescent Drain Current vs. Supply Voltage (0% duty cycle - see fig. 12). Figure 17. Quiescent Drain Current vs. Junction Temperature (0% duty cycle). 11/22 L4972A Figure 18. Quiescent Drain Current vs. Duty Cycle. Figure 21. Reference Voltage (pin 14) vs. Vi (see fig. 11). Figure 19. Reference Voltage (pin 13) vs. Vi (see fig. 11). Figure 22. Reference Voltage (pin 14) vs. Junction Temperature (see fig. 11). Figure 20. Reference Voltage (pin 13) vs. Junction Temperature (see fig. 11). Figure 23. : Ref. Voltage 5.1V (pin 13) Supply Voltage Ripple Rejection vs. Frequency 12/22 L4972A Figure 24. Switching Frequency vs. Input Voltage (see fig. 8). Figure 27. Maximum Duty Cycle vs. Frequency. Figure 25. Switching Frequency vs. Junction Temperature (see fig. 8). Figure 28. Supply Voltage Ripple Rejection vs. Frequency (see fig. 8). Figure 26. Switching Frequency vs. R4 (see fig.8). Figure 29. Efficiency vs. Output Voltage. 13/22 L4972A Figure 30. Line Transient Response (see fig. 8). Figure 33. .Dropout Voltage between Pin 11 and Pin 20 vs. Junction Temperature. Figure 31. Line Transient Response (see fig. 8). Figure 34. Power Dissipation (device only) vs. Input Voltage. Figure 32. Dropout Voltage between Pin 11 and Pin 20 vs. Current at Pin 20. Figure 35. Power Dissipation (device only) vs. Input Voltage. 14/22 L4972A Figure 36. Power Dissipation (device only) vs. Output Voltage. Figure 39. Power Dissipation (device only) vs. Output Current Figure 37. Power Dissipation (device only) vs. Output Voltage Figure 40. Efficiency vs. Output Current. Figure 38. Power Dissipation (device only) vs. Output Current Figure 41. Test PCB Thermal Characteristic. 15/22 L4972A Figure 42. Rth j-amb vs. Area on Board Heatsink (DIP 16+2+2) Figure 45. Maximum Allowable Power Dissipation vs. Ambient Temperature (SO20) Figure 43. Rth j-amb vs. Area on Board Heatsink (SO20) Figure 46. Open Loop Frequency and Phase of Error Amplifier (see fig. 14). Figure 44. Maximum Allowable Power Dissipation vs. Tamb (Powerdip) 16/22 L4972A Figure 47. 2A – 5.1V Low Cost Application Circuit. Figure 48. A 5.1V/12V Multiple Supply. Note the Synchronization between the L4972A and L4970A. Figure 49. L4972A’s Sync. Example. 17/22 L4972A Figure 50. 1A/24V Multiple Supply. Note the synchronization between the L4972A and L4962 18/22 L4972A 5 Package Information Figure 51. PowerDIP20 Mechanical Data & Package Dimensions mm DIM. MIN. a1 0.51 B 0.85 b b1 TYP. inch MAX. MIN. TYP. MAX. 0.020 1.40 0.033 0.50 0.38 0.055 0.020 0.50 D 0.015 0.020 24.80 0.976 E 8.80 0.346 e 2.54 0.100 e3 22.86 0.900 F 7.10 0.280 I 5.10 0.201 L OUTLINE AND MECHANICAL DATA 3.30 0.130 Powerdip 20 Z 1.27 0.050 19/22 L4972A Figure 52. SO20 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) 12.60 13.00 0.496 0.512 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. SO20 0016022 D 20/22 L4972A 6 Revision History Table 8. Revision History Date Revision Description of Changes June 2000 2 First Issue May 2005 3 Modified look & feel layout. Changed the name of D1 in the Part list to page 9/22. 21/22 L4972A 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. All other names are the property of their respective owners © 2005 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com 22/22