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LT3493_3.6v-36v转5V芯片手册

2013-05-06 20页 pdf 644KB 20阅读

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LT3493_3.6v-36v转5V芯片手册 LT3493 1 3493fb TYPICAL APPLICATION FEATURES APPLICATIONS DESCRIPTION 1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN n Automotive Battery Regulation n Industrial Control Supplies n Wall Transformer Regulation n Distributed Supply Regulati...
LT3493_3.6v-36v转5V芯片手册
LT3493 1 3493fb TYPICAL APPLICATION FEATURES APPLICATIONS DESCRIPTION 1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN n Automotive Battery Regulation n Industrial Control Supplies n Wall Transformer Regulation n Distributed Supply Regulation n Battery-Powered Equipment L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 3.3V Step-Down Converter Effi ciency n Wide Input Range: 3.6V to 36V Operating, 40V Maximum n 1.2A Output Current n Fixed Frequency Operation: 750kHz n Output Adjustable Down to 780mV n Short-Circuit Robust n Uses Tiny Capacitors and Inductors n Soft-Start n Internally Compensated n Low Shutdown Current: <2μA n Low VCESAT Switch: 330mV at 1A n Thermally Enhanced, Low Profi le DFN Package The LT®3493 is a current mode PWM step-down DC/DC converter with an internal 1.75A power switch. The wide operating input range of 3.6V to 36V (40V maximum) makes the LT3493 ideal for regulating power from a wide variety of sources, including unregulated wall transform- ers, 24V industrial supplies and automotive batteries. Its high operating frequency allows the use of tiny, low cost inductors and ceramic capacitors, resulting in low, predictable output ripple. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. The low current (<2μA) shutdown mode provides output disconnect, enabling easy power management in battery-powered systems. VIN 4.2V TO 36V ON OFF 0.1μF 10μH 32.4k 10μF 3493 TA01a 22pF 1μF 10k VOUT 3.3V 1.2A, VIN > 12V 0.95A, VIN > 5V VIN BOOST GND FB SHDN SW LT3493 LOAD CURRENT (A) EF FI CI EN CY (% ) 70 80 3493 TA01b 60 50 0.4 0.8 1.20.20 0.6 1.0 90 65 75 55 85 VIN = 12V VOUT = 3.3V L = 10μH Administrator 高亮 Administrator 打字机 输入范围:3.6~36V Administrator 高亮 Administrator 打字机 输入范围:3.6V~36V 输出电流:1.2A 固定操作频率:750KHz 输出可调到780mV 有短路保护 ··· Administrator 打字机 Administrator 高亮 Administrator 打字机 Administrator 高亮 Administrator 高亮 Administrator 打字机 较高的操作频率允许了微型低功耗的电感和瓷片电容。这样使得输出的波纹有明显改善。 Administrator 打字机 Administrator 高亮 Administrator 打字机 cycle-by-cycle current limiting 周期性即时电流限制 LT3493 2 3493fb PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS (Note 1) TOP VIEW SHDN VIN SW FB GND BOOST DCB PACKAGE 6-LEAD (2mm s 3mm) PLASTIC DFN 4 57 6 3 2 1 TJMAX = 125°C, θJA = 64°C/W EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 12V, VBOOST = 17V, unless otherwise noted. (Note 2) ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3493EDCB#PBF LT3493EDCB#TRPBF LCGG 6-Lead (2mm × 3mm) Plastic DFN –40°C to 85°C LT3493IDCB#PBF LT3493IDCB#TRPBF LCGH 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3493EDCB LT3493EDCB#TR LCGG 6-Lead (2mm × 3mm) Plastic DFN –40°C to 85°C LT3493IDCB LT3493IDCB#TR LCGH 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/ Input Voltage (VIN) ....................................................40V BOOST Pin Voltage ..................................................50V BOOST Pin Above SW Pin .........................................25V SHDN Pin ..................................................................40V FB Voltage ...................................................................6V Operating Temperature Range (Note 2) LT3493E .............................................. –40°C to 85°C LT3493I ............................................. –40°C to 125°C Maximum Junction Temperature .......................... 125°C Storage Temperature Range ................... –65°C to 150°C PARAMETER CONDITIONS MIN TYP MAX UNITS VIN Operating Range 3.6 36 V Undervoltage Lockout 3.1 3.4 3.6 V Feedback Voltage l 765 780 795 mV FB Pin Bias Current VFB = Measured VREF + 10mV (Note 4) l 50 150 nA Quiescent Current Not Switching 1.9 2.5 mA Quiescent Current in Shutdown VSHDN = 0V 0.01 2 μA Reference Line Regulation VIN = 5V to 36V 0.007 %/V Switching Frequency VFB = 0.7V VFB = 0V 685 750 36 815 kHz kHz Maximum Duty Cycle TA = 25°C l 88 91 95 95 % % Administrator 高亮 Administrator 高亮 Administrator 高亮 Administrator 打字机 欠压锁定 LT3493 3 3493fb Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3493E is guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3493I specifi cations are guaranteed over the –40°C to 125°C temperature range. PARAMETER CONDITIONS MIN TYP MAX UNITS Switch Current Limit (Note 3) 1.4 1.75 2.2 A Switch VCESAT ISW = 1A 330 mV Switch Leakage Current 2 μA Minimum Boost Voltage Above Switch ISW = 1A 1.85 2.2 V BOOST Pin Current ISW = 1A 30 50 mA SHDN Input Voltage High 2.3 V SHDN Input Voltage Low 0.3 V SHDN Bias Current VSHDN = 2.3V (Note 5) VSHDN = 0V 6 0.01 15 0.1 μA μA ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 12V, VBOOST = 17V, unless otherwise noted. (Note 2) Note 3: Current limit guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycle. Note 4: Current fl ows out of pin. Note 5: Current fl ows into pin. TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted. Effi ciency (VOUT = 5V, L = 10μH) LOAD CURRENT (A) 0 50 EF FI CI EN CY (% ) 55 65 70 75 0.8 1.0 95 3493 G01 60 0.2 0.4 0.6 1.2 80 85 90 VIN = 8V VIN = 12V VIN = 24V LOAD CURRENT (A) 0 50 EF FI CI EN CY (% ) 55 65 70 75 0.8 1.0 3493 G02 60 0.2 0.4 0.6 1.2 80 85 90 VIN = 8V VIN = 12V VIN = 24V LOAD CURRENT (A) 0 50 EF FI CI EN CY (% ) 55 65 70 75 0.8 1.0 3493 G03 60 0.2 0.4 0.6 1.2 80 VIN = 5V VIN = 12V Effi ciency (VOUT = 3.3V, L = 10μH) Effi ciency (VOUT = 1.8V, L = 4.7μH) LT3493 4 3493fb Maximum Load Current, VOUT = 5V, L = 8.2μH Maximum Load Current, VOUT = 5V, L = 33μH Maximum Load Current, VOUT = 3.3V, L = 4.7μH Maximum Load Current, VOUT = 3.3V, L = 10μH Switch Voltage Drop Undervoltage Lockout Switching Frequency Frequency Foldback Soft-Start TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted. VIN (V) 8 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 20 28 3493 G04 12 16 24 OU TP UT C UR RE NT (A ) TYPICAL MINIMUM VIN (V) 8 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 20 28 3493 G22 12 16 24 OU TP UT C UR RE NT (A ) TYPICAL MINIMUM VIN (V) 5 1.40 1.50 1.60 25 3493 G05 1.30 1.20 10 15 20 30 1.10 1.00 0.90 OU TP UT C UR RE NT (A ) TYPICAL MINIMUM VIN (V) 5 1.40 1.50 1.60 25 3493 G21 1.30 1.20 10 15 20 30 1.10 1.00 0.90 OU TP UT C UR RE NT (A ) TYPICAL MINIMUM SWITCH CURRENT (A) 0 V C E( SW ) ( m V) 150 450 500 550 0.4 0.8 1.0 3493 G06 50 350 250 100 400 0 300 200 0.2 0.6 1.41.2 1.6 1.8 TA = 25°C TA = 85°C TA = –40°C TEMPERATURE (°C) UV LO (V ) 3.60 3.80 4.00 125 3493 G08 3.40 3.20 3.50 3.70 3.90 3.30 3.10 3.00 –25–50 250 75 100 15050 TEMPERATURE (°C) FR EQ UE NC Y (k Hz ) 720 760 800 125 3493 G09 680 640 700 740 780 660 620 600 –25–50 250 75 100 15050 FEEDBACK VOLTAGE (mV) 0 SW IT CH IN G FR EQ UE NC Y (k Hz ) 400 600 800 3493 G11 200 0 200 400 600100 300 500 700 800 300 500 100 700 SHDN PIN VOLTAGE (V) 0 0 SW IT CH C UR RE NT L IM IT (A ) 0.2 0.6 0.8 1.0 2.0 1.4 0.50 1 1.25 3493 G13 0.4 1.6 1.8 1.2 0.25 0.75 1.50 1.75 2 LT3493 5 3493fb SHDN Pin Current Typical Minimum Input Voltage (VOUT = 5V) Typical Minimum Input Voltage (VOUT = 3.3V) Switch Current Limit Switch Current Limit Operating Waveforms Operating Waveforms, Discontinuous Mode TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted. VSHDN (V) 0 I S H D N (μ A) 30 40 50 16 3493 G14 20 10 25 35 45 15 5 0 42 86 12 14 1810 20 IOUT (mA) 1 5.0 V I N (V ) 6.5 7.0 7.5 10 100 1000 3493 G15 6.0 5.5 TO START TO RUN IOUT (mA) 1 4.3 V I N (V ) 4.5 4.7 4.9 5.1 10 100 1000 3493 G16 4.1 3.9 3.7 3.5 5.3 5.5 TO START TO RUN TEMPERATURE (°C) –50 1.0 SW IT CH C UR RE NT L IM IT (A ) 1.1 1.3 1.4 1.5 2.0 1.7 0 25 100 125 150 3493 G17 1.2 1.8 1.9 1.6 –25 50 75 DUTY CYCLE (%) 0 SW IT CH C UR RE NT L IM IT (A ) 1.2 1.6 2.0 80 3493 G18 0.8 0.4 1.0 1.4 1.8 0.6 0.2 0 20 40 60 100 VSW 5V/DIV IL 0.5A/DIV 0 VOUT 20mV/DIV VIN = 12V VOUT = 3.3V IOUT = 0.5A L = 10μH COUT = 10μF 1μs/DIV 3493 G19 VSW 5V/DIV IL 0.5A/DIV 0 VOUT 20mV/DIV 1μs/DIV 3493 G20VIN = 12V VOUT = 3.3V IOUT = 50mA L = 10μH COUT = 10μF LT3493 6 3493fb BLOCK DIAGRAM PIN FUNCTIONS FB (Pin 1): The LT3493 regulates its feedback pin to 780mV. Connect the feedback resistor divider tap to this pin. Set the output voltage according to VOUT = 0.78V • (1 + R1/R2). A good value for R2 is 10k. GND (Pin 2): Tie the GND pin to a local ground plane below the LT3493 and the circuit components. Return the feedback divider to this pin. BOOST (Pin 3): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. SW (Pin 4): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor. VIN (Pin 5): The VIN pin supplies current to the LT3493’s internal regulator and to the internal power switch. This pin must be locally bypassed. SHDN (Pin 6): The SHDN pin is used to put the LT3493 in shutdown mode. Tie to ground to shut down the LT3493. Tie to 2.3V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. SHDN also provides a soft-start function; see the Applications Infor- mation section. Exposed Pad (Pin 7): The Exposed Pad must be soldered to the PCB and electrically connected to ground. Use a large ground plane and thermal vias to optimize thermal performance. 1 3 R DRIVER Q1 S OSC SLOPE COMP FREQUENCY FOLDBACK INT REG AND UVLO VC gm 780mV 3493 BD 2 5 6 Q Q 3 4 BOOST SW FB R2 R1 VOUT L1 D2 C3 C1D1 VIN C2 VIN ON OFF GND C4 R3 SHDN Administrator 高亮 Administrator 高亮 Administrator 高亮 Administrator 高亮 Administrator 打字机 SHDN模式提供了软启动的功能。 Administrator 高亮 Administrator 高亮 Administrator 打字机 保护二极管 LT3493 7 3493fb OPERATION (Refer to Block Diagram) The LT3493 is a constant frequency, current mode step- down regulator. A 750kHz oscillator enables an RS fl ip-fl op, turning on the internal 1.75A power switch Q1. An amplifi er and comparator monitor the current fl owing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC. An error amplifi er measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node. If the error amplifi er’s output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp (not shown) on the VC node provides current limit. The VC node is also clamped to the voltage on the SHDN pin; soft-start is implemented by generating a voltage ramp at the SHDN pin using an external resistor and capacitor. An internal regulator provides power to the control circuitry. This regulator includes an undervoltage lockout to prevent switching when VIN is less than ~3.4V. The SHDN pin is used to place the LT3493 in shutdown, disconnecting the output and reducing the input current to less than 2μA. The switch driver operates from either the input or from the BOOST pin. An external capacitor and diode are used to generate a voltage at the BOOST pin that is higher than the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for effi cient operation. The oscillator reduces the LT3493’s operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the output current during start- up and overload. Administrator 高亮 LT3493 8 3493fb APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resis- tors according to: R1=R2 VOUT 0.78V – 1 � � � � � � R2 should be 20k or less to avoid bias current errors. Reference designators refer to the Block Diagram. An optional phase lead capacitor of 22pF between VOUT and FB reduces light-load output ripple. Input Voltage Range The input voltage range for LT3493 applications depends on the output voltage and on the absolute maximum rat- ings of the VIN and BOOST pins. The minimum input voltage is determined by either the LT3493’s minimum operating voltage of 3.6V, or by its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: DC= VOUT + VD VIN – VSW + VD where VD is the forward voltage drop of the catch diode (~0.4V) and VSW is the voltage drop of the internal switch (~0.4V at maximum load). This leads to a minimum input voltage of: VIN(MIN) = VOUT + VD DCMAX – VD + VSW with DCMAX = 0.91 (0.88 over temperature). The maximum input voltage is determined by the absolute maximum ratings of the VIN and BOOST pins. For con- tinuous mode operation, the maximum input voltage is determined by the minimum duty cycle DCMIN = 0.10: VIN(MAX) = VOUT + VD DCMIN – VD + VSW Note that this is a restriction on the operating input voltage for continuous mode operation; the circuit will tolerate transient inputs up to the absolute maximum ratings of the VIN and BOOST pins. The input voltage should be limited to the VIN operating range (36V) during overload conditions (short-circuit or start-up). Minimum On Time The part will still regulate the output at input voltages that exceed VIN(MAX) (up to 40V), however, the output voltage ripple increases as the input voltage is increased. Figure 1 illustrates switching waveforms in continuous mode for a 3V output application near VIN(MAX) = 33V. As the input voltage is increased, the part is required to switch for shorter periods of time. Delays associated with turning off the power switch dictate the minimum on time of the part. The minimum on time for the LT3493 is ~120ns. Figure 2 illustrates the switching waveforms when the input voltage is increased to VIN = 35V. VSW 20V/DIV VOUT 200mV/DIV AC COUPLED COUT = 10μF VOUT = 3V VIN = 30V ILOAD = 0.75A L = 10μH 2μs/DIV 3493 F01 IL 0.5A/DIV VSW 20V/DIV VOUT 200mV/DIV AC COUPLED COUT = 10μF VOUT = 3V VIN = 35V ILOAD = 0.75A L = 10μH 2μs/DIV 3493 F02 IL 0.5A/DIV Figure 1 Figure 2 LT3493 9 3493fb APPLICATIONS INFORMATION Now the required on-time has decreased below the minimum on time of 120ns. Instead of the switch pulse width becoming narrower to accommodate the lower duty cycle requirement, the switch pulse width remains fi xed at 120ns. In Figure 2 the inductor current ramps up to a value exceeding the load current and the output ripple increases to ~200mV. The part then remains off until the output voltage dips below 100% of the programmed value before it begins switching again. Provided that the load can tolerate the increased output voltage ripple and that the components have been properly selected, operation above VIN(MAX) is safe and will not damage the part. Figure 3 illustrates the switching wave- forms when the input voltage is increased to its absolute maximum rating of 40V. As the input voltage increases, the inductor current ramps up quicker, the number of skipped pulses increases and the output voltage ripple increases. For operation above VIN(MAX) the only component requirement is that the com- ponents be adequately rated for operation at the intended voltage levels. The part is robust enough to survive prolonged operation under these conditions as long as the peak inductor current does not exceed 2.2A. Inductor current saturation may further limit performance in this operating regime. Inductor Selection and Maximum Output Current A good fi rst choice for the inductor value is: L = 1.6 (VOUT + VD) where VD is the voltage drop of the catch diode (~0.4V) and L is in μH. With this value there will be no subharmonic oscillation for applications with 50% or greater duty cycle. The inductor’s RMS current rating must be greater than your maximum load current and its saturation current should be about 30% higher. For robust operation in fault conditions, the saturation current should be above 2.2A. To keep effi ciency high, the series resistance (DCR) should be less than 0.1Ω. Table 1 lists several vendors and types that are suitable. Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value provides a higher maximum load current and reduces output voltage ripple at the expense of slower transient response. If your load is lower than 1.2A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physi- cally smaller inductor, or one with a lower DCR resulting in higher effi ciency. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output volt- ages. Low inductance may result in discontinuous mode operation, which is okay, but further reduces maximum load current. For details of the maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. Catch Diode Depending on load current, a 1A to 2A Schottky diode is recommended for the catch diode, D1. The diode must have a reverse voltage rating equal to or greater than the maximum input voltage. The ON Semiconductor MBRM140 is a good choice; it is rated for 1A continuous forward current and a maximum reverse voltage of 40V. VSW 20V/DIV VOUT 200mV/DIV AC COUPLED COUT = 10μF VOUT = 3V VIN = 40V ILOAD = 0.75A L = 10μH 2μs/DIV 3493 F03 IL 0.5A/DIV Figure 3 LT3493 10 3493fb APPLICATIONS INFORMATION Input Capacitor Bypass the input of the LT3493 circuit with a 1μF or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and ap- plied voltage and should not be used. A 1μF ceramic is adequate to bypass the LT3493 and will easily handle the ripple current. However, if the input power source has high impedance, or there is signifi cant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input sup- ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3493 and to force this very high frequency switching current into a tight
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