Final Electrical Specifications LT3433 High Voltage Step-Up/Step-Down DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LT®3433 is a 200kHz fixed-frequency current mode switching regulator that provides both step-up and stepdown regulation using a single inductor. The IC operates over a 4V to 60V input voltage range making it suitable for use in various wide input voltage range applications such as automotive electronics that must withstand both load dump and cold crank conditions. Automatic Step-Up and Step-Down Conversion Uses a Single Inductor Wide 4V to 60V Input Voltage Range VOUT from 3.3V to 20V Dual Internal 500mA Switches 100µA No-Load Quiescent Current Low Current Shutdown ±1% Output Voltage Accuracy 200kHz Operating Frequency Boosted Supply Pin to Saturate High Side Switch Frequency Foldback Protection Current Limit Foldback Protection Current Limit Unaffected by Duty Cycle 16-lead Thermally Enhanced TSSOP Package Internal control circuitry monitors system conditions and converts from single switch buck operation to dual switch bridged operation when required, seamlessly changing between step-down and step-up voltage conversion. Optional Burst Mode® operation reduces no-load quiescent current to 100µA and maintains high efficiencies with light loads. U APPLICATIO S ■ ■ ■ September 2003 Current limit foldback and frequency foldback help prevent inductor current runaway during start-up. Programmable soft-start helps prevent output overshoot at start-up. 12V Automotive Systems Wall Adapter Powered Systems Battery Power Voltage Buffering The LT3433 is available in a 16-lead thermally enhanced TSSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. U TYPICAL APPLICATIO 4V to 60V to 5V DC/DC Converter with Burst Mode Operation VOUT 5V 4V ≤ VIN ≤ 8.5V: 125mA 8.5V ≤ VIN ≤ 60V: 350mA B160A B120A 1N4148 SW_L 0.1µF SW_H PWRGND LT3433 VIN + VOUT 1N4148 2.2µF BURST_EN 1nF100pF VBIAS 0.1µF SHDN VC 68k VFB 100k 0.5% 305k 0.5% SS Efficiency 500 47µF 90 VOUT = 5V MAXIMUM OUTPUT CURRENT (mA) VBST VIN 4V TO 60V Maximum Output Current vs VIN BUCK 80 400 VIN = 13.8V 70 EFFICIENCY (%) L1 100µH CoEv DU1352-101M 300 200 BRIDGED 60 50 VIN = 4V 40 100 30 SGND 0 0.01µF 3433 TA01 0 10 20 30 VIN (V) 40 50 60 3433 TA01c 20 0.1 10 100 1 OUTPUT CURRENT (mA) 1000 3433 TA01b 3433ia Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1 LT3433 U U W W W Input Supply (VIN) .................................... –0.3V to 60V Boosted Supply (VBST) .............. –0.3V to VSW_H + 30V (VBST(MAX) = 80V) Internal Supply (VBIAS) ............................. – 0.3V to 30V SW_H Switch Voltage .................................. – 2V to 60V SW_L Switch Voltage ............................... – 0.3V to 30V Feedback Voltage (VFB) ............................... – 0.3V to 5V Operating Junction Temperature Range (Note 5) LT3433E (Note 6) ............................ – 40°C to 125°C LT3433I ........................................... – 40°C to 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C W (Note 1) U ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION ORDER PART NUMBER TOP VIEW SGND 1 16 SGND VBST 2 15 SW_L SW_H 3 14 PWRGND VIN 4 13 VOUT BURST_EN 5 12 VBIAS VC 6 11 SHDN VFB 7 10 SS SGND 8 9 17 LT3433EFE LT3433IFE FE PART MARKING SGND 3433EFE 3433IFE FE PACKAGE 16-LEAD PLASTIC TSSOP TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W EXPOSED PAD (PIN 17) MUST BE SOLDERED TO SGND Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 13.8V, VFB = 1.25V, VOUT = 5V, VBURST_EN = 0V, VBST – VIN = 5V, unless otherwise noted. SYMBOL PARAMETER VIN Operating Voltage Range VIN(UVLO) Undervoltage Lockout CONDITIONS MIN ● Enable Threshold 3.4 ● Undervoltage Lockout Hysteresis VOUT Operating Voltage Range VBST Operating Voltage Range MAX UNITS 60 V 3.95 V 160 mV ● 3.3 20 V VBST < VSW_H + 20V VBST – VSW_H ● ● 3.3 75 20 V V (Notes 2, 3) VVC < 0.6V VSHDN < 0.4V ● ● ● 580 100 10 940 190 25 µA µA µA 2.6 2.9 V 20 V IVIN Normal Operation Burst Mode Operation Shutdown VBIAS Internal Supply Output Voltage ● Operating Voltage Range ● IVBIAS TYP 4 ● 660 0.1 0.1 4.5 990 µA µA µA mA ISW = 500mA ● 0.8 1.2 Ω Output Supply Switch On-Resistance ISW = 500mA ● 0.6 1 Ω Shutdown Pin Thresholds Disable Enable ● ● 1 V V Normal Operation Burst Mode Operation Shutdown Short-Circuit Current Limit VVC < 0.6V VSHDN < 0.4V RSWH(ON) Boost Supply Switch On-Resistance RSWL(ON) VSHDN 0.4 IVBST/ISW Boost Supply Switch Drive Current High Side Switch On, ISW = 500mA ● 30 50 mA/A IVOUT/ISW Output Supply Switch Drive Current Low Side Switch On, ISW = 500mA ● 30 50 mA/A ILIM Switch Current Limit 0.7 0.9 A Foldback Current Limit ISS Soft-Start Output Current VFB Feedback Reference Voltage ● 0.5 ● 3 5 9 µA 1.224 1.215 1.231 ● 1.238 1.245 V V VFB = 0V 0.35 A 3433ia 2 LT3433 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 13.8V, VFB = 1.25V, VOUT = 5V, VBURST_EN = 0V, VBST – VIN = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS ∆VFB Feedback Reference Line Regulation 5.5V ≤ VIN ≤ 60V IFB VFB Pin Input Bias Current ● 0.002 0.01 %/V ● 35 100 nA gm Error Amplifier Transconductance ● 270 330 umhos AV Error Amplifier Voltage Gain ISW/VVC Control Voltage to Switch Transconductance fO Operating Frequency 200 VFB > 1V 185 170 ● 66 dB 0.55 A/V 200 215 230 kHz kHz Foldback Frequency VFB = 0V tON(MIN) Minimum Switch On Time RL = 35Ω (Note 4) ● 250 450 ns tOFF(MIN) Minimum Switch Off Time RL = 35Ω (Note 4) ● 500 800 ns Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Supply current specification does not include switch drive currents. Actual supply currents will be higher. Note 3: “Normal Operation” supply current specification does not include IBIAS currents. Powering the VBIAS pin externally reduces ICC supply current. Note 4: Minimum times are tested using the high side switch with a 35Ω load to ground. 50 kHz Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 6: The LT3433E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3433I is guaranteed over the full –40°C to 125°C operating junction temperature range. U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum Output Current vs VIN VBIAS Output Voltage vs Temperature VIN Supply Current vs VIN Supply Voltage 620 2.8 500 TA = 25°C BUCK 300 200 BRIDGED 100 0 SEE TYPICAL APPLICATION ON THE FIRST PAGE OF THIS DATA SHEET 0 10 20 30 VIN (V) 40 50 60 3433 G11 590 2.6 IVIN (µA) 400 VBIAS OUTPUT VOLTAGE (V) MAXIMUM OUTPUT CURRENT (mA) VOUT = 5V 560 2.4 530 2.2 –50 500 0 50 TEMPERATURE (°C) 100 125 3433 G01 0 15 30 VIN (V) 45 60 3433 G02 3433ia 3 LT3433 U W TYPICAL PERFOR A CE CHARACTERISTICS Error Amp Reference vs Temperature Soft-Start Current vs Temperature 7.0 Switch Current Limit vs VFB 1.232 700 ERROR AMP REFERENCE (V) ISS (µA) 6.0 5.5 5.0 SWITCH CURRENT LIMIT (mA) TA = 25°C 6.5 1.231 1.230 1.229 4.5 4.0 –50 0 50 TEMPERATURE (°C) 100 1.228 –50 125 500 400 300 0 50 TEMPERATURE (°C) 100 3433 G03 125 0.2 0 0.6 0.4 VFB (V) 1.0 Switch Current Limit vs Temperature Oscillator Frequency vs VFB 210 0.8 3433 G05 3433 G04 Oscillator Frequency vs Temperature 750 200 TA = 25°C 205 200 195 190 –50 0 50 TEMPERATURE (°C) 100 150 CURRENT LIMIT (mA) OSCILLATOR FREQUENCY (kHz) OSCILLATOR FREQUENCY (kHz) 600 100 125 50 0 0.2 0 3433 G06 0.6 0.4 VFB (V) 0.8 725 700 675 650 –50 1.0 0 50 TEMPERATURE (°C) Maximum Output Supply Switch Drive Current vs Output Supply Voltage 70 70 65 65 IVOUT/ISW (mA/A) IBST/ISW (mA/A) 125 3433 G08 3433 G07 Maximum Boost Supply Switch Drive Current vs Boost Supply Voltage 100 60 55 50 60 55 50 45 45 4 5 6 7 8 9 10 VBST – VSW_H (V) 11 12 4 5 6 7 8 9 10 11 12 VOUT (V) 3433 G09 3433 G10 3433ia 4 LT3433 U U U PI FU CTIO S SGND (Pins 1, 8, 9, 16): Low Noise Ground Reference. VBST (Pin 2): Boosted Switch Supply. This “boosted” supply rail is referenced to the SW_H pin. Supply voltage is maintained by a bootstrap capacitor tied from the VBST pin to the SW_H pin. A 1µF capacitor is generally adequate for most applications. The charge on the bootstrap capacitor is refreshed through a diode, typically connected from the converter output (VOUT), during the switch-off period. Minimum off-time operation assures that the boost capacitor is refreshed each switch cycle. The LT3433 supports operational VBST supply voltages up to 75V (absolute maximum) as referenced to ground. SW_H (Pin 3): Boosted Switch Output. This is the current return for the boosted switch and corresponds to the emitter of the switch transistor. The boosted switch shorts the SW_H pin to the VIN supply when enabled. The drive circuitry for this switch is boosted above the VIN supply through the VBST pin, allowing saturation of the switch for maximum efficiency. The “ON” resistance of the boosted switch is 0.8Ω. VIN (Pin 4): Input Power Supply. This pin supplies power to the boosted switch and corresponds to the collector of the switch transistor.This pin also supplies power to most of the IC’s internal circuitry if the VBIAS pin is not driven externally. This supply will be subject to high switching transient currents so this pin requires a high quality bypass capacitor that meets whatever application-specific input ripple current requirements exist. See Applications Information. BURST_EN (Pin 5): Burst Mode Enable Pin. Shorting this pin to SGND enables Burst Mode operation. If Burst Mode operation is not desired, connecting this pin to VBIAS or VOUT will disable the burst function. VC (Pin 6): Error Amplifier Output. The voltage on the VC pin corresponds to the maximum switch current per oscillator cycle. The error amplifier is typically configured as an integrator circuit by connecting an RC network from this pin to ground. This circuit typically creates the dominant pole for the converter regulation feedback loop. Specific integrator characteristics can be configured to optimize transient response. See Applications Information. VFB (Pin 7): Error Amplifier Inverting Input. The noninverting input of the error amplifier is connected to an internal 1.231V reference. The VFB pin is connected to a resistor divider from the converter output. Values for the resistor connected from VOUT to VFB (RFB1) and the resistor connected from VFB to ground (RFB2) can be calculated to program converter output voltage (VOUT) via the following relation: VOUT = 1.231 • (RFB1 + RFB2)/RFB2 The VFB pin input bias current is 35nA, so use of extremely high value feedback resistors could cause a converter output that is slightly higher than expected. Bias current error at the output can be estimated as: ∆VOUT(BIAS) = 35nA • RFB1 The voltage on VFB also controls the LT3433 oscillator frequency through a “frequency-foldback” function. When the VFB pin voltage is below 0.8V, the oscillator runs slower than the 200kHz typical operating frequency. The oscillator frequency slows with reduced voltage on the pin, down to 50kHz when VFB = 0V. The VFB pin voltage also controls switch current limit through a “current-limit foldback” function. At VFB = 0V, the maximum switch current is reduced to half of the normal value. The current limit value increases linearly until VFB reaches 0.6V when the normal maximum switch current level is restored. The frequency and current-limit foldback functions add robustness to short-circuit protection and help prevent inductor current runaway during start-up. SS (Pin 10): Soft Start. Connect a capacitor (CSS) from this pin to ground. The output voltage of the LT3433 error amplifier corresponds to the peak current sense amplifier output detected before resetting the switch output(s). The soft-start circuit forces the error amplifier output to a zero peak current for start-up. A 5µA current is forced from the SS pin onto an external capacitor. As the SS pin voltage ramps up, so does the LT3433 internally sensed peak current limit. This forces the converter output current to ramp from zero until normal output regulation is achieved. This function reduces output overshoot on converter start-up. 3433ia 5 LT3433 U U U PI FU CTIO S The time from VSS = 0V to maximum available current can be calculated given a capacitor CSS as: tSS = (2.7 • 105)CSS or 0.27s/µF SHDN (Pin 11): Shutdown. If the SHDN pin is externally pulled below 0.5V, low current shutdown mode is initiated. During shutdown mode, all internal functions are disabled, and ICC is reduced to 10µA. This pin is intended to receive a digital input, however, there is a small amount of input hysteresis built into the SHDN circuit to help assure glitchfree mode switching. If shutdown is not desired, connect the SHDN pin to VIN. VBIAS (Pin 12): Internal Local Supply. Much of the LT3433 circuitry is powered from this supply, which is internally regulated to 2.5V through an on-board linear regulator. Current drive for this regulator is sourced from the VIN pin. The VBIAS supply is short-circuit protected to 5mA. The VBIAS supply only sources current, so forcing this pin above the regulated voltage allows the use of external power for much of the LT3433 circuitry. When using external drive, this pin should be driven above 3V to assure the internal supply is completely disabled. This pin is typically diodeconnected to the converter output to maximize conversion efficiency. This pin must be bypassed with at least a 0.1µF ceramic capacitor to SGND. VOUT (Pin 13): Converter Output Pin. This pin voltage is compared with the voltage on VIN internally to control operation in single or 2-switch mode. When the ratios of the two voltages are such that a >75% duty cycle is required for regulation, the low side switch is enabled. Drive bias for the low side switch is also derived directly from this pin. PWRGND (Pin 14): High Current Ground Reference. This is the current return for the low side switch and corresponds to the emitter of the low side switch transistor. SW_L (Pin 15): Ground Referenced Switch Output. This pin is the collector of the low side switch transistor. The low side switch shorts the SW_L pin to PWRGND when enabled. The series impedance of the ground-referenced switch is 0.6Ω. 3433ia 6 LT3433 W BLOCK DIAGRA VBIAS 1.25V BURST CONTROL CIRCUITS BIAS 12 BURST_EN 5 VIN 4 SENSE AMPLIFIER VBST 2 COMPARATOR BOOSTED DRIVER SW_H 3 SLOPE COMP OSCILLATOR 200kHz FREQUENCY CONTROL MODE CONTROL SWITCH CONTROL LOGIC SW_L 15 DRIVER GND VFB 14 7 ERROR AMPLIFIER 30% LOAD 1.231V VC + Burst Mode CONTROL SHDN 6 11 SHUTDOWN – 15% LOAD 0.7V SS 10 5µA VOUT SGND 1, 8, 9,16 13 3433 BD VOUT + 3433ia 7 LT3433 U W U U APPLICATIO S I FOR ATIO Overview The LT3433 is a high input voltage range, step-up/stepdown DC/DC converter IC using a 200kHz constant frequency, current mode architecture. Dual internal switches allow the full input voltage to be imposed across the switched inductor, such that both step-up and step-down modes of operation can be realized using the same single inductor topology. The LT3433 has provisions for high efficiency, low load operation for battery-powered applications. Burst Mode operation reduces average quiescent current to 100µA in no load conditions. A low current shutdown mode can also be activated, reducing total quiescent current to 10µA. Much of the LT3433’s internal circuitry is biased from an internal low voltage linear regulator. The output of this regulator is brought out to the VBIAS pin, allowing bypassing of the internal regulator. The associated internal circuitry can be powered directly from the output of the converter, increasing overall converter efficiency. Using externally derived power also eliminates the IC’s power dissipation associated with the internal VIN to VBIAS regulator. Theory of Operation (See Block Diagram) The LT3433 senses converter output voltage via the VFB pin. The difference between the voltage on this pin and an internal 1.231V reference is amplified to generate an error voltage on the VC pin which is, in turn, used as a threshold for the current sense comparator. During normal operation, the LT3433 internal oscillator runs at 200kHz. At the beginning of each oscillator cycle, the switch drive is enabled. The switch drive stays enabled until the sensed switch current exceeds the VC-derived threshold for the current sense comparator and, in turn, disables the switch driver. If the current comparator threshold is not obtained for the entire oscillator cycle, the switch driver is disabled at the end of the cycle for 250ns. This minimum off-time mode of operation assures regeneration of the VBST bootstrapped supply. If the converter input and output voltages are close together, proper operation in normal buck configuration would require high duty cycles. The LT3433 senses this condition as requiring a duty cycle greater than 75%. If such a condition exists, a second switch is enabled during the switch on time, which acts to pull the output side of the inductor to ground. This “bridged” operation allows voltage conversion to continue when VOUT approaches or exceeds VIN. Shutdown The LT3433 incorporates a low current shutdown mode where all IC functions are disabled and the VIN current is reduced to 10µA. Pulling the SHDN pin down to 0.4V or less activates shutdown mode. Burst Mode Operation The LT3433 employs low current Burst Mode functionality to maximize efficiency during no load and low load conditions. Burst Mode function is disabled by shorting the BURST_EN pin to either VBIAS or VOUT. Burst Mode function is enabled by shorting BURST_EN to SGND. When the required switch current, sensed via the VC pin voltage, is below 30% of maximum, the Burst Mode function is employed. When the voltage on VC drops below the 30% load level, that level of sense current is latched into the IC. If the output load requires less than this latched current level, the converter will overdrive the output slightly during each switch cycle. This overdrive condition forces the voltage on the VC pin to continue to drop. When the voltage on VC drops below the 15% load level, switching is disabled, and the LT3433 shuts down most of its internal circuitry, reducing quiescent current to 100µA. When the voltage on the VC pin climbs back to 20% load level, the IC returns to normal operation and switching resumes. Antislope Compensation Most current mode switching controllers use slope compensation to prevent current mode instability. The LT3433 is no exception. A slope compensation circuit imposes an artificial ramp on the sensed current to increase the rising slope as duty cycle increases. Unfortunately, this additional ramp corrupts the sensed current value, reducing the achievable current limit value by the same amount as the added ramp represents. As such, current limit is typically reduced as duty cycles increase. 3433ia 8 LT3433 U W U U APPLICATIO S I FOR ATIO The LT3433 contains circuitry to eliminate the current limit reduction associated with slope-compensation, or antislope compensation. As the slope compensation ramp is added to the sensed current, a similar ramp is added to the current limit threshold reference. The end result is that current limit is not compromised so the LT3433 can provide full power regardless of required duty cycle. Mode Switching The LT3433 senses operational duty cycle by directly monitoring VIN and VOUT. Voltage drops associated with pass and catch diodes are estimated internally such that mode switching occurs when the duty cycle required for continuous buck operation is greater than 75%. If such a condition exists, a second switch is enabled during the switch on time, changing operation to a dual switch bridged configuration. Because the voltage available across the switched inductor is greater in bridged mode, duty cycle will decrease. The output current in bridged mode is not continuous, so switch currents are considerably higher than while operating in buck mode. In order to maximize available output power, continuous operation and low ripple currents are recommended. Switch currents will increase by a factor of 1/(1 – DC) during bridged mode, so this mode of operation is typically the gating item for converter drive capability. switch current will be reduced by this required drive current. IDRIVE = DC • 2 • ISW(MAX) • ISWDRIVE(MAX) Using 50mA/A for the required drive current for each switch yields the portion of switch current used to drive the switches is: ISW(DRIVE) = DC • 2 • ISW(MAX) • 0.05/(1 – DC) Removing drive currents from the available maximum switch current yields: ISW(MAX)' = ISW(MAX) • [1 – DC • 2 • ISW(MAX) • 0.05/(1 – DC)] where ISW(MAX)' is maximum switch current available to the load during bridged operation. The maximum load current can then be calculated as: ILOAD(MAX) = ISW(MAX)' • (1 – DC) which reduces to: ILOAD(MAX) = [0.5A – (∆IL/2)] • (1 – 1.1 • DC) Design Equations VIN SW_H IOUT(MAX) = ISW(MAX) • (1 –␣ DC) LT3433 = [0.5A – (∆IL / 2)] • (1 – DC) L SW_L VOUT where ∆IL is the ripple current in the inductor. It is also important to note that IOUT cannot be considered equivalent to ILOAD during bridged operation. Most of the converter’s switch drive power is derived from the generated output supply, so IOUT must also accommodate this current requirement. During single-switch buck operational conditions, switch drive current is negligible in terms of output current; however, during bridged operation, these currents can become significant. These output derived switch drive currents will increase the current loading on VIN by the same 1/(1 – DC) factor as the switch currents. As maximum switch current is referenced to that coming from the VIN supply, the available maximum 3433 AI01 Constants: VSWH = voltage drop across boosted switch VSWL = voltage drop across grounded switch VF = forward drop of external Schottky diodes f0 = operating frequency Duty Cycle (continuous operation): DCBUCK = (VOUT + 2VF)/(VIN – VSWH + VF) DCBRIDGED = (VOUT + 2VF)/(VOUT + VIN + 2VF – VSWH – VSWL) 3433ia 9 LT3433 U W U U APPLICATIO S I FOR ATIO Ripple current: ∆IL(P −P) = (VOUT + 2VF ) • (1− DC ) L • fO Inductor Selection The primary criterion for inductor value selection in LT3433 applications is the ripple current created in that inductor. Design considerations for ripple current are the amount of output ripple and the ability of the internal slope compensation waveform to prevent current mode instability. The LT3433 maximizes available dynamic range using a slope compensation generator that generates a continuously increasing slope as duty cycle increases. The slope compensation waveform is calibrated at 80% duty cycle to compensate for ripple currents up to 12.5% of IMAX, or ~ 60mA. Ripple current can be calculated as: ∆IL(P −P) = (VOUT + 2VF ) • (1− DC ) L • fO Discontinuous operation occurs when the ripple current in the inductor is greater than twice the load current (ILOAD) in buck mode, or greater than ILOAD/(1 – DC) during bridged mode. Current mode instability is not a concern during discontinuous operation so inductor values smaller than LMIN can be used. If such a small inductor is used, however, it must be assured that the converter never enters continuous operation at duty cycles greater than 50% to prevent current mode instability. Design Example VIN(MIN) = 4V, VOUT = 5V, L = 150µH Using VF = 0.75V yields: DC = (VOUT + 2VF)/(VOUT + VIN + 2VF – VSWH – VSWL) = (5V + 1.5V)/(4V + 5V + 1.5V – 0.6V – 0.5V) = 0.69 ∆IL = (VOUT + 2VF) • (1 – DC) • (L •␣ f0)–1 = (5V + 1.5V) • (1 –␣ 0.69) • (150µH • 200kHz)–1 = 67mA ILOAD(MAX) = ISW(MAX) • (1 – 1.1 • DC) This relation can be used to determine minimum inductance sizes for various values of VOUT using the DC = 80% calibration: = [0.5A – (1/2 • 0.07)](1 – 1.1 • 0.69) = 0.112A LMIN = (VOUT + 1.5V) • (1 – 0.8) 60mA • 200kHz) VOUT LMIN 4V 92µH 5V 108µH 9V 175µH 12V 225µH 3433ia 10 LT3433 U TYPICAL APPLICATIO Burst Only Low Noise 5V Maintenance Supply DS1 B160A DS2 B160A L1 33µH D1 1N4148 VBST C1 0.1µF VIN 4V TO 60V + SW_L SW_H PWRGND LT3433 VIN VOUT C7 2.2µF C6 100pF R2 510k 5% BURST_EN VBIAS VC SHDN VFB R1 2.2M 5% D2 1N4148 C2 0.1µF SS IN SGND OUT LT1761-5 SHDN GND BYP C4 0.01µF C5 2.2µF VOUT 5V 10mA C3 10µF 3433 TA03 U PACKAGE DESCRIPTIO FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BB 4.90 – 5.10* (.193 – .201) 3.58 (.141) 3.58 (.141) 16 1514 13 12 1110 6.60 ±0.10 9 2.94 (.116) 4.50 ±0.10 SEE NOTE 4 2.94 6.40 (.116) BSC 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 1.10 (.0433) MAX 4.30 – 4.50* (.169 – .177) 0° – 8° 0.09 – 0.20 (.0036 – .0079) 0.45 – 0.75 (.018 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE 0.65 (.0256) BSC 0.195 – 0.30 (.0077 – .0118) 0.05 – 0.15 (.002 – .006) FE16 (BB) TSSOP 0203 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 3433ia 11 LT3433 U TYPICAL APPLICATIO 4V-60V to 5V at 100mA DC/DC Converter Burst Disabled DS1 B160A DS2 B160A L1 100µH C6 47µF D2 1N4148 C1 0.1µF VIN 4V TO 60V + VBST SW_L SW_H PWRGND LT3433 VOUT VIN C7 2.2µF C5 1nF C4 100pF R1 68k R2 100k 0.5% R3 305k 0.5% VOUT 5V 100mA BURST_EN VBIAS VC SHDN D1 1N4148 C2 0.1µF SS VFB SGND C3 0.01µF 3433 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1076/LT1076HV 1.6A (IOUT), 100kHz High Efficiency Step-Down DC/DC Converters VIN: 7.3V to 45V/64V, VOUT(MIN): 2.21V, IQ: 8.5mA, ISD: 10µA, DD5/DD7, TO220-5/TO220-7 LT1676 60V, 440mA (IOUT), 100kHz High Efficiency Step-Down DC/DC Converter VIN: 7.4V to 60V, VOUT(MIN): 1.24V, IQ: 3.2mA, ISD: 2.5µA, SO-8 LT1765 25V, 2.75A (IOUT), 1.25MHz High Efficiency Step-Down DC/DC Converter VIN: 3V to 25V, VOUT(MIN): 1.20V, IQ: 1mA, ISD: 15µA, SO-8, TSSOP16E LT1766/LT1956 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters VIN: 5.5V to 60V, VOUT(MIN): 1.20V, IQ: 2.5mA, ISD: 25µA, TSSOP16/TSSOP16E LT1767 25V, 1.2A (IOUT), 1.25MHz High Efficiency Step-Down DC/DC Converter VIN: 3V to 25V, VOUT(MIN): 1.20V, IQ: 1mA, ISD: 6µA, MS8/MS8E LT1776 40V, 550mA (IOUT), 200kHz High Efficiency Step-Down DC/DC Converter VIN: 7.4V to 40V, VOUT(MIN): 1.24V, IQ: 3.2mA, ISD: 30µA, N8, SO-8 LT1976 60V, 1.2A (IOUT), 200kHz High Efficiency Micropower (IQ < 100µA) Step-Down DC/DC Converter VIN: 3.3V to 60V, VOUT(MIN): 1.20V, IQ: 100µA, ISD: <1µA, TSSOP16E LT3010 80V, 50mA Low Noise Linear Regulator VIN: 1.5V to 80V, VOUT(MIN): 1.28V, IQ: 30µA, ISD: <1µA, MS8E LTC3412/LTC3414 2.5A (IOUT), 4MHz Synchronous Step-Down DC/DC Converters VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60µA, ISD: <1µA, TSSOP16E LTC3414 4A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter VIN: 2.3V to 5.5V, VOUT(MIN): 0.8V, IQ: 64µA, ISD: <1µA, TSSOP20E LTC3727/LTC3727-1 36V, 500kHz High Efficiency Step-Down DC/DC Controllers VIN: 4V to 36V, VOUT(MIN): 0.8V, IQ: 670µA, ISD: 20µA, QFN32, SSOP28 LT3430/LT3431 60V, 2.75A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters VIN: 5.5V to 60V, VOUT(MIN): 1.20V, IQ: 2.5mA, ISD: 30µA, TSSOP16E LTC3440 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter with 95% Efficiency VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25µA, ISD: <1µA, MS10 3433ia 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT/TP 0903 1K REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2003