LT3430/LT3430-1 High Voltage, 3A, 200kHz/100kHz Step-Down Switching Regulators DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Wide Input Range: 5.5V to 60V 3A Peak Switch Current over All Duty Cycles Constant Switching Frequency: 200kHz (LT3430) 100kHz (LT3430-1) 0.1Ω Switch Resistance Current Mode Effective Supply Current: 2.5mA Shutdown Current: 30µA 1.
LT3430/LT3430-1 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) TOP VIEW Input Voltage (VIN) .................................................. 60V BOOST Pin Above SW (Note 11) .............................. 35V BOOST Pin Voltage ................................................. 68V SYNC Voltage ............................................................. 7V ⎯S⎯H⎯D⎯N Voltage ............................................................ 6V BIAS Pin Voltage .....................................
LT3430/LT3430-1 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VIN = 15V, VC = 1.5V, ⎯S⎯H⎯D⎯N = 1V, BOOST = Open Circuit, SW = Open Circuit, unless otherwise noted. PARAMETER CONDITIONS MIN TYP 96 94 98 ● ● 184 172 200 200 216 228 kHz kHz ● 88 85 100 100 115 120 kHz kHz 0.05 0.
LT3430/LT3430-1 TYPICAL PERFORMANCE CHARACTERISTICS Switch Peak Current Limit ⎯S⎯H⎯D⎯N Pin Bias Current FB Pin Voltage and Current 1.234 6 250 2.0 TJ = 25°C 4 GUARANTEED MINIMUM 3 1.5 1.224 VOLTAGE 1.219 1.0 CURRENT 1.
LT3430/LT3430-1 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Input Voltage with 5V Output Switching Frequency 230 7.5 (LT3430) BOOST Pin Current 90 TA = 25°C TA = 25°C 80 210 200 190 6.5 MINIMUM INPUT VOLTAGE TO START 6.0 MINIMUM INPUT VOLTAGE TO RUN 5.5 180 –25 0 50 25 75 100 5.0 125 0 JUNCTION TEMPERATURE (°C) 70 60 50 40 30 20 10 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.
LT3430/LT3430-1 PIN FUNCTIONS GND (Pins 1, 8, 9, 16, 17): The GND pin connections act as the reference for the regulated output, so load regulation will suffer if the “ground” end of the load is not at the same voltage as the GND pins of the IC. This condition will occur when load current or other currents flow through metal paths between the GND pins and the load ground. Keep the paths between the GND pins and the load ground short and use a ground plane when possible.
LT3430/LT3430-1 BLOCK DIAGRAM it much easier to frequency compensate the feedback loop and also gives much quicker transient response. The LT3430/LT3430-1 are constant frequency, current mode buck converters. This means that there is an internal clock and two feedback loops that control the duty cycle of the power switch. In addition to the normal error amplifier, there is a current sense amplifier that monitors switch current on a cycle-by-cycle basis.
LT3430/LT3430-1 APPLICATIONS INFORMATION FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT3430/LT3430-1 is used to set output voltage and provide several overload protection features. The first part of this section deals with selecting resistors to set output voltage and the second part talks about foldback frequency and current limiting created by the FB pin. Please read both parts before committing to a final design.
LT3430/LT3430-1 APPLICATIONS INFORMATION LT3430 VSW TO FREQUENCY SHIFTING 1.4V – OUTPUT 5V Q1 ERROR AMPLIFIER + L1 R1 1.2V R4 2k R3 1k FB + C1 BUFFER Q2 R2 TO SYNC CIRCUIT VC GND 3430 F02 Figure 2. Frequency and Current Limit Foldback tion should be used if resistors are increased beyond the suggested values and short-circuit conditions occur with high input voltage. High frequency pickup will increase and the protection accorded by frequency and current foldback will decrease.
LT3430/LT3430-1 APPLICATIONS INFORMATION inductor value to achieve a desirable output ripple voltage level. If output ripple voltage is of less importance, the subsequent suggestions in Peak Inductor and Fault Current and EMI will additionally help in the selection of the inductor value. Peak-to-peak output ripple voltage is the sum of a triwave (created by peak-to-peak ripple current (ILP-P) times ESR) and a square wave (created by parasitic inductance (ESL) and ripple current slew rate).
LT3430/LT3430-1 APPLICATIONS INFORMATION Peak switch and inductor current can be significantly higher than output current, especially with smaller inductors and lighter loads, so don’t omit this step. Powdered iron cores are forgiving because they saturate softly, whereas ferrite cores saturate abruptly. Other core materials fall somewhere in between.
LT3430/LT3430-1 APPLICATIONS INFORMATION Reduced Inductor Value and Discontinuous Mode If the smallest inductor value is of most importance to a converter design, in order to reduce inductor size/cost, discontinuous mode may yield the smallest inductor solution. The maximum output load current in discontinuous mode, however, must be calculated and is defined later in this section. Discontinuous mode is entered when the output load current is less than one-half of the inductor ripple current (ILP-P).
LT3430/LT3430-1 APPLICATIONS INFORMATION where: f = switching frequency tON = switch minimum on time VF = diode forward voltage VIN = Input voltage I • R = inductor I • R voltage drop If this condition is not observed, the current will not be limited at IPK, but will cycle-by-cycle ratchet up to some higher value. Using the nominal LT3430/LT3430-1 clock frequencies of 200KHz/100kHz, a VIN of 40V and a (VF + I • R) of say 0.
LT3430/LT3430-1 APPLICATIONS INFORMATION frequency gain of the error amplifier, including the gain at the switching frequency. If the gain of the error amplifier is high enough at the switching frequency, output ripple voltage (although smaller for a ceramic output capacitor) may still affect the proper operation of the regulator. A filter capacitor CF in parallel with the RC/CC network is suggested to control possible ripple at the VC pin.
LT3430/LT3430-1 APPLICATIONS INFORMATION poor RFI behavior and if the overshoot is severe enough, damage the IC itself. The suggested catch diode (D1) is an International Rectifier 30BQ060 Schottky. It is rated at 3A average forward current and 60V reverse voltage. Typical forward voltage is 0.52V at 3A. The diode conducts current only during switch off time. Peak reverse voltage is equal to regulator input voltage.
LT3430/LT3430-1 APPLICATIONS INFORMATION RFB L1 LT3430/LTC3430-1 2.38V IN INPUT OUTPUT VSW + STANDBY RHI – 5.5µA + SHDN C1 + TOTAL SHUTDOWN RLO C2 0.4V – GND 3430 F04 Figure 4. Undervoltage Lockout R HI = [ RLO VIN − 2.38( ∆V/VOUT + 1) + ∆V ( 2.38 − RLO (5 .
LT3430/LT3430-1 APPLICATIONS INFORMATION LAYOUT CONSIDERATIONS ing this path will also reduce the parasitic trace inductance of approximately 25nH/inch. At switch off, this parasitic inductance produces a flyback spike across the LT3430/ LT3430-1 switch. When operating at higher currents and input voltages, with poor layout, this spike can generate voltages across the LT3430/LT3430-1 that may exceed its absolute maximum rating.
LT3430/LT3430-1 APPLICATIONS INFORMATION The VC and FB components should be kept as far away as possible from the switch and boost nodes. The LT3430/ LT3430-1 pinout has been designed to aid in this. The ground for these components should be separated from the switch current path. Failure to do so will result in poor stability or subharmonic like oscillation. Board layout also has a significant effect on thermal resistance.
LT3430/LT3430-1 APPLICATIONS INFORMATION THERMAL CALCULATIONS Power dissipation in the LT3430/LT3430-1 chip comes from four sources: switch DC loss, switch AC loss, boost circuit current, and input quiescent current. The following formulas show how to calculate each of these losses. These formulas assume continuous mode operation, so they should not be used for calculating efficiency at light load currents.
LT3430/LT3430-1 APPLICATIONS INFORMATION lower VIN may generate greater losses due to switch DC losses. In general, the maximum and minimum VIN levels should be checked with maximum typical load current for calculation of the LT3430/LT3430-1 die temperature. If a more accurate die temperature is required, a measurement of the SYNC pin resistance (to GND) can be used. The SYNC pin resistance can be measured by forcing a voltage no greater than 0.
LT3430/LT3430-1 APPLICATIONS INFORMATION ings = 0.233W • 45°C/W = 11°C. The 7V zener should be sized for excess of 0.233W operaton. The tolerances of the zener should be considered to ensure minimum VC2 exceeds 3.3V + VDROOP. Input Voltage vs Operating Frequency Considerations The absolute maximum input supply voltage for the LT3430/ LT3430-1 is specified at 60V. This is based solely on internal semiconductor junction breakdown effects.
LT3430/LT3430-1 APPLICATIONS INFORMATION stability. This ESR, however, contributes significantly to the ripple voltage at the output (see Output Ripple Voltage in the Applications Information section). It is possible to reduce capacitor size and output ripple voltage by replacing the tantalum output capacitor with a ceramic output capacitor because of its very low ESR. The zero provided by the tantalum output capacitor must now be reinserted back into the loop.
LT3430/LT3430-1 APPLICATIONS INFORMATION LT3430/LT3430-1 will consume their quiescent operating current of 1.5mA. The VIN pin will also source current to any other components connected to the input line. If this load is greater than 10mA or the input could be shorted to ground, a series Schottky diode must be added, as shown in Figure 12. With these safeguards, the output can be held at voltages up to the VIN absolute maximum rating. output.
LT3430/LT3430-1 APPLICATIONS INFORMATION DUAL OUTPUT SEPIC CONVERTER POSITIVE-TO-NEGATIVE CONVERTER The circuit in Figure 14 generates both positive and negative 5V outputs with a single piece of magnetics. The two inductors shown are actually just two windings on a standard Coiltronics inductor. The topology for the 5V output is a standard buck converter. The – 5V topology would be a simple flyback winding coupled to the buck converter if C4 were not present.
LT3430/LT3430-1 APPLICATIONS INFORMATION D2† MMSD914TI INPUT 5.5V TO 44V C2 0.68µF BOOST L1* 10µH VSW VIN R1 36.5k LT3430 GND C3 4.7µF 100V CER Minimum inductor continuous mode: (VIN )(VOUT ) LMIN = ⎡ ⎛ (V + VF )⎞ ⎤ 2(f)(VIN + VOUT )⎢IP – IOUT ⎜ 1 + OUT ⎟⎥ ⎝ ⎠⎦ VIN ⎣ D4 7V VC FB CC CF D1 30BQ060 RC D3 30BQ015 + R2 4.12k C1 100µF 16V TANT OUTPUT** –12V, 0.5A * INCREASE L1 FOR HIGHER CURRENT APPLICATIONS.
LT3430/LT3430-1 APPLICATIONS INFORMATION value equal to the peak-to-peak triangular waveform of the inductor. The low output ripple design in Figure 15 places the input capacitor between VIN and the regulated negative output. This placement of the input capacitor significantly reduces the size required for the output capacitor (versus placing the input capacitor between VIN and ground). ESR of the chosen capacitor (see Output Ripple Voltage in Applications Information).
LT3430/LT3430-1 PACKAGE DESCRIPTION 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 2.94 6.40 (.116) (.252) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
LT3430/LT3430-1 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1074/LT1074HV 4.4A (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converters VIN: 7.3V to 45V/64V, VOUT(MIN): 2.21V, IQ: 8.5mA, ISD: 10µA DD-5/7, TO220-5/7 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 DD-5/7, TO220-5/7 LT1676 60V, 440mA (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converter VIN: 7.4V to 60V, VOUT(MIN): 1.24V, IQ: 3.
