LT3431 LINER [Linear Technology], LT3431 Datasheet
LT3431
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LT3431 Summary of contents
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... A shutdown pin reduces supply current and the de- vice can be externally synchronized from 580kHz to 700kHz with logic level inputs. The LT3431 is available in a thermally enhanced 16-pin TSSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. MMSD914TI ...
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... SYNC Voltage ........................................................... 7V SHDN Voltage ........................................................... 6V BIAS Pin Voltage .................................................... 30V FB Pin Voltage/Current .................................. 3.5V/2mA Operating Junction Temperature Range LT3431EFE (Notes 8, 10) ................. – 125 C LT3431IFE (Notes 8, 10) ................. – 125 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ELECTRICAL CHARACTERISTICS The ...
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... C to 125 C junction temperature. Specifications over the – 125 C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3431IFE is guaranteed over the full – 125 C operating junction temperature range. Note 9: See Typical Performance Graph of Peak Switch Current Limit vs Junction Temperature ...
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... LT3431 W U TYPICAL PERFOR A CE CHARACTERISTICS Switch Peak Current Limit TYPICAL 4 GUARANTEED MINIMUM 100 DUTY CYCLE (%) 3431 G01 Lockout and Shutdown Thresholds 2.4 LOCKOUT 2.0 1.6 1.2 0.8 START-UP 0.4 SHUTDOWN 0 –50 – 100 JUNCTION TEMPERATURE ( C) 3431 G04 Error Amplifier Transconductance ...
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... SWITCH CURRENT (A) 3431 G14 Switch Peak Current Limit 6.00 5.50 5.00 4.50 4.00 3.50 3.00 2.50 –50 – 100 125 JUNCTION TEMPERATURE ( C) 3431 G16 LT3431 BOOST Pin Current SWITCH CURRENT (A) 3431 G12 Switch Minimum ON Time vs Temperature 600 500 400 ...
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... LT3431 CTIO S GND (Pins 16): 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 ...
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... Most of the circuitry of the LT3431 operates from an internal 2.9V bias line. The bias regulator normally draws power from the regulator input pin, but if the BIAS pin is connected to an external voltage equal to or higher than 3V, bias power will be drawn from the external source (typically the regulated output voltage) ...
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... U U APPLICATIO S I FOR ATIO FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT3431 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 ...
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... Lower values are chosen to reduce physical size of the inductor. Higher values allow more output current because they reduce peak current seen by the LT3431 switch, which has a 3A limit. Higher values also reduce output ripple voltage. When choosing an inductor you will need to consider output ripple voltage, maximum load current, peak induc- tor current and fault current in the inductor ...
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... If maximum load current is 1A, for instance inductor may not survive a continuous 4A overload condition. Dead shorts will actually be more gentle on the inductor because the LT3431 has frequency and current limit foldback. Peak inductor and switch current can be significantly higher than output current, especially with smaller induc- tors and lighter loads, so don’ ...
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... Maximum Output Load Current Maximum load current for a buck converter is limited by the maximum switch current rating (I for the LT3431 is 3A. Unlike most current mode convert- ers, the LT3431 maximum switch current limit does not W U fall off at high duty cycles. Most current mode converters suffer a drop off of peak switch current for duty cycles above 50% ...
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... LP-P The LT3431 is a current mode controller. It uses the V node voltage as an input to a current comparator which turns off the output switch on a cycle-by-cycle basis as peak current is reached. The internal clamp on the V node, nominally 2V, then acts as an output switch peak current limit ...
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... This lower oscillator frequency during short- circuit conditions can then maintain control with the effective minimum on time. Even with frequency foldback, however, the LT3431 will not survive a permanent output short at the absolute maximum voltage rating of V this is defined solely by internal semiconductor junction breakdown effects ...
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... The rise and fall times of these pulses are very fast. The input capacitor is required to reduce the voltage ripple this causes at the input of LT3431 and force the switching current into a tight local loop, thereby minimiz- ing EMI. The RMS ripple current can be calculated from: ...
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... SHUTDOWN FUNCTION AND UNDERVOLTAGE LOCKOUT Figure 4 shows how to add undervoltage lockout (UVLO) to the LT3431. Typically, UVLO is used in situations where the input supply is current limited , or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops ...
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... OUT LT3431 + 2.38V IN – 5.5 A SHDN + – 0.4V GND Figure 4. Undervoltage Lockout 25k suggested for Input voltage at which switching stops as input IN voltage descends to trip level V = Hysteresis in input voltage level Example: output voltage is 5V, switching is to stop if input voltage drops below 12V and should not restart unless input rises back to 13 ...
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... When operating at higher currents and input volt- ages, with poor layout, this spike can generate voltages across the LT3431 that may exceed its absolute maximum rating. A ground plane should always be used under the switcher circuitry to prevent interplane coupling and over- all noise ...
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... Board layout also has a significant effect on thermal resistance. Pins and 16, GND, are a continuous copper plate that runs under the LT3431 die. This is an exposed pad and is the best thermal path for heat out of the package. Soldering the exposed pad to the copper ground plane under the device will reduce die temperature and increase the power capability of the LT3431 ...
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... IN losses. In general, the maximum and minimum V should be checked with maximum typical load current for calculation of the LT3431 die temperature 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 ...
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... The absolute maximum input supply voltage for the LT3431 is specified at 60V. This is based on internal semiconduc- tor junction breakdown effects. The practical maximum input supply voltage for the LT3431 may be less than 60V due to internal power dissipation or switch minimum on time considerations. For the extreme case of an output short-circuit fault to ground, see the section Short-Circuit Considerations ...
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... If LT3431 thermal calculations show power dissipation is not suitable for the given application, the LT3430 is a recommended alternative since it is identical to the LT3431 but runs cooler at 200kHz. Switch minimum on time is the other factor that may limit the maximum operational input voltage for the LT3431 if pulse-skipping behavior is not allowed ...
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... In systems with a primary and backup supply, for ex- 90 ample, a battery powered device with a wall adapter input, 60 the output of the LT3431 can be held up by the backup 30 supply with the LT3431 input disconnected. In this condi- 0 tion, the SW pin will source current into the V ...
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... F 15.4k 10V lation versus its own load current when plotted for three separate load currents on the 5V output. The efficiency of R2 4.99k C the dual polarity output converter circuit shown in Figure SS R3 15nF 2k 14a is given in Figure 14d. 3431 F13 L1: CDRH104R-220M LT3431 sn3431 3431fs 23 ...
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... V LOAD CURRENT (mA) OUT1 3431F14b Figure 14b. V (–5V) Maximum OUT2 Allowable Load Current vs V OUT1 (5V) Load Current MMSD914T1 C2 0. BOOST IN SW SHDN V LT3431EFE OUT1 SYNC BIAS 15.4k 6.3V F 0805 B R3 X5R GND V C 4.99k CER 1.5k F 220pF ...
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... Minimum inductor discontinuous mode: L † MIN D2 L1* Minimum inductor continuous mode: 3 MIN 36. 100 F 16V TANT R2 4.12k For a 12V to –12V converter using the LT3431 with peak OUTPUT** –12V, 0.5A switch current of 3A and a catch diode of 0.52V: 3431 F15 I CONT LT3431 ...
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... LT3431 U U APPLICATIO S I FOR ATIO For a load current of 0.5A, this says that discontinuous mode can be used and the minimum inductor needed is found from MIN 500 10 3 • practice, the inductor should be increased by about 30% over the calculated minimum to handle losses and variations in value ...
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... BSC 0 – 8 0.65 0.45 – 0.75 (.0256) BSC 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3431 4.90 – 5.10* (.193 – .201) 3.58 (.141) 16 1514 2.94 6.40 (.116) BSC ...
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... LT3431 RELATED PARTS PART NUMBER DESCRIPTION LT1074/LT1074HV 4. 100kHz, High Efficiency OUT Step-Down DC/DC Converter LT1076/LT1076HV 1. 100kHz, High Efficiency OUT Step-Down DC/DC Converter LT1616 25V, 500mA (I ), 1.4MHz, High Efficiency OUT Step-Down DC/DC Converter LT1676 60V, 440mA (I ), 100kHz, High Efficiency OUT Step-Down DC/DC Converter LTC1701/LTC1701B 700mA (I ), 1MHz, High Efficiency ...