lt1776 Linear Technology Corporation, lt1776 Datasheet
lt1776
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lt1776 Summary of contents
Page 1
... The internal control circuitry is normally powered via the V CC from the V action of the LT1776 switch circuitry is also load depen- dent. At medium to high loads, the output switch circuitry maintains fast rise time for good efficiency. At light loads, rise time is deliberately reduced to avoid pulse skipping behavior ...
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... Pin Voltage ....................................................... 30V CC FB Pin Voltage ........................................................... 3V Operating Junction Temperature Range LT1776C ................................................ 125 C LT1776I ............................................ – 125 C Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are T ...
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... See Applications section for more information. Note 6: Internal oscillator is guaranteed to sync up to 400kHz. However, thermal constraints and/or controllability issues may place a lower limit on switching frequency in actual usage. See Applications section for more information. LT1776 = MIN TYP MAX ...
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... DUTY CYCLE (%) 1776 G03 SHDN Pin Lockout Thresholds vs Temperature 1.30 1.28 UPPER THRESHOLD 1.26 LOWER THRESHOLD 1.24 1.22 1.20 –50 – 100 125 TEMPERATURE ( C) LT1776 G06 Switch Minimum On-Time vs Temperature 600 V = 40V 500 FB = 400 300 200 100 0 50 100 125 –50 –25 ...
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... THRESHOLD 1.0 0.8 –50 – 100 125 TEMPERATURE ( C) LT1776 G10 PIN FUNCTIONS SHDN (Pin 1): When pulled below the shutdown mode threshold, nominally 0.30V, this pin turns off the regulator and reduces V input current to a few tens of microam- IN peres (shutdown mode). ...
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... LT1776 PIN FUNCTIONS 10% and 90% duty cycle. The sync function is internally disabled if the FB pin voltage is low enough to cause oscillator slowdown. If unused, this pin should be grounded. FB (Pin 7): This is the inverting input to the feedback amplifier. The noninverting input of this amplifier is inter- nally tied to the 1.24V reference. This pin also slows down ...
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... BOOST SWOFF U OPERATIO The LT1776 is a current mode switching regulator IC that has been optimized for high efficiency operation in high input voltage, low output voltage buck topologies. The Block Diagram shows an overall view of the system. Several of the blocks are straightforward and similar to those found in traditional designs, including: Internal Bias Regulator, Oscillator and Feedback Amplifier ...
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... In a typical application, proper inductance value is dictated by matching the discontinuous/continuous crossover point with the LT1776 internal low-to-high dV/dt threshold. This is the best compromise between maintaining control with light loads while maintaining good efficiency with heavy loads ...
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... OUT User selection of an appropriate output capacitor is rela- tively easy, as this capacitor sees only the AC ripple current in the inductor. As the LT1776 is designed for buck or step-down applications, output voltage will nearly always be compatible with tantalum type capacitors, which are generally available in ratings up to 35V or so. These tantalum types offer good volumetric efficiency and many are available with specified ESR performance ...
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... ON time. Cycle skipping and/or odd/ even cycle behavior will result although correct output voltage is usually maintained. Minimum Load Considerations As discussed previously, a lightly loaded LT1776 with V pin control voltage below the boost threshold will operate in low dV/dt mode. This affords greater controllability at light loads, as minimum t ...
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... Burst Mode operation behavior (see Typical Applications and Figure 8). Maximum Load/Short-Circuit Considerations The LT1776 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 this 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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... VCC OUT (This assumes that the V pin is connected Power loss internal to the LT1776 related to actual output current is composed of both DC and AC switching losses. These can be roughly estimated as follows: DC switching losses are dominated by output switch “ON voltage”, i.e • I • DC ...
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... LT1776 Figure 3. High Speed Current Switching Paths Additionally possible for the LT1776 to cause EMI problems by “coupling to itself”. Specifically, this can occur if the V pin is allowed to capacitively couple uncontrolled manner to the part’s high impedance nodes, i.e., SHDN, SYNC, V and FB ...
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... Resistor R5 is chosen to have approximately 200 A through it at the nominal SHDN pin lockout threshold of 1.25V. The somewhat arbitrary value of 200 A was SHDN LT1776 39 F MBRS1100 100pF 63V SYNC 2200pF X7R R3 GND 22k ...
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... Behavior is as follows: Normal operation is observed at the nominal input voltage of 40V. As the input voltage is decreased to roughly 32V, switching action will stop, V will drop to zero, and the LT1776 will draw its V quiescent currents from the V supply much lower IN input voltage, typically 14V the voltage on ...
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... Intentional hysteresis is set by the R5/ R6 divider. As the output voltage falls below the regulation range, the LT1776 is turned on. The output voltage rises, and as it climbs above the regulation range, the LT1776 is turned off. Efficiency is maximized, as the LT1776 is only powered up while it is providing heavy output current. ...
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... OUT LTC1440 6 22k REF 5 HYST – V GND 10V 40V 30V 20V 100 1000 LOAD CURRENT (mA) 1776 F07b (b) LT1776 V OUT + 39k 5% R2 10k 5% R3 323k 1% R4 100k 1% 1776 F07a 17 ...
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... The circuit, as shown, accommodates an input voltage range of 10V to 30V. The accompanying graphs display efficiency for input voltages of 12V and 24V. The upper input voltage limit of 30V is determined not by the LT1776, but by the LT1121-5 regulator (U3). (A regulated 5V is required by the LT1620.) This regulator was chosen for its ...
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... TYP 0.014 – 0.019 (0.355 – 0.483) LT1776 0.130 0.005 (3.302 0.127) 0.125 0.020 (3.175) MIN (0.508) MIN 0.018 0.003 (0 ...
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... Low Noise Buck Regulator Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com Wide V Range, High Efficiency Battery Charger SHDN LT1776 100 SYNC 2200pF C3 MBRS1100 GND 100pF R3 22k ...