LT1576-5 Linear Technology, LT1576-5 Datasheet

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... LTC and LT are registered trademarks of Linear Technology Corporation 1N914 L1 OUTPUT** SW 5V, 1.25A 15.8k 1N5818 100 F, 10V C 4.99k SOLID TANTALUM 1576 TA01 LT1576/LT1576-5 Switching Regulator U Efficiency vs Load Current 100 OUT V = 10V 0.50 0.75 1.00 1.25 0.25 ...

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... LT1576/LT1576 ABSOLUTE MAXIMUM (Note 1) Input Voltage .......................................................... 25V BOOST Pin Above Input Voltage ............................. 10V SHDN Pin Voltage ..................................................... 7V BIAS Pin Voltage ...................................................... 7V FB Pin Voltage (Adjustable Part) ............................ 3.5V FB Pin Current (Adjustable Part) ............................ 1mA SYNC Pin Voltage ..................................................... 7V Operating Junction Temperature Range LT1576C ............................................... 125 C LT1576I ........................................... – 125 C Storage Temperature Range ................ – ...

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... Note 10: Minimum on-time is 400ns typical. For a 200kHz operating frequency this means the minimum duty cycle is 8%. In frequency foldback mode, the effective duty cycle will be less than 8%. ) with a fraction of BIAS SI = 1.16mA. TOT and BIAS IN LT1576/LT1576-5 + 5V, switch open, unless otherwise noted. IN MIN TYP MAX 8 180 200 ...

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... LT1576/LT1576 TYPICAL PERFORMANCE CHARACTERISTICS Switch Drop 0.5 125 C 0 0.3 –20 C 0.2 0 0.50 0.75 1.00 1.25 1.50 0.25 SWITCH CURRENT (A) 1576 G01 Shutdown Pin Bias Current 4 AT 2.44V STANDBY THRESHOLD (CURRENT FLOWS OUT OF PIN – 125 –50 100 JUNCTION TEMPERATURE ( C) 1576 G04 Standby Thresholds 2 ...

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... Maximum Load Current 3.3V OUT 1. 0.75 0.50 0. 3.3V OUT INPUT VOLTAGE (V) 1576 G17 LT1576/LT1576-5 Frequency Foldback 250 SWITCHING FREQUENCY 200 150 100 50 FEEDBACK PIN CURRENT 0 1.0 0 0.5 1.5 FEEDBACK VOLTAGE (V) Maximum Load Current 10V OUT 1. 10V OUT 1. ...

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... LT1576/LT1576 TYPICAL PERFORMANCE CHARACTERISTICS BOOST Pin Current 0.50 0.25 SWITCH CURRENT ( PIN FUNCTIONS V (Pin 1): The switch pin is the emitter of the on-chip SW power NPN switch. This pin is driven up to the input pin voltage during switch on time. Inductor current drives the switch pin negative during switch off time ...

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... The current fed system will have 90 phase shift at a much lower frequency, but will not have the additional 90 shift until well beyond the LC resonant frequency. This makes LT1576/LT1576-5 SYNC (Pin 8): The SYNC pin is used to synchronize the internal oscillator to an external signal directly logic compatible and can be driven with any signal between 10% and 90% duty cycle ...

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... FB pin. Please read both parts before committing to a final design. The fixed 5V LT1576-5 has internal divider resis- tors and the FB pin is renamed SENSE, connected directly to the output. ...

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... LT1576 to lose control of current limit. TO FREQUENCY SHIFTING 1.4V Q1 ERROR AMPLIFIER + 1.21V – SYNC CIRCUIT Figure 2. Frequency and Current Limit Foldback LT1576/LT1576-5 pin to a voltage less than its OUTPUT 1576 F02 9 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION The internal circuitry which forces reduced switching frequency also causes current to flow out of the feedback pin when output voltage is low. The equivalent circuitry is shown in Figure completely off during normal operation. If the FB pin falls below 0.7V, Q1 begins to conduct current and reduces frequency at the rate of approximately 1kHz/ A ...

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... Keep in mind that all good things like high efficiency, low profile, and high tempera- ture operation will increase cost, sometimes dramati- cally. Get a quote on the cheapest unit first to calibrate yourself on price, then ask for what you really want. LT1576/LT1576 OUT ...

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... LT1576/LT1576 APPLICATIONS INFORMATION 5. After making an initial choice, consider the secondary things like output voltage ripple, second sourcing, etc. Use the experts in the Linear Technology’s applica- tions department if you feel uncertain about the final choice. They have experience with a wide range of inductor types and can tell you about the latest devel- opments in low profile, surface mounting, etc ...

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... Typical forward voltage is 0.42V at 1A. The diode conducts current only during switch off time. Peak reverse voltage is equal to regulator input voltage. Average forward current in normal operation can be calculated from AVG LT1576/LT1576 ESR ESL P-P dt =10V 5V ESR = 0 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION This formula will not yield values higher than 1A with maximum load current of 1.25A unless the ratio of input to output voltage exceeds 5:1. The only reason to consider a larger diode is the worst-case condition of a high input voltage and overloaded (not shorted) output. Under short- ...

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... 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 13.5V 12V. Let can be added to FB LT1576/LT1576-5 OUTPUT V SW STANDBY + TOTAL SHUTDOWN 1576 F04 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION SWITCH NODE CONSIDERATIONS For maximum efficiency, switch rise and fall times are made as short as possible. To prevent radiation and high frequency resonance problems, proper layout of the com- ponents connected to the switch node is essential. B field (magnetic) radiation is minimized by keeping catch diode, switch pin, and input bypass capacitor leads as short as possible ...

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... Ripple current INDUCTOR CURRENT ratings on the capacitor must be observed to ensure reliable operation. In many cases it is necessary to parallel two capacitors to obtain the required ripple rating. Both 1374 F08 capacitors must be of the same value and manufacturer to LT1576/LT1576 Rise OUT IN 17 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION guarantee power sharing. The actual value of the capacitor in microfarads is not particularly important because at 200kHz, any value above essentially resistive. RMS ripple current rating is the critical parameter. Actual RMS current can be calculated from RIPPLE RMS ...

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... By contrast, the LT1576 uses a “current mode” architecture to help alleviate phase shift created by the = 1A: OUT inductor. The basic connections are shown in Figure 9. Figure 10 shows a Bode plot of the phase and gain of the power section of the LT1576, measured from the V LT1576/LT1576 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION the output. Gain is set by the 1.5A/V transconductance of the LT1576 power section and the effective complex impedance from output to ground. Gain rolls off smoothly above the 160Hz pole frequency set by the 100 F output capacitor. Phase drop is limited to about 85 . Phase recovers and gain levels off at the zero frequency ( 16kHz) set by capacitor ESR (0 ...

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... C set at one-fifth of switching frequency so that it provides significant attenuation of switching ripple, but does not add unacceptable phase shift at loop unity-gain frequency. With R = 15k LT1576/LT1576-5 is held to less than 100mV C ripple voltage when R is added to the large compared to the reactance ...

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... LT1576/LT1576 APPLICATIONS INFORMATION How Do I Test Loop Stability? The “standard” compensation for LT1576 is a 100pF capacitor for C , with While this compensation C C will work for most applications, the “optimum” value for loop compensation components depends, to various ex- tent, on parameters which are not well controlled ...

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... LT1576’s 1.5A maximum switch current, even with large inductor values. The buck converter in comparison, delivers current to the output as a triangular wave superimposed level equal to load current, and load current can approach 1.5A LT1576/LT1576-5 D1 1N4148 C2 L1* ...

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... LT1576/LT1576 APPLICATIONS INFORMATION with large inductors. Output ripple voltage for the positive- to-negative converter will be much higher than a buck converter. Ripple current in the output capacitor will also be much higher. The following equations can be used to calculate operating conditions for the positive-to-negative converter ...

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... AVX type TPS “D” or “E” size surface mount solid tantalum capacitors, but the final capacitor chosen must be looked at carefully for ESR characteristics OUT LT1576/LT1576 ...

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... LT1576/LT1576 APPLICATIONS INFORMATION Ripple Current in the Input and Output Capacitors Positive-to-negative converters have high ripple current in both the input and output capacitors. For long capacitor lifetime, the RMS value of this current must be less than the high frequency ripple current rating of the capacitor. ...

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... TYP 0.014 – 0.019 (0.355 – 0.483) TYP LT1576/LT1576 0.150 – 0.157** (3.810 – 3.988 0.004 – 0.010 (0.101 – 0.254) 0.050 (1 ...

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... LT1576/LT1576-5 U TYPICAL APPLICATION Dual Output SEPIC Converter The circuit in Figure 17 generates both positive and negative 5V outputs with a single piece of magnetics surface mount inductor from Coiltronics manufactured with two identical windings that can be connected in series or parallel. The topology for the 5V output is a standard buck converter. The – ...