LT1578IS8 Linear Technology, LT1578IS8 Datasheet

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... The new SO-8 package includes a fused ground lead that significantly reduces the thermal resistance of the device to extend the ambient operating temperature range. Standard surface mount external parts can be used including the inductor and capacitors. , LTC and LT are registered trademarks of Linear Technology Corporation 0.33 F 1N914 ...

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... I 1. INFORMATION ORDER PART NUMBER TOP VIEW 8 SYNC LT1578CS8 SHDN 7 LT1578IS8 FB/SENSE 6 LT1578CS8-2 LT1578IS8-2.5 S8 PACKAGE S8 PART MARKING 1578 157825 1578I 578I25 + 5V, switch open, unless otherwise noted. IN MIN TYP MAX 1.195 1.21 1.225 1.18 1.24 2.46 2.5 2.54 2.44 2.56 5.7 9 ...

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ELECTRICAL CHARACTERISTICS ture range, otherwise specifications are at T PARAMETER Boost Current (Note 5) V Supply Current (Note 6) IN Shutdown Supply Current Lockout Threshold Shutdown Thresholds Synchronization Threshold Synchronizing Range SYNC Pin Input Resistance Note 1: Absolute Maximum Ratings ...

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LT1578/LT1578-2 TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Pin Bias Current (V = Lockout Threshold) SHDN 4 AT 2.44V STANDBY THRESHOLD (CURRENT FLOWS OUT OF PIN –50 – 100 125 JUNCTION TEMPERATURE ( ...

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W U TYPICAL PERFORMANCE CHARACTERISTICS Switching Frequency 240 220 200 180 160 –50 – 100 125 JUNCTION TEMPERATURE ( C) 1576 G13 Maximum Output Current OUT 1 1.4 ...

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LT1578/LT1578-2 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 ...

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W BLOCK DIAGRAM The LT1578 is a constant frequency, current mode buck converter. 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 ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT1578 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 ...

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U U APPLICATIONS INFORMATION In addition to lower switching frequency, the LT1578 also operates at lower switch current limit when the feedback pin voltage drops below 0.7V Figure 2 performs this function by clamping the V pin to ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION Note that there is less load current available at the higher input voltage because inductor ripple current increases. This is not always the case. Certain combinations of inductor value and input voltage range may yield ...

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... 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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LT1578/LT1578-2 APPLICATIONS INFORMATION Output Capacitor The output capacitor is normally chosen by its Effective Series Resistance (ESR), because this is what determines output ripple voltage. To get low ESR takes volume , so physically smaller capacitors have high ...

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U U APPLICATIONS INFORMATION Peak-to-peak output ripple voltage is the sum of a triwave created by peak-to-peak ripple current times ESR, and a square wave created by parasitic inductance (ESL) and ripple current slew rate. Capacitive reactance is assumed to ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION boost capacitor. This normally means that peak BOOST pin voltage is equal to input voltage plus output voltage, but when the boost diode is connected to the regulator input, peak BOOST pin voltage is equal ...

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U U APPLICATIONS INFORMATION conditions. UVLO helps prevent the regulator from oper- ating at source voltages where these problems might occur. Threshold voltage for lockout is about 2.42V. A 3.5 A bias current flows out of the pin at threshold. ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION CONNECT OUTPUT CAPACITOR DIRECTLY TO HEAVY GROUND C1 MINIMIZE AREA OF CONNECTIONS L1 TO SWITCH NODE AND BOOST NODE SW KEEP INPUT D1 CAPACITOR AND CATCH C3 V DIODE CLOSE IN TO REGULATOR AND TERMINATE ...

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U U APPLICATIONS INFORMATION PARASITIC RESONANCE Resonance or “ringing” may sometimes be seen on the switch node (see Figure 7). Very high frequency ringing following the switch voltage rise time is caused by switch/ diode/input capacitance lead inductance and diode ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION because at 200kHz, any value above essentially resistive. RMS ripple current rating is the critical param- eter. Actual RMS current can be calculated from RIPPLE RMS OUT OUT ...

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U U APPLICATIONS INFORMATION At power-up, when V is being clamped by the FB pin (see C Figure 2, Q2), the sync function is disabled. This allows the frequency foldback to operate in the shorted output con- dition. During normal ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION the output. Gain is set by the 1.5A/V transconductance of the LT1578 power section and the effective complex impedance from output to ground. Gain rolls off smoothly above the 160Hz pole frequency set by the ...

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U U APPLICATIONS INFORMATION Analog experts will note that around 7kHz, phase dips close to the zero phase margin line. This is typical of switching regulators, especially those that operate over a wide range of loads. This region of low ...

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LT1578/LT1578-2 APPLICATIONS INFORMATION How Do I Test Loop Stability? The “standard” compensation for LT1578 is a 100pF capacitor for C , with While this compensation will C C work for most applications, the “optimum” value ...

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U U APPLICATIONS INFORMATION The output of the regulator contains both the desired low frequency transient information and a reasonable amount of high frequency (200kHz) ripple. The ripple makes it difficult to observe the small transient two-pole, 100kHz ...

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LT1578/LT1578-2 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 ...

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U U APPLICATIONS INFORMATION inductor is therefore typically based on ensuring that peak switch current rating is not exceeded. This gives the lowest value of inductance that can be used, but in some cases (lower output load currents) it may ...

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LT1578/LT1578-2 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 ...

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... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...

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... SOT-23 Low Voltage Step-Down DC/DC Controller LTC1735 High Efficiency Step-Down Converter LT1777 Low Noise Step-Down Switching Regulator Burst Mode is a trademark of Linear Technology Corporation. Linear Technology Corporation 28 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com coupling losses. C4 provides a low impedance path to maintain an equal voltage swing in L1B, improving regu- lation ...