LT1956-5 Linear Technology, LT1956-5 Datasheet

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... A shutdown pin reduces supply current and the device can be externally synchronized from 580kHz to 700kHz with a logic level input. The LT1956/LT1956-5 are available in fused-lead 16-pin SSOP and thermally enhanced TSSOP packages. , LTC and LT are registered trademarks of Linear Technology Corporation. *U.S. PATENT NO. 6,498,466 MMSD914TI 0 ...

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... LT1956/LT1956 ABSOLUTE AXI U RATI GS Input Voltage (V ) ................................................. 60V IN BOOST Pin Above SW ............................................ 35V BOOST Pin Voltage ................................................. 68V SYNC, SENSE Voltage (LT1956-5) ........................... 7V SHDN Voltage ........................................................... 6V BIAS Pin Voltage .................................................... 30V FB Pin Voltage/Current (LT1956) ................... 3.5V/2mA U PACKAGE/ORDER I FOR ATIO TOP VIEW 1 GND 16 GND SHDN SYNC ...

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... Note 10: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125 C when overtemperature protection is active. Continuous operation above the specified maximum operating junction ): BIAS temperature may impair device reliability. = 2.9mA 2.4mA. TOTAL LT1956/LT1956 MIN TYP MAX = 4.1V 1 SENSE 0 ...

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... LT1956/LT1956 TYPICAL PERFOR A CE CHARACTERISTICS Switch Peak Current Limit 2.5 TYPICAL 2.0 GUARANTEED MINIMUM 1.5 1 100 DUTY CYCLE (%) 1956 G01 Lockout and Shutdown Thresholds 2.4 LOCKOUT 2.0 1.6 1.2 0.8 START-UP 0.4 SHUTDOWN 0 –50 – 100 125 JUNCTION TEMPERATURE ( C) 1956 G04 Error Amplifier Transconductance 2500 ...

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... T = 125 C J 350 300 250 200 150 T = – 100 0.5 1 1.5 SWITCH CURRENT (A) 1766 G14 LT1956/LT1956-5 BOOST Pin Current 0.5 1 1.5 SWITCH CURRENT (A) 1956 G12 Switch Minimum ON Time vs Temperature 600 500 400 300 ...

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... LT1956/LT1956 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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... V CC CURRENT COMPARATOR SLOPE COMP ANTISLOPE COMP 500kHz S OSCILLATOR FLIP-FLOP FOLDBACK V C(MAX) Q3 CURRENT CLAMP LIMIT CLAMP Figure 1. LT1956 Block Diagram LT1956/LT1956-5 R SENSE BOOST DRIVER S POWER CIRCUITRY SWITCH 2 SW FREQUENCY FOLDBACK ERROR AMPLIFIER – 2000 Mho m + 1.22V GND ...

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... FB pin. Please read both parts before committing to a final design. The 5V fixed output voltage part (LT1956-5) has internal divider resistors and the FB pin is renamed SENSE, connected directly to the output. ...

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... The following equations will help in choosing the required 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. LT1956/LT1956 OUTPUT 5V ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO Peak-to-peak output ripple voltage is the sum of a triwave (created by peak-to-peak ripple current (I and a square wave (created by parasitic inductance (ESL) and ripple current slew rate). Capacitive reactance is assumed to be small compared to ESR or ESL ESR ...

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... The current rating P conditions, use PEAK ( Reduced Inductor Value and Discontinuous Mode If the smallest inductor value is of the most importance to a converter design, in order to reduce inductor size/cost, discontinuous mode may yield the smallest inductor LT1956/LT1956-5 Continuous Mode ) – OUT F ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO solution. The maximum output load current in discontinu- ous 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 ( this mode, inductor current falls to zero before LP-P the next switch turn-on (see Figure 8) ...

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... Unlike the input capacitor, RMS ripple current in the output capacitor is normally low enough that ripple cur- rent rating is not an issue. The current waveform is triangular with a typical value of 125mA to calculate this is: LT1956/LT1956-5 and the output voltage IN OUT )] ratios > soft-start circuit should be used ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO Output capacitor ripple current (RMS OUT IN I RIPPLE RMS ( ) Ceramic Capacitors Ceramic capacitors are generally chosen for their good high frequency operation, small size and very low ESR (effective series resistance). Their low ESR reduces ...

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... Keep the connections from the resistors to the shutdown pin short and make sure that interplane or surface capaci- tance to the switching nodes are minimized. If high resistor values are used, the shutdown pin should be LT1956/LT1956-5 10k or less. If shutdown LO can be raised to 100k, but the error ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO INPUT bypassed with a 1000pF capacitor to prevent coupling problems from the switch node. If hysteresis is desired in the undervoltage lockout point, a resistor R added to the output node. Resistor values can be calcu- lated from ...

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... LT1956 BOOST BIAS C GND GND Figure 6. Suggested Layout LT1956/LT1956-5 LT1956 L1 HIGH FREQUENCY CIRCULATING PATH Figure 5. High Speed Switching Path GND FOR THE FE PACKAGE, SOLDER THE EXPOSED PAD TO THE COPPER GROUND PLANE UNDERNEATH THE DEVICE V OUT ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO Board layout also has a significant effect on thermal resis- tance. For the GN package, Pins and 16, GND, are a continuous copper plate that runs under the LT1956 die. This is the best thermal path for heat out of the package. ...

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... This should be done with minimal device power (low 0V]) in order to calibrate SYNC pin resistance with C ambient (oven) temperature. LT1956/LT1956 – ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO Note: Some of the internal power dissipation in the IC, due to BOOST pin voltage, can be transferred outside of the IC to reduce junction temperature by increasing the voltage drop in the path of the boost diode D2 (see Figure 9). This reduction of junction temperature inside the IC will allow higher ambient temperature operation for a given set of conditions ...

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... First, the combination of output capacitor ESR and R stop the loop rolling off altogether. Second, if the loop gain is not rolled off sufficiently at the switching frequency, output ripple will perturb the V unstable duty cycle switching similar to subharmonic LT1956/LT1956-5 compensation blocks, the error ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO LT1956 CURRENT MODE SW POWER STAGE ERROR g = 2mho m AMPLIFIER – 2000 mho + R 1.22V O 200k GND Figure 10. Model for Loop Response oscillations. If needed, an additional capacitor (C added across the R /C network from the V ...

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... The circuit in Figure 14a generates both positive and negative 5V outputs with all components under 3mm height. The topology for the 5V output is a standard buck 9 5 converter. The –5V output uses a second inductor L2 diode D3 and output capacitor C6. The capacitor C4 LT1956/LT1956-5 MMSD914TI 5V, 1A ALTERNATE SUPPLY R1 15.4k ...

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... LT1956/LT1956 APPLICATIO S I FOR ATIO 12V (TRANSIENTS TO 36V) C3 2.2 F 50V CERAMIC GND *SUMIDA CDRH4D28-150 **SEE FIGURE 14c FOR V LOAD CURRENT RELATIONSHIP † IF LOAD CAN GO TO ZERO, AN OPTIONAL PRELOAD OF 500 CAN BE USED TO IMPROVE REGULATION 500 450 400 350 300 ...

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... If R1 36.5k load current is higher, use the continuous mode formula. Output current where continuous mode is needed 100 F 20V TANT R2 I 4.12k CONT OUTPUT** –12V, 0.25A 1956 F15 Minimum inductor discontinuous mode: L MIN LT1956/LT1956 OUT I – OUT ...

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... LT1956/LT1956-5 PACKAGE DESCRIPTIO Minimum inductor continuous mode OUT L MIN – OUT P OUT For a 12V to –12V converter using the LT1956 with peak switch current of 1.5A and a catch diode of 0.63V CONT For a load current of 0.25A, this says that discontinuous ...

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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 LT1956/LT1956-5 4.90 – 5.10* (.193 – .201) 3.58 (.141) 16 1514 2.94 6.40 (.116) BSC ...

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... LT1956/LT1956-5 PACKAGE DESCRIPTIO .254 MIN .0165 .0015 RECOMMENDED SOLDER PAD LAYOUT .007 – .0098 (0.178 – 0.249) .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" ...