LTC1871 Linear Technology, LTC1871 Datasheet
LTC1871
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LTC1871 Summary of contents
Page 1
... Burst Mode operation at light loads, a low minimum ® Operation operating supply voltage of 2.5V and a low shutdown quiescent current make the LTC1871 ideally suited for battery-operated systems. For applications requiring constant frequency operation, Burst Mode operation can be defeated using the MODE/ SYNC pin. Higher output voltage boost, SEPIC and fly- ...
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... V in Percent FB(OV) FB(NOM) I Pin Load = 5 A (Note 5) TH Falling I Voltage (Note 5) TH Duty Cycle < 20 SENSE V = 30V SENSE U W ORDER PART NUMBER LTC1871EMS 10 SENSE INTV CC 7 GATE 6 GND MS PART MARKING = 120 C/ W LTSX MIN TYP MAX 2 ...
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... L Note 4: The dynamic input supply current is higher due to power MOSFET gate charging (Q • Note 5: The LTC1871 is tested in a feedback loop that servos V reference voltage with the I (the no load to full load operating voltage range for the I 1.23V). and power Note synchronized application, the internal slope compensation A gain is increased by 25% ...
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... LTC1871 W U TYPICAL PERFOR A CE CHARACTERISTICS FB Voltage vs Temp 1.25 1.24 1.23 1.22 1.21 –50 – 100 125 150 TEMPERATURE ( C) 1871 G01 Shutdown Mode (V) IN 1871 G04 Burst Mode I vs Temperature Q 500 400 300 200 100 0 100 125 150 – ...
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... TEMPERATURE ( C) 1871 G14 INTV Line Regulation CC 5.4 5.3 5.2 5 (V) IN 1871 G17 LTC1871 R vs Frequency T 1000 100 10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (kHz) 1871 G12 SENSE Pin Current vs Temperature 35 GATE HIGH ...
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... LTC1871 CTIO S RUN (Pin 1): The RUN pin provides the user with an accurate means for sensing the input voltage and pro- gramming the start-up threshold for the converter. The falling RUN pin threshold is nominally 1.248V and the comparator has 100mV of hysteresis for noise immunity. ...
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... SLOPE COMPENSATION OSC I OSC 50k OV BURST COMPARATOR + 0.30V EA – V-TO-I I LOOP 1.230V SLOPE 1.230V UV TO START-UP BIAS V REF CONTROL V IN LTC1871 RUN + 1 BIAS AND C2 START-UP CONTROL – 1.248V INTV CC GATE PWM LATCH 7 LOGIC S Q GND R CURRENT SENSE COMPARATOR + 10 C1 – ...
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... SW reset-dominant, the power MOSFET is actively held off for the duration of an output overvoltage condition. The LTC1871 can be used either by sensing the voltage drop across the power MOSFET or by connecting the SENSE pin to a conventional shunt resistor in the source of the power MOSFET, as shown in Figure 2. Sensing the ...
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... V OUT 50mV/DIV I L 5A/DIV 1871 F03 Figure 4. LTC1871 Low Output Current Operation with Burst Mode Operation Disabled (MODE/SYNC = INTV LTC1871 . If the I pin drops below 0.30V, DS(ON) TH burst clamp is removed, allowing the I TH pin is driven below 0 ...
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... internal, P-channel low dropout voltage regulator pro- duces the 5.2V supply which powers the gate driver and logic circuitry within the LTC1871, as shown in Figure 7. The INTV bypassed to ground immediately adjacent to the IC pins with a minimum of 4.7 F tantalum or ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the MOSFET gate driver ...
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... Figure 7. Bypassing the LDO Regulator and Gate Driver Supply As a result, high input voltage applications in which a large power MOSFET is being driven at high frequencies can cause the LTC1871 to exceed its maximum junction temperature rating. The junction temperature can be estimated using the following equations: ...
Page 12
... R1 of about 250k). Programming Turn-On and Turn-Off Thresholds with the RUN Pin The LTC1871 contains an independent, micropower volt- age reference and comparator detection circuit that re- mains active even when the device is shut down, as shown in Figure 8. This allows users to accurately program an input voltage at which the converter will turn on and off ...
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... This allows the user to obtain high output voltages from low input supply voltages. Boost Converter: The Peak and Average Input Currents The control circuit in the LTC1871 is measuring the input current (either by using the R DS(ON using a sense resistor in the MOSFET source), so the output current needs to be reflected back to the input in order to dimension the power MOSFET properly ...
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... MOSFET’s thermal resistances (R The gate drive voltage is set by the 5.2V INTV regulator. Consequently, logic-level threshold MOSFETs should be used in most LTC1871 applications. If low input voltage operation is expected (e.g., supplying power from Kool registered trademark of Magnetics, Inc. 1871 F09 ® ...
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... MOSFET as both a switching and a sensing element, care should be taken to ensure that the converter is capable of delivering the required load current DS(ON) over all operating conditions (line voltage and tempera- ture), and for the worst-case specifications for V 0.8 1.0 1871 F10 Figure 11. Normalized R LTC1871 1 – D MAX V • ) SENSE MAX ( ...
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... LTC1871 U U APPLICATIO S I FOR ATIO and the R of the MOSFET listed in the manufacturer’s DS(ON) data sheet. The power dissipated by the MOSFET in a boost converter is MAX ( ) P • R • FET – D MAX I O MAX ( ) • • • ...
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... MIN ( ) V IN MIN ( ) 12e. Output Voltage Ripple Waveform Figure 12. Switching Waveforms for a Boost Converter LTC1871 OUT OUT L 12a. Circuit Diagram I ...
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... Small-Signal Discretes (631) 543-7100 Burst Mode Operation and Considerations The choice of MOSFET R determines the load current at which the LTC1871 enters Burst Mode operation. When bursting, the controller clamps the peak inductor current to approximately: I BURST PEAK which represents about 20% of the maximum 150mV SENSE pin voltage ...
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... Although all dissipative elements in the circuit produce losses, four main sources usually account for the majority of the losses in LTC1871 application circuits The supply current into V ...
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... LTC1871 U U APPLICATIO S I FOR ATIO resistor value would be 10m , and the power dissi- pated in this resistor would be 514mW at maximum output current. Assuming an efficiency of 90%, this sense resistor power dissipation represents 1.3% of the overall input power. In other words, for this appli- cation, the use of V ...
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... PC Board Layout Checklist 1. In order to minimize switching noise and improve output load regulation, the GND pin of the LTC1871 should be connected directly to 1) the negative termi- nal of the INTV terminal of the output decoupling capacitors, 3) the ...
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... LTC1871 INTV FREQ GATE 5 6 MODE/ GND C SYNC VCC PSEUDO-KELVIN GROUND CONNECTION Figure 15. LTC1871 Boost Converter Layout Diagram SWITCH NODE IS ALSO THE HEAT SPREADER FOR L1, M1 OUT 1871 F14 SWITCH NODE GND C ...
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... LTC1871 is not shared with other converters. AC input current from another converter could cause substantial input voltage ripple, and this could interfere with the operation of the LTC1871. A few inches of PC trace or wire (L 100nH) between the C V should be sufficient to prevent current sharing IN problems ...
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... The maximum duty cycle of the LTC1871 is typically 92 SEPIC Converter: The Peak and Average Input Currents The control circuit in the LTC1871 is measuring the input current (either using the means of a sense resistor in the MOSFET source), so the output current needs to be reflected back to the input I in order to dimension the power MOSFET properly ...
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... SEPIC Converter: Power MOSFET Selection : The power MOSFET serves two purposes in the LTC1871 represents the main switching element in the power path, and its R V ...
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... LTC1871 U U APPLICATIO S I FOR ATIO MOSFET to ensure the V remains below the maximum DS rating for the device. During the MOSFET’s on-time, the control circuit limits the maximum voltage drop across the power MOSFET to about 150mV (at low duty cycle). The peak inductor ...
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... ESR or RMS current handling requirements of the application. Aluminum electrolytic and dry tantalum capacitors are both available in surface mount packages. In the case of tantalum critical that the capacitors have been surge tested for use in switching power supplies. An excellent LTC1871 • ) ...
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... LTC1871 U U APPLICATIO S I FOR ATIO choice is AVX TPS series of surface mount tantalum. Also, ceramic capacitors are now available with extremely low ESR, ESL and high ripple current ratings. SEPIC Converter: Input Capacitor Selection The input capacitor of a SEPIC converter is less critical ...
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... V = 12V 4. 15V 12V O 50 MODE = INTV 45 0.001 0.01 0.1 1 OUTPUT CURRENT (A) Figure 18b. SEPIC Efficiency vs Output Current LTC1871 V 1 SENSE MAX ( ) • • MAX ( ) 1 • • • • ...
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... V (AC) OUT 200mV/DIV I OUT 0.5A/DIV 50 s/DIV Figure 19. LTC1871 SEPIC Converter Load Step Response 6. The diode for this design must handle a maximum DC output current of 2A and be rated for a minimum reverse voltage 27V. A 3A, 40V diode IN OUT from International Rectifier (30BQ040) is chosen for its small size, relatively low forward drop and acceptable reverse leakage at high temp ...
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... F X5R 6.3V D1: INTERNATIONAL RECTIFIER 30BQ015 L1: TOKO DS104C2 B952AS-1R8N M1: SILICONIX/VISHAY Si9426 Output Efficiency at 2.5V and 3.3V Input 100 0.001 0.01 0.1 1 OUTPUT CURRENT (A) 1871 TA01b LTC1871 V IN 2. OUT OUT1 150 F C 6.3V OUT2 6.3V X5R 2 GND 1871 TA01a ...
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... VCC2 2 4.7 F 35V 0.007 X5R X5R L4: SUMIDA CEP125-5R6MC-HD L5: SUMIDA CEP125-0R3NC-ND D1, D2: ON SEMICONDUCTOR MBR2045CT M1, M2: INTERNATIONAL RECTIFIER IRLZ44NS 10 RUN SENSE LTC1871 8 FB INTV CC 7 FREQ GATE IN1 + VCC MODE/SYNC GND 4 16V 10V X5R X5R D1, D2: MBS120T3 ...
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... SILICONIX/VISHAY Si4840 TAIYO YUDEN JMK325BJ226MN Q1: PHILIPS BC847BF LMK316BJ475ML V OUT 100mV/DIV (AC) 2.2A I OUT 1A/DIV (DC) 0.5A 1871 TA02b Load Step Response 28V IN V OUT (AC) 2.2A 0.5A 250 s/DIV LTC1871 V 4.5V to 28V • 2.2 F L1* 25V X5R ( PEAK) C OUT1 330 F C 6.3V OUT2 L2* 6 ...
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... C 10k C C2 330pF C C1 10nF C : TDK C5750X5R1C476M TDK C5750X7R1E226M TDK C5750X5R0J107M OUT C : TAIYO YUDEN LMK316BJ475ML VCC RUN SENSE LTC1871 INTV FREQ GATE 5 6 MODE/SYNC GND C VCC R T 4.7 F 80.6k 10V 1% X5R R4 10k 10k 1% 1 LT1783 ...
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... BSC 4.88 0.10 DETAIL “A” (.192 .004) 0 – 6 TYP 0.53 0.01 (.021 .006) 1.10 (.043) DETAIL “A” MAX SEATING PLANE 0.17 – 0.27 (.007 – .011) LTC1871 0.497 0.076 (.0196 .003 REF 3.00 0.102 (.118 .004) NOTE 0.86 (.034) REF 0.13 0.05 (.005 .002) ...
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... LTC1871 U TYPICAL APPLICATIO 49.9k 150k 1nF C C2 100pF RUN I TH LTC1871 82k FREQ C C1 MODE/SYNC R 1nF T 120k f = 200kHz *COILTRONICS VP5-0155 (PRIMARY = 3 WINDINGS IN PARALLEL) RELATED PARTS PART NUMBER DESCRIPTION ® LT 1619 Current Mode PWM Controller LTC1624 Current Mode DC/DC Controller ...