lt3958 Linear Technology Corporation, lt3958 Datasheet
lt3958
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lt3958 Summary of contents
Page 1
... The fi xed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. The operating frequency of LT3958 can be set with an external resistor over a 100kHz to 1MHz range, and can be synchronized to an external clock using the SYNC pin. A minimum operating supply voltage of 5V, and a low shutdown quiescent current of less than 1μ ...
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... LT3958EUHE#PBF LT3958EUHE#TRPBF LT3958IUHE#PBF LT3958IUHE#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi label on the shipping container. For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: ...
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... 1.5V, FBX = 0V, Current Out of Pin FBX = 1.7V FBX = –0.85V R = 140k to SGND, FBX = 1.6V 1. 41.2k to SGND, FBX = 1.6V 1. 10.5k to SGND, FBX = 1.6V 1.5V T FBX = 1. 0V, Current Out of Pin Falling INTV CC UVLO Hysteresis LT3958 MIN TYP MAX UNITS 0.1 1 μA 6 μA 1.6 2.2 mA 350 400 μ ...
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... CC I Drops Below 1μA VIN EN/UVLO = 1.15V EN/UVLO = 1.33V Note 3: The LT3958 is tested in a feedback loop which servos V reference voltages (1.6V and –0.8V) with the VC pin forced to 1.3V. Note 4: FBX overvoltage lockout is measured regulated V Note 5: For 5V < V Note 6: EN/UVLO = 1.33V when V Negative Feedback Voltage ...
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... TEMPERATURE (°C) EN/UVLO Current vs Voltage EN/UVLO VOLTAGE (V) LT3958 T = 25°C, unless otherwise noted. A Normalized Switching Frequency vs FBX 120 100 –0.8 –0.4 0 0.4 900 1000 FBX VOLTAGE (V) 3958 G05 SW Pin Current Limit vs Duty Cycle 4 ...
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... LT3958 TYPICAL PERFORMANCE CHARACTERISTICS INTV vs Temperature CC 7.4 7.3 7.2 7.1 7.0 –50 – 100 TEMPERATURE (°C) 3958 G13 INTV Dropout Voltage CC vs Current, Temperature 900 125°C 800 700 75°C 600 25°C 500 400 0°C 300 –40°C 200 100 INTV ...
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... If this feature is used program a switching frequency 20% slower than the SYNC pulse frequency. Tie the SYNC pin to SGND if this pin can be locally feature is not used. SYNC is ignored when FBX is close IN to SGND. LT3958 and regulated to IN must be bypassed to SGND with less than 11.5V. ...
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... A12 + –0.88V + 1.6V A1 – – –0.8V FREQUENCY FOLDBACK FBX OUT Figure 1. LT3958 Block Diagram Working as a SEPIC Converter EN/UVLO 25 A10 – 2μA 1.22V 2.5V INTERNAL REGULATOR AND UVLO I S2 12.8V + 10μA UVLO A9 – ...
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... APPLICATIONS INFORMATION Main Control Loop The LT3958 uses a fi xed frequency, current mode control scheme to provide excellent line and load regulation. Op- eration can be best understood by referring to the Block Diagram in Figure 1. The start of each oscillator cycle sets the SR latch (SR1) and turns on the internal power MOSFET switch M1 through driver G2. The switch current fl ...
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... The INTV CC (UV) threshold is 3.75V (typical), with 0.15V hysteresis, to ensure that the internal MOSFET has suffi cient gate drive voltage before turning on. The logic circuitry within the LT3958 is also powered from the internal INTV supply. The INTV overvoltage threshold is set to be 12.8V CC (typical) to protect the gate of the power MOSFET ...
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... MOSFET. This time is generally about 250ns (typical) (see Minimum On-Time in the Electrical Characteristics table). In each switching cycle, the LT3958 keeps the power switch off for at least 200ns (typical) (see Minimum Off-Time in the Electrical Characteristics table). The minimum on-time, minimum off-time and the switching frequency defi ...
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... INTV < 3.55V CC 3. Thermal lockout Any of these three faults will cause the LT3958 to stop switching immediately. The SS pin will be discharged by Q3. When all faults are cleared and the SS pin has been discharged below 0.2V, a 10μA current source I charging the SS pin, initiating a soft-start operation. ...
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... T S Figure 3. The Switch Current During a Switching Cycle Due to the current limit (minimum 3.3A) of the internal power switch, the LT3958 should be used in the applica- tions that the switch peak current I SW(PEAK) state normal operation is lower than 3. suffi cient margin (10% or higher is recommended). ...
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... SEPIC and inverting converters. Boost Converter: Switch Duty Cycle and Frequency The LT3958 can be confi gured as a boost converter for the applications where the converter output voltage is higher than the input voltage. Remember that boost con- verters are not short-circuit protected ...
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... A low ESR capacitor is recommended, although it is not as critical as for the output capacitor. The RMS input capacitor ripple current for a boost con- verter is: = 0.3 • ΔI I RMS(CIN) LT3958 OFF V COUT RINGING DUE TO TOTAL INDUCTANCE (BOARD + CAP) ESR ...
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... LT3958 APPLICATIONS INFORMATION FLYBACK CONVERTER APPLICATIONS The LT3958 can be confi gured as a fl yback converter for the applications where the converters have multiple outputs, high output voltages or isolated outputs. Figure 6 shows a simplifi ed fl yback converter. The fl yback converter has a very low parts count for mul- ...
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... IN(MIN) OUT N S Due to the current limit of its internal power switch, the LT3958 should be used in a fl yback converter whose maxi- mum output current ( less than the maximum O(MAX) output current capability by a suffi cient margin (10% or higher is recommended): ...
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... I RMS(CIN),CONTINUOUS SEPIC CONVERTER APPLICATIONS The LT3958 can be confi gured as a SEPIC (single-ended primary inductance converter), as shown in Figure 1. This topology allows for the input to be higher, equal, or lower than the desired output voltage. The conversion ratio as a function of duty cycle is: ...
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... IN I SW(MAX) Due to the current limit of its internal power switch, the LT3958 should be used in a SEPIC converter whose maximum output current (I current capability by a suffi cient margin (10% or higher is recommended): I O(MAX) The inductor ripple currents ΔI ...
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... I RMS(CDC) A low ESR and ESL, X5R or X7R ceramic capacitor works well for safety IN(MAX) INVERTING CONVERTER APPLICATIONS The LT3958 can be confi gured as a dual-inductor inverting topology, as shown in Figure 8. The V V − V OUT continuous conduction mode (CCM). θJC ...
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... A low ESR and ESL, X5R or X7R ceramic capacitor works well for C Board Layout The high power and high speed operation of the LT3958 demands careful attention to board layout and component placement. Careful attention must be paid to the internal power dissipation of the LT3958 at high input voltages, high switching frequencies, and high internal power switch currents to ensure that a junction temperature of 125° ...
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... Place the divider resis- tors near the LT3958 in order to keep the high impedance FBX node short. Figure 9 shows the suggested layout of the 48V V converter (see the Typical Applications section) ...
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... C 10nF 3958 TA02a High Voltage Flyback Power Supply T1 1:10 47μF • 16V 2 • 220pF 22Ω 31. GND IN EN/UVLO FBX 10k LT3958 SGND SENSE1 SYNC SENSE2 INTV 140k 0.1μF 100kHz 10k 10nF 100pF C : MURATA GRM32ER61C476M TDK C3225X7R2J683K OUT D1: VISHAY SILICONIX GSD2004S DUAL DIODE CONNECTED IN SERIES T1: TDK DCT15EFD-U44S003 Effi ...
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... MURATA GRM32ER61C226KE20 OUT D1: VISHAY SILICONIX 10MQ100N L1A, L1B: COILTRONICS DRQ125-220 0.5V/DIV I OUT 0.5A/DIV 800 1000 3958 TA04b 10V/DIV 20V/DIV L1A 2A/DIV 3958 TA04d LT3958 D1 V OUT 12V C 1A OUT 22μF L1B 16V • X5R 2 105k 15.8k 3958 TA04a Load Step Waveforms ...
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... L1B 2A/DIV 5ms/DIV 26 10V to 60V Input, –12V Output Inverting Converter C DC 2.2μF, 100V L1A X7R 2.2μF 392k 100V X5R EN/UVLO GND 66.5k LT3958 SGND SENSE1 SYNC SENSE2 FBX INTV 41.2k C VCC 10k 300kHz 4.7μF 0.47μF 10V X5R 10nF MURATA GRM32ER72A225KA35L ...
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... BSC 2.00 REF 5.10 0.05 6.50 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.75 0. 0.10 TYP 28 27 2.00 REF 0.200 REF 0.00 – 0.05 LT3958 0.70 0. PACKAGE OUTLINE 13 12 PIN 1 NOTCH 1.50 REF 0.35 45 CHAMFER 1 2 1.88 0. ...
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... IN 10V TO 40V • 0.1μ 1.8k 50V 4.7μF 1W 50V • X5R D SN 200k V SW GND IN EN/UVLO 32.4k LT3958 SGND SENSE1 SYNC SENSE2 FBX INTV 63.4k 0.47μF 10k 200kHz 100pF 10nF T1: COILTRONICS VP2-0066 RELATED PARTS PART NUMBER DESCRIPTION LT3580 Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start and Synchronization ...