LT3798 LINER [Linear Technology], LT3798 Datasheet
LT3798
Available stocks
Related parts for LT3798
LT3798 Summary of contents
Page 1
... The input range can be scaled up or down, depending mainly on the choice of external components. Efficiencies higher than 86% can be achieved with output power levels up to 100W. In addition, the LT3798 can easily be designed into high DC input applications. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation ...
Page 2
... VC, OVP, COMP .........................................................4V SENSE ......................................................................0.4V V .................................................................1mA IN_SENSE DCM .......................................................................±3mA Operating Temperature Range (Note 2) LT3798E/LT3798I................................... –40°C to 125°C Storage Temperature Range .................. –65°C to 150°C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LT3798EMSE#PBF LT3798EMSE#TRPBF LT3798IMSE#PBF LT3798IMSE#TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. ...
Page 3
... Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3798E is guaranteed to meet specified performance from 0°C to 125°C junction temperature. Specification over the –40°C and l The denotes the specifications which apply over the full operating = 25° ...
Page 4
... LT3798 TYPICAL PERFORMANCE CHARACTERISTICS EN/UVLO Threshold vs Temperature 1.3 1.28 RISING 1.26 1.24 FALLING 1.22 1.2 – 100 125 150 –25 TEMPERATURE (°C) 3798 G01 V vs Temperature REF 2.100 2.075 2.050 2.025 V = 24V WITH NO LOAD IN 2.000 1.975 V = 24V WITH 200μA LOAD IN 1.950 1.925 1.900 –50 – ...
Page 5
... Leakage Inductance Blanking Time vs SENSE Current Limit Threshold 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0 SENSE CURRENT LIMIT THRESHOLD (mV) 210 230 250 270 190 3798 G13 LT3798 T = 25°C, unless otherwise noted Shunt Voltage vs Temperature 1mA SHUNT 41.5 41 40 – – ...
Page 6
... EN/UVLO (Pin 12): Enable/Undervoltage Lockout. A resis- tor divider connected to V the minimum input voltage at which the LT3798 will turn on. When below 1.25V, the part will draw 60μA with most of the internal circuitry disabled and a 10μA hysteresis current will be pulled out of the EN/UVLO pin ...
Page 7
... INTERNAL REG + ONE A2 SHOT – + CURRENT COMPARATOR 600mV + – A1 – SW1 LOW OUTPUT A6 CURRENT OSCILLATOR MULTIPLIER LT3798 (Pin 16): Line Voltage Sense Pin. The pin is with a 25k resistor RECTIFIED L1A L1B N – A7 INTV R11 GATE ...
Page 8
... A comparator is used to detect discontinu- ous conduction mode (DCM) with a cap connected to the third winding. The part features a 1.9A gate driver. The LT3798 is designed for both off-line and DC applica- tions. The EN/UVLO and a resistor divider can be configured for a micropower hysteretic start-up. In the Block Diagram used to stand off the high voltage supply voltage ...
Page 9
... In this isolated case, the output current information is not available so instead the LT3798 calculates it using the in- formation available on the primary side of the transformer. The output current may be calculated by taking the average of the output diode current ...
Page 10
... V to INTV instead of the AC line voltage. IN_SENSE CC Startup The LT3798 uses a hysteretic start-up to operate from high offline voltages. A resistor connected to the supply voltage protects the part from high voltages. This resistor is connected to the V pin on the part and bypassed with IN a capacitor. When the resistor charges the V ...
Page 11
... Critical Conduction Mode Operation Critical conduction mode is a variable frequency switching scheme that always returns the secondary current to zero with every cycle. The LT3798 relies on boundary mode and discontinuous mode to calculate the critical current because the sensing scheme assumes the secondary current returns to zero with every cycle ...
Page 12
... The minimum voltage of the switch node during this discontinuous ring is V The LT3798 turns the switch back on at this time, during the discontinuous switch waveform, by sensing when the slope of the switch waveform goes from negative to positive using the dv/dt detector ...
Page 13
... To determine the power dissipated in the snubber resistor from capacitive losses, measure the drain voltage immediately before the MOS- FET turns on and use the following equation relating that LT3798 ) and snubber capacitance PERIOD(SNUBBED below, and the resultant waveforms are ...
Page 14
... LT3798. Table 1 shows the details of several of these 2 /2 transformers. Loop Compensation The voltage feedback loop is a traditional GM error ampli- fier ...
Page 15
... OPERATION MOSFET and Diode Selection With a strong 1.9A gate driver, the LT3798 can effectively drive most high voltage MOSFETs. A low Qg MOSFET is recommended to maximize efficiency. In most applications, the R should be chosen to limit the temperature rise DS(ON) of the MOSFET. The drain of the MOSFET is stressed to V • N ...
Page 16
... Figure 6. Switching Waveforms When Output Short-Circuits 16 Usage with DC Input Voltage The LT3798 is flexible enough to operate well from low voltage to very high voltage DC input voltage applications. When the supply voltage is less than 40V, the startup re- sistor is not needed and the part's V UVLO to shutdown directly to the supply voltage ...
Page 17
... V REF R11 R9 SENSE CTRL3 100k 40.2k INTV CTRL2 CC CTRL1 GND OVP + – VC COMP COMP R12 R10 221k 16.5k C3 C7, 0.1μF 2.2μF LT3798 4:1:1 R14 D4 90. C10 R15 C6 560μ F 4.99k 22pF × R16 20Ω 0.05Ω C8 4.7μF 2.2nF “Y1 CAP” 3798 TA02 ...
Page 18
... 47Ω 499k 100k C2 0.22μ 499k 100k 22pF C5 10μ F R13 D3 33k R5 V DCM IN 2. IN_SENSE EN/UVLO R6 LT3798 301k V REF R11 R9 CTRL3 GATE 100k 40.2k CTRL2 SENSE INTV CTRL1 CC OVP GND + – R12 R10 VC COMP COMP 221k 31.6k C3 C7, 0.1μF 1μF ...
Page 19
... MAX SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3798 8 0.35 REF 1.651 ± 0.102 (.065 ± .004) 0.12 REF DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 9 NO MEASUREMENT PURPOSE 0.280 ± ...
Page 20
... Wide DC Input Industrial Power Supply R17 R7 D2 20Ω 6. 6.8k 15pF C5 10μ F R13 D3 15k R14 V DCM 100k IN_SENSE R15 EN/UVLO C6 LT3798 5.9k 22pF V REF CTRL3 GATE CTRL2 SENSE INTV CTRL1 CC C9 OVP 4.7μF GND + – VC COMP COMP C7, 22nF C3 0.1μF R3 16.2k M1: ...