lt3740 Linear Technology Corporation, lt3740 Datasheet
lt3740
Available stocks
Related parts for lt3740
lt3740 Summary of contents
Page 1
... The LT3740 has three current limit levels that can be chosen by connecting the RANGE pin to ground, open, and input respectively. ...
Page 2
... C RANGE = 0V RANGE = Open RANGE = 3300pF LOAD C = 3300pF LOAD C = 3300pF LOAD U W TOP VIEW ORDER PART NUMBER LT3740EDHC 14 XREF 13 SHDN 17 12 PGOOD 11 RANGE DFN PART MARKING 9 SWB DHC PACKAGE 3740 = 125°C, θ = 43°C/W JA MIN TYP MAX ● ...
Page 3
... LOAD I = 100μA PGOOD Note 2: The LT3740E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Transient Response LOAD STEP 0A TO 10A ...
Page 4
... LT3740 W U TYPICAL PERFOR A CE CHARACTERISTICS Shutdown vs Maximum V C 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0 0.5 1 1.5 2 2.5 SHUTDOWN (V) 3740 G07 PGOOD Threshold vs Temperature 770 760 750 740 730 720 710 –50 – TEMPERATURE (°C) 3740 G09b Error Amplifier Transconductance vs Temperature 400 390 380 370 360 ...
Page 5
... Connect the feedback resistor divider to this pin. V (Pin 16): Error Amplifier Compensation Pin. C Connect the external compensation RC to this pin. The current comparator threshold increases with the voltage of this pin. Exposed Pad (Pin 17): Ground. Must be soldered to PCB ground. LT3740 3740fa 5 ...
Page 6
... LT3740 W BLOCK DIAGRA SHDN + XREF 14 – – + 0.72V 12 PGOOD 6 7. – – Σ RAMP GENERATOR – REF 0.80V Σ RAMP GENERATOR V SWB – 1.2MHz OSCILLATOR SWITCH LOGIC – + 300KHz OSCILLATOR 8 BIAS 7 TGATE 6 SW ...
Page 7
... The tracking capability built into XREF can be used to implement another startup scheme. If less than 0.8V is applied to XREF , the LT3740 will use this voltage as the reference for regulation. Slowly ramping up the voltage at XREF forces the output to increase slowly, which limits the start-up current, as shown in Typical Performance Characteristics ...
Page 8
... SHDN signal, large load step-down transient response, or the output voltage being pulled up by some other power supply. The LT3740 has a reverse current comparator to limit the reverse current. During the on-time of the bottom MOSFET, when (V +)– ...
Page 9
... LT3740 delays the turn on of TGATE until BGATE is off. When the internal bottom MOSFET on signal comes, the LT3740 delays the turn on of BGATE until the SW node swings down to ground. In the case of small or negative inductor current that SW node cannot swing ...
Page 10
... U U APPLICATIO S I FOR ATIO Choose MOSFET Sensing or Resistor Sensing The LT3740 can use either the bottom MOSFET on- resistance or an external sensing resistor for current sensing. Simplicity and high efficiency are the benefits of using bottom MOSFET on-resistance. However, some MOSFETs have a wide on-resistance variation. As discussed previously, the gate-source voltage and the temperature also affect the MOSFET on-resistance ...
Page 11
... To dampen input voltage transients, add a small 5μF to 50μF aluminum electrolytic capacitor with an ESR in the range of 0.5Ω to 2Ω where: OUT LT3740 is primarily determined by the ESR OUT is approximately OUT ⎛ ⎞ 1 < ...
Page 12
... MOSFET junc- tion temperature and the resulting value of I heats the MOSFET switches. In the event of output short-circuit to ground, the LT3740 operates at maximum inductor current and minimum duty cycle. The actual inductor discharging voltage is the voltage drop on the parasitic resistors including bottom ...
Page 13
... Step-Up Converter Capacitor Selection The small size of ceramic capacitors makes them ideal for the output of the LT3740 step-up converter. X5R and X7R types are recommended because they retain their capaci- tance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1μ ...
Page 14
... LT3740 U U APPLICATIO S I FOR ATIO Design Example As a design example, take a supply with the following specifications 20V (15V nominal ± 5 10A. First, choose the inductor for about OUT(MAX) 30% ripple current at nominal ⎛ • ...
Page 15
... Si4840 1μF PGND + 100k SN PGOOD R S 12mΩ – SN 100k FB GND 100pF Figure 4. Design Example: 2.5V/10A Output LT3740 = ΔI • (ESR) = (10A)(0.005Ω)= 50mV LOAD = 7V, step-up inductor 20V C IN 100μF 35V L1 2.0μH V 2.5V OUT 10A 680μF 4V × ...
Page 16
... LT3740 U U APPLICATIO S I FOR ATIO PC Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. ■ Place the power components close together with short and wide interconnecting trances. The power components consist of the top and bottom MOSFETs, ...
Page 17
... RANGE GND FB 1500pF 22pF Efficiency vs Load Current 15V 20V 3.3V OUT LOAD CURRENT (A) LT3740 20V 20μF 3.4μH V OUT 3.3V 10A D1 B340A 2k 100μF × 3 22pF 255k 80.6k 3740 TA02a 10 3740 TA02b 3740fa 17 ...
Page 18
... LT3740 U TYPICAL APPLICATIO S 22μH 10k 1μF 10k 7.5k 680pF 18 2.5V/10A 1μF LT3740 SWB BGDP BIAS V IN 1Ω M1 TGATE HAT2168H SHDN 1Ω XREF SN 1Ω M2 BGATE HAT2165H – PGND RANGE GND FB 22pF EFFICIENCY 15V 2.5V OUT ...
Page 19
... Plastic DFN (5mm × 3mm) (Reference LTC DWG # 05-08-1706) 0.65 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 4.40 ±0.05 (2 SIDES) 5.00 ±0.10 (2 SIDES 0.20 TYP 1.65 ± 0.10 3.00 ±0.10 (2 SIDES) (2 SIDES) 0.75 ±0.05 0.00 – 0.05 LT3740 R = 0.115 0.40 ± 0.10 TYP 9 16 PIN 1 NOTCH (DHC16) DFN 1103 8 1 0.25 ± 0.05 0.50 BSC 4.40 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 19 3740fa ...
Page 20
... Wide Operating Range LTC3824 High Voltage, Wide Input Range, Step-Down Controller With Low I Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● High Efficiency Step-Down Converter 22μH LT3740 SWB BGDP 1μF BIAS V IN 1Ω M1 TGATE HAT2168H SHDN 1Ω ...