LTC3780 Linear Technology Corporation, LTC3780 Datasheet
LTC3780
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LTC3780 Summary of contents
Page 1
... OUT transfers between operating modes, the LTC3780 is ideal for automotive, telecom and battery-powered systems. The operating mode of the controller is determined through the FCB pin. For boost operation, the FCB mode pin can select among Burst Mode and Forced Continuous mode ...
Page 2
... Peak Output Current <10µs (TG1, TG2, BG1, BG2) ... 3A INTV Peak Output Current ................................ 40mA CC Operating Temperature Range (Note 7) LTC3780E ........................................... – 40°C to 85°C LTC3780I .......................................... – 40°C to 125°C Junction Temperature (Note 2) ............................ 125°C Storage Temperature Range .................. –65°C to 125°C Lead Temperature (Soldering, 10 sec) SSOP Only ........................................................ 300°C CC ...
Page 3
... C = 3300pF (Note 5) LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD LTC3780 MIN TYP MAX UNITS ● 0.1 0.5 % ● –0.1 –0.5 % 0.002 0.02 %/V 0.32 mS 0.6 MHz µA 2400 µ ...
Page 4
... Performance over the –40°C to 85°C operating temperature range is assured by design, characterization and correlation to a specified ITH with statistical process controls. The LTC3780I is guaranteed over the – 40°C to 125°C operating temperature range. MIN TYP MAX ...
Page 5
... INPUT VOLTAGE (V) 3780 G05 EXTV Switch Resistance CC vs Temperature –50 – 100 125 TEMPERATURE (°C) 3780 G08 LTC3780 Efficiency vs Output Current (Buck Operation) 100 CCM 70 DCM 18V 12V OUT 40 0.01 0 (A) ...
Page 6
... LTC3780 W U TYPICAL PERFOR A CE CHARACTERISTICS Continuous Current Mode (CCM 6V 12V) IN OUT SW2 10V/DIV SW1 10V/DIV V OUT 100mV/DIV I L 2A/DIV 3780 G10 5µs/DIV 12V OUT Burst Mode Operation ( 12V) IN OUT SW2 10V/DIV SW1 10V/DIV V OUT 500mV/DIV ...
Page 7
... Valley Current Threshold vs V (Buck) ITH 100 50 0 –50 –100 –150 0 0.8 1.2 1.6 2.0 2.4 0.4 V (V) ITH 3780 G26 LTC3780 Minimum Current Sense Threshold vs Duty Factor (Buck) –20 –40 –60 –80 100 DUTY FACTOR (%) 3780 G21 Minimum Current Sense Threshold vs Temperature 200 BOOST 150 100 ...
Page 8
... LTC3780 W U TYPICAL PERFOR A CE CHARACTERISTICS Load Step V OUT 500mV/DIV I L 5A/DIV 3780 G27 V = 18V 200µs/DIV 12V OUT LOAD STEP CONTINUOUS MODE Line Transient V IN 10V/DIV V OUT 500mV/DIV I L 1A/DIV V = 12V 500µs/DIV OUT LOAD ...
Page 9
... Main Input Supply. Bypass this pin to IN SGND with an RC filter (1Ω, 0.1µF). Exposed Pad (Pin 33, QFN Only): This pin is SGND and must be soldered to PCB ground. to keep the pin within IN LTC3780 and C (Figure 11) connects here. The BOOST2 INTV ...
Page 10
... LTC3780 W BLOCK DIAGRA STBYMD FCB 1.2V 4 1.2µA SS RUN 100k 5.7V – EXTV CC INTV SGND 10 FCB I LIM + BUCK LOGIC – I REV + – FCB BOOST LOGIC I CMP + OV – – + SLOPE EA – + SHDN RUN/ RST SS 4 REF PHASE DET CLK OSCILLATOR 6V LDO REG – ...
Page 11
... Figure 1 shows a simplified diagram of how the four power switches are connected to the inductor, V GND. Figure 2 shows the regions of operation for the LTC3780 as a function of duty cycle D. The power switches are properly controlled so the transfer between modes is continuous. When V region is reached; the mode-to-mode transition time is typically 200ns ...
Page 12
... LTC3780 U OPERATIO and Switch A is turned on for the remainder of the cycle. Switches A and B will alternate, behaving like a typical synchronous buck regulator. The duty cycle of switch A increases until the maximum duty cycle of the converter in Buck mode reaches D , given by: MAX_BUCK D = 100% – D MAX_BUCK ...
Page 13
... DCM with Constant Freq a resistive feedback divider. During buck operation at no load, Switch A is turned on for its minimum on-time. This will not occur every clock cycle when the output load LTC3780 (Figure 13) to recharge. In Buck mode recharge. This is the least ...
Page 14
... LTC3780 U OPERATIO current drops below 1% of the maximum designed load. The body diode of Synchronous Switch B or the Schottky diode, which is in parallel with Switch B, is used to discharge the inductor current; Switch B only turns on every ten clock cycles to allow C B current is applied, Switch A turns on every cycle, and its on-time begins to increase ...
Page 15
... RUN and SS pins, provid- ing an output power source for “wake-up” circuitry. By- pass the pin with a small capacitor (0.1µF) to ground if the pin is not connected potential. LTC3780 pin voltage. The TH 3780fc 15 ...
Page 16
... LTC3780 U U APPLICATIO S I FOR ATIO Figure basic LTC3780 application circuit. External component selection is driven by the load requirement, and begins with the selection of R SENSE value. Next, the power MOSFETs are selected. Finally, C and C are selected. This circuit can be configured for OUT operation input voltage of 36V ...
Page 17
... Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient. Capacitors are now available with low ESR and high ripple 10 current ratings, such as OS-CON and POSCAP. 3780 F08 /V IN OUT LTC3780 V V OUT IN I • • – 1 ...
Page 18
... I RSS The drive voltage is set by the 6V INTV quently, logic-level threshold MOSFETs must be used in LTC3780 applications. If the input voltage is expected to drop below 5V, then the sub-logic threshold MOSFETs should be considered. In order to select the power MOSFETs, the power dissi- pated by the device must be known. For Switch A, the maximum power dissipation happens in Boost mode, when it remains on all the time ...
Page 19
... INTV Regulator CC An internal P-channel low dropout regulator produces 6V at the INTV the drivers and internal circuitry within the LTC3780. The INTV pin regulator can supply a peak current of 40mA CC and must be bypassed to ground with a minimum of 4.7µF tantalum, 10µF special polymer or low ESR type electro- lytic capacitor. A 1µ ...
Page 20
... CC the MOSFET gate drive requirements. Output Voltage The LTC3780 output voltage is set by an external feedback resistive divider carefully placed across the output capaci- tor. The resultant feedback signal is compared with the internal precision 0.800V voltage reference by the error amplifier. The output voltage is given by the equation: ⎛ ...
Page 21
... It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Although all dissipative elements in circuit produce losses, four main sources account for most of the losses in LTC3780 circuits losses. These arise from the resistances of the ...
Page 22
... LTC3780 U U APPLICATIO S I FOR ATIO 3. INTV current. This is the sum of the MOSFET driver CC and control currents. This loss can be reduced by supplying INTV current through the EXTV CC a high efficiency source, such as an output derived boost network or alternate supply if available and C loss ...
Page 23
... Switch A, Switch B and D1 in one compact IN , Switch C, Switch D and D2 in one OUT SW2 SW1 SENSE LTC3780 CKT Figure 10. Switches Layout = OUT C OUT GND 3780 F10 3780fc 23 ...
Page 24
... LTC3780 U U APPLICATIO S I FOR ATIO • Use immediate vias to connect the components (in- cluding the LTC3780’s SGND and PGND pins) to the ground plane. Use several large vias for each power component. • Use planes for V and V to maintain good voltage ...
Page 25
... SGND BG1 8 17 RUN PGND 9 16 FCB BG2 10 15 PLLFLTR SW2 PLLIN TG2 12 13 STBYMD BOOST2 R IN Figure 11. LTC3780 Layout Diagram Figure 12. Sense Lines Layout LTC3780 V OUT C OUT SENSE 3780 F11 PGND ...
Page 26
... LTC3780 PACKAGE DESCRIPTIO 7.8 – 8.2 0.42 ±0.03 RECOMMENDED SOLDER PAD LAYOUT 5.00 – 5.60** (.197 – .221) 0.09 – 0.25 0.55 – 0.95 (.0035 – .010) (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE * DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE ** DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH ...
Page 27
... Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693) 0.70 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC R = 0.05 0.75 ± 0.05 TYP 0.00 – 0.05 3.50 REF (4-SIDES) 0.200 REF LTC3780 BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.30 TYP R = 0.115 OR 0.35 × 45° CHAMFER TYP 31 32 0.40 ± 0. 3.45 ± 0.10 3.45 ± 0.10 (UH32) QFN 0406 REV D 0.25 ± ...
Page 28
... D B 1N5819 PLLIN TG2 13 STBYMD BOOST2 10Ω 100Ω 100Ω Figure 13. LTC3780 12V/5A, Buck-Boost Regulator COMMENTS , 2.5V ≤ SENSE 60V, Drivers 10,000pF Gate Capacitance 550kHz Operation 3.5V ≤ V ≤ 36V, 0.8V ≤ ≤ V ≤ 36V, Fast Transient Response, Current Mode 5.5V ≤ ...