LTC3785 LINER [Linear Technology], LTC3785 Datasheet
LTC3785
Available stocks
Related parts for LTC3785
LTC3785 Summary of contents
Page 1
FeaTures Single Inductor Architecture Allows V n Below or Equal to Regulated V OUT Programmable Input or Output Current Feedback Loop n Wide V Range 38V Output Voltage Accuracy: 0.8V < Synchronous Rectification: ...
Page 2
LTC3789 absoluTe MaxiMuM raTings Input Supply Voltage (V ) ......................... 40V to –0.3V IN Topside Driver Voltages (BOOST1, BOOST2) .................................. 46V to –0.3V Switch Voltage (SW1, SW2) ......................... 40V to –5V + Current Sense Voltages ( OSENSE OSENSE ...
Page 3
T SYMBOL PARAMETER V Input Supply Voltage IN V Output Voltage OUT V Regulated Feedback Voltage FB I Feedback Current FB V Reference Voltage Line Regulation REFLNREG V Output Voltage Load ...
Page 4
LTC3789 elecTrical characTerisTics junction temperature range, otherwise specifications are at T SYMBOL PARAMETER INTV Linear Regulator CC V Internal V Voltage INTVCCVIN CC V INTV Load Regulation LDOVIN CC V Internal V Voltage INTVCCEXT CC V INTV Load Regulation LDOEXT ...
Page 5
Typical perForMance characTerisTics Efficiency vs Output Current (Boost Region) 100 12V OUT DCM DCM 10 CIRCUIT OF FIGURE 13 FCM FCM 0 10 100 1000 10000 ...
Page 6
LTC3789 Typical perForMance characTerisTics Forced Continuous Mode SW1 10V/DIV SW2 10V/DIV I L 1A/DIV 3789 G10 4µs/DIV 12V OUT Pulse-Skipping Mode SW1 10V/DIV SW2 10V/DIV I L 1A/DIV 3789 G13 4µs/DIV ...
Page 7
Typical perForMance characTerisTics Maximum Current Sense Threshold vs Duty Factor (Boost) 150 140 130 120 110 100 DUTY FACTOR (%) Peak Current Threshold vs V (Boost) ITH 200 150 100 ...
Page 8
LTC3789 Typical perForMance characTerisTics Line Transient V ITH V IN 30V (AC) OUT 500mV/DIV I L 2A/DIV 1ms/DIV pin FuncTions (SSOP/QFN) V (Pin 1/Pin 26): Error Amplifier Feedback Pin. Receives FB the feedback voltage for the controller ...
Page 9
FuncTions (SSOP/QFN) V (Pin 11/Pin 8): V Sense Input to the Buck- OUTSNS OUT Boost Transition Comparator. Connect this pin to the drain of the top N-channel MOSFET on the output side. I (Pin 12/Pin 9): Input/Output Average Current ...
Page 10
LTC3789 block DiagraM CHARGE BOOST1 PUMP CHARGE BOOST2 PUMP V FLD 1.2µA RUN SHDN MODE/ PLLIN F PHASE DET IN 220k 10µA FREQ OSCILLATOR 4.8V EXTV CC – INTV 5. SGND 10 FCB ...
Page 11
MAIN CONTROL LOOP The LTC3789 is a current mode controller that provides an output voltage above, equal to or below the input voltage. The LTC proprietary topology and control architecture employs a current-sensing resistor. The inductor current is controlled ...
Page 12
LTC3789 operaTion POWER SWITCH CONTROL Figure 1 shows a simplified diagram of how the four power switches are connected to the inductor, V and GND. Figure 2 shows the regions of operation for the LTC3789 as a function of duty ...
Page 13
The duty cycle of switch C decreases until the minimum duty cycle of the converter reaches D • 100% = 8.33% MIN _ BOOST 12 Figure 5 shows typical boost ...
Page 14
LTC3789 operaTion Constant-Current Regulation The LTC3789 provides a constant-current regulation loop for either input or output current. A sensing resistor close to the input or output capacitor will sense the input or output current. When the current exceeds the programmed ...
Page 15
The Typical Application on the first page is a basic LTC3789 application circuit. External component selec- tion is driven by the load requirement, and begins with the selection of R and the inductor value. Next, the SENSE power ...
Page 16
LTC3789 applicaTions inForMaTion With the typical 100Ω resistors shown here, the value of capacitor C should be 1µF to 2.2µF . The current loop’s F transfer function should approximate that of the voltage loop. Crossover frequency should be one-tenth the ...
Page 17
LTC3789’s internal VCO. This is guaranteed to be between 200kHz and 600kHz. A simplified block diagram is shown in Figure 10. 2.4V MODE/ DIGITAL PLLIN SYNC PHASE/ EXTERNAL OSCILLATOR FREQUENCY ...
Page 18
LTC3789 applicaTions inForMaTion In the boost region, the discontinuous current shifts from the input to the output reducing the output voltage ripple. The effects of ESR (equivalent series resistance) and the bulk capacitance must be considered when ...
Page 19
C is usually specified by the MOSFET manufactur- RSS ers. The constant k, which accounts for the loss caused by reverse recovery current, is inversely proportional to the gate drive current and has an empirical value of ...
Page 20
LTC3789 applicaTions inForMaTion Significant efficiency and thermal gains can be realized by powering INTV from the output, since the V CC resulting from the driver and control currents will be scaled by a factor of (Duty Cycle)/(Switcher Efficiency). Tying the ...
Page 21
The soft-start range is defined to be the voltage range from 0V to 0.8V on the SS pin. The total soft-start time can be calculated as 0.8 • SOFTSTART 3µA Regardless of ...
Page 22
LTC3789 applicaTions inForMaTion Design Example 18V 12V OUT OUT(MAX 400kHz Maximum ambient temperature = 60°C Set the frequency at 400kHz by applying 1.2V on the FREQ pin (see ...
Page 23
The Vishay SiR422DP has a typical 125°C and V = 4.5V The maximum dissipation in QB occurs at maximum input voltage when the circuit is operating in the buck region. The dissipation is: ...
Page 24
LTC3789 applicaTions inForMaTion • Use planes for V and V to maintain good voltage IN OUT filtering and to keep power losses low. • Flood all unused areas on all layers with copper. Flooding with copper will reduce the temperature ...
Page 25
R1 R2 20k 280k V OUT 6.8nF PGOOD 1000pF 3 SENSE 3300pF SENSE 68k SGND 7 MODE/PLLIN 121k 8 FREQ ...
Page 26
LTC3789 package DescripTion .254 MIN .0165 .0015 RECOMMENDED SOLDER PAD LAYOUT .0075 – .0098 (0.19 – 0.25) .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES 2. DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE 26 GN Package ...
Page 27
DescripTion 4.50 ± 0.05 3.10 ± 0.05 2.50 REF 2.65 ± 0.05 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 TOP MARK (NOTE 6) 5.00 ± ...
Page 28
... V IN L1: WÜRTH 7443630550 relaTeD parTs PART NUMBER DESCRIPTION LTC3780 High Efficiency (Up to 98%) Synchronous, 4-Switch Buck-Boost DC/DC Controller LTC3785 High Efficiency (Up to 98%) Synchronous, 4-Switch Buck-Boost DC/DC Controller LTM4605 High Efficiency Buck-Boost DC/DC µModule™ LTM4607 High Efficiency Buck-Boost DC/DC µModule LTM4609 High Efficiency Buck-Boost DC/DC µModule ...