LTC3731CUH#TR Linear Technology, LTC3731CUH#TR Datasheet

Page 1

... MOSFETs and the load. Current foldback provides protection for the external MOSFETs under short-circuit or overload conditions. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode, OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology Corporation. Stage Shedding is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners ...

Page 2

LTC3731 ABSOLUTE AXI U RATI GS Topside Driver Voltages (BOOST ) ............ 38V to –0.3V N Switch Voltage (SW )................................... 32V to –5V N Boosted Driver Voltage (BOOST – Peak Output Current <1ms (TG , ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER V Maximum Current Sense Threshold SENSEMAX I Maximum Current Threshold Match MATCH V Output Voltage Load Regulation LOADREG V Output Voltage Line Regulation REFLNREG g Transconductance Amplifier g m ...

Page 4

LTC3731 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER Power Good Output Indication V PGOOD Voltage Output Low PGL I PGOOD Output Leakage PGOOD I PGOOD/PHASMD Bias I PGOOD PGOOD Trip Thresholds V V Ramping Negative PGTHNEG ...

Page 5

CTIO S BG1 to BG3: High Current Gate Drives for Bottom N-Channel MOSFETs. Voltage swing at these pins is from ground to V BOOST1 to BOOST3: Positive Supply Pins to the Topside Floating Drivers. Bootstrapped ...

Page 6

LTC3731 W U TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs I (Figure 14) OUT 100 V = OPEN 90 FCB FCB FCB ...

Page 7

W U TYPICAL PERFOR A CE CHARACTERISTICS Short-Circuit Arming and Latchoff vs Temperature 5 ARMING 4 LATCHOFF –50 – 100 125 TEMPERATURE (°C) 3731 G10 Maximum SENSE RUN/SS 80 ...

Page 8

LTC3731 W U TYPICAL PERFOR A CE CHARACTERISTICS Shed Mode at 1 Amp, Light Load Current (Circuit of Figure 14) V OUT AC, 20mV/DIV V SW1 10V/DIV V SW2 10V/DIV V SW3 10V/DIV V = 12V 4µs/DIV ...

Page 9

CTIO AL DIAGRA PLLIN PHASE DET F IN 50k PLLFLTR CLKOUT CLK1 CLK2 OSCILLATOR PHASMD** CLK3 PGOOD** – 0.66V + 100µs EAIN DELAY – PROTECTION + 0.54V FCB + FCB – 0.6V – ...

Page 10

LTC3731 U OPERATIO (Refer to Functional Diagram) Main Control Loop The IC uses a constant frequency, current mode step- down architecture. During normal operation, each top MOSFET is turned on each cycle when the oscillator sets the RS latch, and ...

Page 11

U OPERATIO (Refer to Functional Diagram) C) Continuous Current Operation Tying the FCB pin to ground will force continuous current operation. This is the least efficient operating mode, but may be desirable in certain applications. The output can source or ...

Page 12

LTC3731 U OPERATIO (Refer to Functional Diagram) the RUN/SS pin voltage is recycled. This built-in latchoff can be overridden by providing >5µ compliance of 3.8V to the RUN/SS pin. This additional current shortens the soft-start period but prevents ...

Page 13

U U APPLICATIO S I FOR ATIO current and low current operation must also be consid- ered. The PolyPhase approach reduces both input and output ripple currents while optimizing individual output stages to run at a lower fundamental frequency, enhancing ...

Page 14

LTC3731 U U APPLICATIO S I FOR ATIO Power MOSFET and D1, D2, D3 Selection At least two external power MOSFETs must be selected for each of the three output sections: One N-channel MOSFET for the top (main) switch and ...

Page 15

U U APPLICATIO S I FOR ATIO where N is the number of output stages, δ is the tempera- ture dependency the effective top driver DS(ON) DR resistance (approximately 2Ω drain potential ...

Page 16

LTC3731 U U APPLICATIO S I FOR ATIO size or height requirements in the design. Always consult the capacitor manufacturer if there is any question. The Figure 6 graph shows that the peak RMS input current is reduced linearly, inversely ...

Page 17

U U APPLICATIO S I FOR ATIO special polymer capacitors available in case heights ranging from 2mm to 4mm. Other capacitor types in- clude Sanyo POSCAP, Sanyo OS-CON, Nichicon PL series and Sprague 595D series. Consult the manufac- turers for ...

Page 18

LTC3731 U U APPLICATIO S I FOR ATIO Soft-Start/Run Function The RUN/SS pin provides three functions: 1) ON/OFF, 2) soft-start and 3) a defeatable short-circuit latch off timer. Soft-start reduces the input power sources’ surge currents by gradually increasing the ...

Page 19

U U APPLICATIO S I FOR ATIO The value of the soft-start capacitor C scaled with output current, output capacitance and load current characteristics. The minimum soft-start capaci- tance is given by: –4 C > (C )(V ) (10 ) ...

Page 20

LTC3731 U U APPLICATIO S I FOR ATIO PHASE 2.4V DETECTOR/ OSCILLATOR EXTERNAL OSC OSC PLLIN DIGITAL PHASE/ FREQUENCY DETECTOR 50k Figure 9. Phase-Locked Loop Block Diagram PLLFLTR pin is adjusted until the phase and frequency of the external and ...

Page 21

U U APPLICATIO S I FOR ATIO time, V can be monitored for excessive overshoot or OUT ringing, which would indicate a stability problem. The availability of the I pin not only allows optimization of TH control loop behavior, but ...

Page 22

LTC3731 U U APPLICATIO S I FOR ATIO LTC3731 Figure 10. Automotive Application Protection converter. Although the IC has a maximum input voltage of 32V on the SW pins, most applications will be limited to 30V ...

Page 23

U U APPLICATIO S I FOR ATIO which is less than one third of the normal, full load conditions. Incidentally, since the load no longer dissi- pates any power, total system power is decreased by over 90%. Therefore, the system ...

Page 24

LTC3731 U U APPLICATIO S I FOR ATIO 1) Are the signal and power ground paths isolated? Keep the SGND at one end of a printed circuit path thus preventing MOSFET currents from traveling under the IC. The IC signal ...

Page 25

U U APPLICATIO S I FOR ATIO Simplified Visual Explanation of How a 3-Phase Controller Reduces Both Input and Output RMS Ripple Current The effect of multiphase power supply design significantly reduces the amount of ripple current in both the ...

Page 26

LTC3731 U U APPLICATIO S I FOR ATIO The ripple frequency is also increased by three, further reducing the required output capacitance when V as illustrated in Figure 6. The addition of more phases, by phase locking additional controllers, always ...

Page 27

PACKAGE DESCRIPTIO This totals 8V, 2.25W 20V. IN Total of all three synchronous MOSFETs’ AC gate loss ...

Page 28

LTC3731 U TYPICAL APPLICATIO 1µF OPTIONAL FILTER FOR SYNCHRONIZATION 1000pF SYNC IN 0.01µF PLLIN 300kHz 10k 3 PLLFLTR 4 FCB 5 100pF IN 300pF 6 IN 6.04k 9.09k 7 DIFFOUT 8 EAIN 9 SGND ...

Page 29

U TYPICAL APPLICATIO V CC CLKOUT 8.2k 3. OUTS 220pF – V OUTS 4.7k 15k DIFFOUT 330pF EAIN 10Ω× 1000pF – 1000pF – S2 – S3 1000pF + 0.1µF S3 RUN/SS 357k V ...

Page 30

LTC3731 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 ...

Page 31

... SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights Package 32-Lead Plastic QFN (5mm × ...

Page 32

... Optional R Current Mode Synchronous Step-Down SENSE Controller LTC3832 Low V High Power Synchronous Controller IN LTC4008 4A Multichemistry Multicell Battery Charger trademark of Linear Technology Corporation. SENSE Linear Technology Corporation 32 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● COMMENTS Reduces C IN 3.5V ≤ V ≤ ...