LTC3728 Linear Technology, LTC3728 Datasheet
LTC3728
Available stocks
Related parts for LTC3728
LTC3728 Summary of contents
Page 1
... MOSFET until V can select among Burst Mode, constant frequency mode and continuous inductor current mode or regulate a secondary winding. The LTC3728 includes a power good output pin that indicates when both outputs are within 7.5% of their designed set point. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ...
Page 2
... V = 3.6V to 30V (Note 3) IN (Note 3) Measured in Servo Loop; ∆I Voltage = 1.2V to 0.7V TH Measured in Servo Loop; ∆I Voltage = 1.2V to 2.0V TH www.DataSheet4U.com Voltages ...2.7V to – 0.3V OSENSE1 OSENSE2 ORDER PART TOP VIEW NUMBER LTC3728EUH 24 BOOST1 BG1 22 EXTV INTV CC 19 PGND UH PART 18 BG2 ...
Page 3
... CC EXTVCC I = 20mA EXTVCC I = 20mA, EXTV Ramping Positive 1.2V PLLFLTR PLLFLTR ≥ 2.4V V PLLFLTR f < f PLLIN OSC f > f PLLIN OSC LTC3728 www.DataSheet4U.com = 5V unless otherwise noted. MIN TYP MAX 1 450 OUT1 20 ● 0.76 0.800 – 0.50 – 0.18 4.3 ● 3.5 ● 0.84 0. – 85 – 99.4 ...
Page 4
... LTC3728 Note 3: The LTC3728 is tested in a feedback loop that servos V specified voltage and measures the resultant V Note 4: Dynamic supply current is higher due to the gate charge being W U TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Output Current and Mode (Figure 13) ...
Page 5
... Duty Factor DUTY FACTOR (%) Maximum Current Sense Threshold vs Sense Common Mode Voltage COMMON MODE VOLTAGE (V) LTC3728 www.DataSheet4U.com INTV and EXTV Switch CC CC Voltage vs Temperature 5.05 INTV VOLTAGE CC 5.00 4.95 4.90 4.85 4.80 EXTV SWITCHOVER THRESHOLD CC 4.75 4. – 50 – 25 ...
Page 6
... LTC3728 W U TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation 0.0 FCB = 15V IN –0.1 –0.2 –0.3 –0 LOAD CURRENT (A) 3728 G13 Maximum Current Sense Threshold vs Temperature –50 – 100 125 TEMPERATURE (°C) 3728 G17 Soft-Start Up (Figure 13) ...
Page 7
... TEMPERATURE (°C) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0 100 125 –50 3728 G29 LTC3728 www.DataSheet4U.com Constant Frequency (Burst Inhibit) Operation (Figure 13) V OUT 20mV/DIV I L 0.5A/DIV V = 15V 2µs/DIV 3728 G23 OUT PLLFLTR FCB I = 20mA OUT ...
Page 8
... LTC3728 CTIO S G Package/UH Package RUN/SS1, RUN/SS2 (Pins 1, 15/Pins 28, 13): Combina- tion of soft-start, run control inputs and short-circuit detec- tion timers. A capacitor to ground at each of these pins sets the ramp time to full output current. Forcing either of these pins back below 1.0V causes the IC to shut down the circuitry required for that particular controller ...
Page 9
... U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC3728 uses a constant frequency, current mode step-down architecture with the two controller channels operating 180 degrees out of phase. During normal opera- tion, each top MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the main current comparator resets the RS latch ...
Page 10
... I SS gradually released allowing normal, full-current opera- tion. When both RUN/SS1 and RUN/SS2 are low, all LTC3728 controller functions are shut down, including the 5V and 3.3V regulators. Low Current Operation The FCB pin is a multifunction pin providing two func- ...
Page 11
... THEORY AND BENEFITS OF 2-PHASE OPERATION The LTC1628 and the LTC3728 dual high efficiency DC/DC controllers bring the considerable benefits of 2-phase operation to portable applications for the first time. Note- ...
Page 12
... LTC3728 U OPERATIO (Refer to Functional Diagram 2.53A IN(MEAS) (a) Figure 3. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for Dual Switching Regulators Converting 12V to 5V and 3. Each. The Reduced Input Ripple with the LTC1628 2-Phase Regulator Allows Less Expensive Input Capacitors, Reduces Shielding Requirements for EMI and Improves Efficiency ...
Page 13
... U U APPLICATIO S I FOR ATIO Figure 1 on the first page is a basic LTC3728 application circuit. External component selection is driven by the load requirement, and begins with the selection of R and the inductor value. Next, the power MOSFETs and D1 are selected. Finally, C and C ...
Page 14
... Selection criteria for the power MOSFETs include the “ON” resistance R input voltage and maximum output current. When the LTC3728 is operating in continuous mode the duty cycles for the top and bottom MOSFETs are given by: Main Switch Duty Cycle Synchronous Switch Duty Cycle ...
Page 15
... This makes it advisable to further derate the capacitor choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. Always consult the manufacturer if there is any question. LTC3728 − V ...
Page 16
... LTC3728 U U APPLICATIO S I FOR ATIO The benefit of the LTC3728 multiphase can be calculated by using the equation above for the higher power control- ler and then calculating the loss that would have resulted if both controller channels switch on at the same time. The ...
Page 17
... An internal P-channel low dropout regulator produces 5V at the INTV pin from the V supply pin. INTV CC IN the drivers and internal circuitry within the LTC3728. The INTV pin regulator can supply a peak current of 50mA CC and must be bypassed to ground with a minimum of 4.7µF tantalum, 10µF special polymer, or low ESR type electrolytic capacitor. A 1µ ...
Page 18
... If there is no change in input current, then there is no change in efficiency. Output Voltage The LTC3728 output voltages are each set by an external feedback resistive divider carefully placed across the output capacitor. The resultant feedback signal is V ...
Page 19
... IRAMP SS µ pulling both RUN/SS pins below 1V, the LTC3728 is put into low current shutdown (I Q pins can be driven directly from logic as shown in Figure 7. Diode D1 in Figure 7 reduces the start delay but allows C to ramp up slowly providing the soft-start function. ...
Page 20
... Under short-circuit conditions with very low duty cycles, the LTC3728 will begin cycle skipping in order to limit the short-circuit current. In this situation the bottom MOSFET will be dissipating most of the power but less than in normal operation ...
Page 21
... W U Minimum On-Time Considerations Minimum on-time t that the LTC3728 is capable of turning on the top MOSFET determined by internal timing delays and the gate charge required to turn on the top MOSFET. Low duty cycle C: applications may approach this minimum on-time limit and care should be taken to ensure that ...
Page 22
... L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3728 circuits: 1) LTC3728 V cluding loading on the 3.3V internal regulator), 2) INTV regulator current transition losses. ...
Page 23
... CC current of 20mΩ to 50mΩ of ESR. The LTC3728 2-phase architec- IN ture typically halves this input capacitance requirement over competing solutions. Other losses including Schottky conduction losses during dead-time and inductor core losses generally account for less than 2% total additional loss ...
Page 24
... Note that the transient suppressor should not conduct during double-battery operation, but must still clamp the input voltage below breakdown of the converter. Although the LTC3728 has a maximum input voltage of 36V, most applications will be limited to 30V by the MOSFET BVDSS regulator can OUT www ...
Page 25
... ESR of 0.02Ω for low output ripple. The output ripple in continuous mode will be highest at the maximum input voltage. The output voltage ripple due to ESR is approximately: V ORIPPLE 32 k LTC3728 0.042Ω 100pF. At maximum input RSS ...
Page 26
... Are the signal and power grounds kept separate? The combined LTC3728 signal ground pin and the ground return of C terminals. The path formed by the top N-channel MOSFET, Schottky diode and the C leads and PC trace lengths. The output capacitor (–) terminals should be connected as close as possible to the (– ...
Page 27
... All of these nodes have very large and fast moving signals and therefore should be kept on the “output side” of the LTC3728 and occupy minimum PC trace area. LTC3728 www.DataSheet4U.com R ...
Page 28
... LTC3728 U U APPLICATIO S I FOR ATIO 7. Use a modified “star ground” technique: a low imped- ance, large copper area central grounding point on the same side of the PC board as the input and output capacitors with tie-ins for the bottom of the INTV decoupling capacitor, the bottom of the voltage feedback resistive divider and the SGND pin of the IC ...
Page 29
... 28V 5V, 3A/3.3V, 5A/12V, 120mA OUT SWITCHING FREQUENCY = 250kHz MI, M2, M3, M4: NDS8410A L1: SUMIDA CEP123-6R3MC T1: 10µH 1:1.8 — DALE LPE6562-A262 GAPPED E-CORE OR BH ELECTRONICS #501-0657 GAPPED TOROID Figure 12. LTC3728 High Efficiency Low Noise 5V/3A, 3.3V/5A, 12V/120mA Regulator 1M 100k MBRS1100T3 V PULL-UP (<7V) 28 PGOOD PGOOD 27 TG1 ...
Page 30
... V OSENSE2 20k 1% 13 SENSE2 63.4k 1000pF 14 1% 27pF SENSE2 0.1µ 5.2V TO 28V SWITCHING FREQUENCY = 250kHz TO 550kHz 5V, 4A/3.3V, 4A MI, M2: FDS6982S OUT Figure 13. LTC3728 5V/4A, 3.3V/4A Regulator with External Frequency Synchronization 30 V PULL-UP (<7V) 28 PGOOD PGOOD 27 + TG1 26 – SW1 0.1µF 25 BOOST1 BG1 22 ...
Page 31
... UH32 Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693) 0.57 ±0.05 PACKAGE OUTLINE 0.23 ± 0.05 0.50 BSC 0.75 ± 0.05 0.00 – 0.05 3.45 ± 0.10 (4-SIDES) 0.200 REF LTC3728 www.DataSheet4U.com 10.07 – 10.33* (0.397 – 0.407 7.65 – 7.90 (0.301 – 0.311) ...
Page 32
... OPEN PHASMD TG1 180° TG2 U1 LTC3729 90° CLKOUT 90° TG1 270° TG2 U2 LTC3728 90° PLLIN RELATED PARTS PART NUMBER DESCRIPTION LTC1530 High Power Step-Down Synchronous DC/DC Controller in SO-8 LTC1628/LTC1628-PG/ 2-Phase, Dual Output Synchronous Step-Down LTC1628-SYNC DC/DC Controller LTC1629/ 20A to 200A PolyPhase LTC1629-PG ...