LTC3773 Triple Output Synchronous 3-Phase DC/DC Controller with Up/Down Tracking FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LTC®3773 is a high performance, 3-phase, triple output synchronous step-down switching regulator controller with output voltage power up/down tracking capability. The controller allows for sequential, coincident or ratiometric tracking. Current Mode Controller with Onboard MOSFET Drivers Programmable Power Up/Down Tracking Wide VIN Range: 3.3V to 36V (VCC = 5V) ±1% 0.
LTC3773 ABSOLUTE MAXIMUM RATINGS (Note 1) Topside Driver Voltage (BOOSTn) .............. 42V to –0.3V Switch Voltage (SWn) ................................... 36V to –1V Boosted Driver Voltage (BOOSTn – SWn) .... 7V to –0.3V Supply Voltages (VCC, VDR).......................... 7V to –0.3V PGOOD, PHASEMD, PLLFLTR, PLLIN/FC, SDBn, TRACKn, VFBn ...............................(VCC + 0.3V) to –0.3V SENSE+n, SENSE –n ........................ (1.1 • VCC) to –0.3V ITHn Voltage.....................................
LTC3773 ELECTRICAL CHARACTERISTICS (Note 3) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VDR = VBOOST = VSDB = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS Feedback Voltage VITH = 1.2V, 0°C ≤ T ≤ 85°C (Note 4) MIN TYP MAX UNITS ● 0.594 0.591 0.600 0.600 0.606 0.609 –15 –100 nA ● 65 60 75 75 85 90 mV mV 0.15 –0.2 0.5 –0.5 % % 3.
LTC3773 ELECTRICAL CHARACTERISTICS (Note 3) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VDR = VBOOST = VSDB = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.1 0.
LTC3773 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current, Shutdown CH2 and CH3 Efficiency vs Load Current, Power-Up CH2 and CH3 100 10000 100 1000 60 100 CONTINUOUS MODE 50 40 10 DISCONTINUOUS MODE 30 Burst Mode OPERATION 20 EFFICIENCY POWER LOSS 10 0 0.001 1 0.01 0.1 1 10 80 1000 70 60 CONTINUOUS 100 MODE 50 DISCONTINUOUS MODE 40 30 Burst Mode OPERATION 20 0 0.001 CHANNEL 1 LOAD CURRENT (A) VIN = 12V, VCC = 5V, VOUT1 = 2.5V fSW = 220kHz 3773 G01 1.
LTC3773 TYPICAL PERFORMANCE CHARACTERISTICS IVCC and IVDR vs Load Current IVDR and IVCC vs Switching Frequency IVDR 2.4 60 2.3 40 2.2 20 2.1 0 150 250 450 550 650 350 SWITCHING FREQUENCY (kHz) FORCED CONTINUOUS 2.5 IVCC IVCC (mA) IVDR (mA) VIN = 10V, VCC = VDR = 5V, FORCED CONTINUOUS MODE 100 VOUT1 = 2.5V WITH 5A LOAD VOUT2 = 1.8V WITH 5A LOAD VOUT3 = 1.2V WITH 5A LOAD 80 100 2.6 IVCC + IVDR (mA) 120 DISCONTINUOUS MODE 10 Burst Mode OPERATION 1 0.001 2.
LTC3773 TYPICAL PERFORMANCE CHARACTERISTICS Error Amplifier gm vs Temperature 1.00 3.2 604.5 0.75 3.1 603.0 0.50 601.5 0.25 600.0 0 598.5 –0.25 597.0 –0.50 595.5 –0.75 594.0 –50 –25 25 50 75 0 TEMPERATURE (°C) 100 ERROR AMPLIFIER gm (mmho) 606.0 ΔVFB (%) VFB (mV) VFB vs Temperature 3.0 2.9 2.8 2.7 2.6 2.5 2.4 –1.00 125 2.
LTC3773 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Current Limit Threshold vs VFB 80 SENSE Pin Input Current vs SENSE Common Mode Voltage 40 VTRACK = 1V 70 20 50 ISENSE (μA) VSENSE (mV) 60 40 30 10 0 –10 20 –20 10 0 VCC = 5V ISENSE = ISENSE+ = ISENSE– 30 0 100 200 300 400 VFB (mV) 500 –30 600 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.
LTC3773 TYPICAL PERFORMANCE CHARACTERISTICS VCC Undervoltage Reset Voltage vs Temperature TRACK and SDB Pull-Up Current vs Temperature 1.2 ITRACK 4.3 4.2 PULLUP CURRENT (μA) VCC UNDERVOLTAGE RESET (V) 4.4 POWER UP 4.1 4.0 SHUTDOWN 3.9 0.9 0.6 ISDB2 0.3 3.8 3.7 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 0 –50 125 –25 0 25 50 75 TEMPERATURE (°C) 3773 G24 PLLIN/FC, PHASEMD, PLLFLTR, Threshold Voltage vs Temperature 3.3 170 2.
LTC3773 PIN FUNCTIONS (G/UHF) SENSE1+ (Pin 1/Pin 34): The (+) Input to the Channel 1 Differential Current Comparator. The ITH1 pin voltage and controlled offsets between the SENSE1– and SENSE1+ pins in conjunction with RSENSE set the channel 1 current trip threshold. SENSE1– (Pin 2/Pin 35): The (–) Input to the Channel 1 Differential Current Comparator. SDB/SDB1, SDB2, SDB3 (Pin 3/Pins 36, 37, 38): Shutdown, Active Low. For G package, SDB1, SDB2 and SDB3 are shorted at the SDB pin.
LTC3773 PIN FUNCTIONS (G/UHF) PLLIN/FC (Pin 20/Pin 17): Synchronization Input to the Phase Detector and Forced Continuous Control Input. When floating, it sits around 1.6V, and the controller enters discontinuous mode operation at light load. Shorting this pin low or high for more than 20μs enables Burst Mode operation or forced continuous current mode operation, respectively.
LTC3773 FUNCTIONAL DIAGRAM CLK3 CLK2 OSCILLATOR – + CH1 PBAD 3V DUPLICATE FOR CH2 AND CH3 BOT + – VCC – – + OV I1 EA + + R1 CH3 SHDN VCC CC RC + – 2.4V SDB3 – ++ CH2 SHDN + – 1.8V SDB2 CIN – – + BG BOT PGND VCC I2 3mV 36k 36k 5.3 x VFB 0.645V 54k 1.8V L SENSE+ SENSE– RSENSE COUT 54k 2.4V VOUT CH1 SHDN VDR SHDN DRV + – SLOPE COMP + SLOPE COMP ITH – + VDR SLEEP – CB SW SHDN + DB TG TOP SWITCH LOGIC RS LATCH 0.5V 0.
LTC3773 OPERATION (Refer to the Functional Diagram) Main Control Loop The LTC3773 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 turned off when the main current comparator, I1, resets the RS latch. The peak inductor current at which I1 resets the RS latch is controlled by the voltage on the ITH pin, which is the output of the error amplifier EA.
LTC3773 OPERATION (Refer to the Functional Diagram) as a Burst Mode switching regulator. Burst Mode operation clamps the minimum peak inductor current to approximately 20% of the current limit programmed by RSENSE. As the load current goes down, the EA will reduce the voltage on the ITH pin. When the ITH voltage drops below 0.5V, the internal SLEEP signal goes high and both external MOSFETs are turned off. In Burst Mode operation, the load current is supplied by the output capacitor.
LTC3773 APPLICATIONS INFORMATION The basic application circuit is shown on the first page of this data sheet. External component selection is driven by the load requirement, and normally begins with the selection of an inductance value based upon the desired operating frequency, inductor current and output voltage ripple requirements. Once the inductors and operating frequency have been chosen, the current sensing resistors can be calculated. Next, the power MOSFETs and Schottky diodes are selected.
LTC3773 APPLICATIONS INFORMATION mainly depends on the price vs size requirements and any radiated field/EMI requirements. New designs for high current surface mount inductors are available from numerous manufacturers, including Coiltronics, Vishay, TDK, Pulse, Panasonic, Vitec, Coilcraft, Toko and Sumida.
LTC3773 APPLICATIONS INFORMATION where δ is the temperature dependency of RDS(ON), RDR is the effective top driver resistance (approximately 2Ω at VGS = VMILLER), and VIN is the drain potential and the change in drain potential in the particular application. VTH(IL) is the typical gate threshold voltage shown in the power MOSFET data sheet at the specified drain current. CMILLER is the calculated capacitance using the gate charge curve from the MOSFET data sheet and the technique described above.
LTC3773 APPLICATIONS INFORMATION This formula has a maximum value at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that capacitor manufacturer’s ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor, or to choose a capacitor rated at a higher temperature than required.
LTC3773 APPLICATIONS INFORMATION age output current IMAX equal to the peak value less half the peak-to-peak ripple current, ΔIL. Allowing a margin for variations in the IC and external component values yields: 55mV RSENSE = IMAX VIN RZ 2k + CIN 100Ω Q1 DB BOOST CB VOUT VZ 6.8V COUT The IC works well with values of RSENSE from 0.002Ω to 0.1Ω.
LTC3773 APPLICATIONS INFORMATION SENSE+/SENSE– Pins The common mode input range of the current comparator sense pins is from 0V to (1.1)VCC. Continuous linear operation is guaranteed throughout this range allowing output voltage setting from 0.6V to 7.7V, depending upon the voltage applied to VCC. A differential NPN input stage is biased with internal resistors from an internal 2.4V source as shown in Figure 1.
LTC3773 APPLICATIONS INFORMATION An internal 1μA current source pull-up at the TRACK pin programs the output to take about 600ms/μF to reach its steady state value. The output voltage ramp down slew rate can be controlled by the external capacitor CSLEW and the TRACK DOWN switch as shown in Figure 5a and 5b. With a simple configuration, TRACK allows VOUT startup to track the master channel as shown qualitatively in Figures 5a and 5b.
LTC3773 APPLICATIONS INFORMATION add an extra tracking resistive divider. When the tracking resistive divider input is grounded, the pull-up current flowing through the network could produce a small unwanted offset at the TRACK pin, forcing the controller to create an unwanted low voltage supply at the regulator output. To compensate for this error, the LTC3773 introduces a 30mV offset in the tracking circuit, which disables the driver until the potential at the TRACK pin is above 30mV.
LTC3773 MOSFET of controller 1 to be locked to the rising edge of an external clock signal applied to the PLLIN/FC pin. The turn-on of controller 2’s/3’s external N-channel MOSFET and CLKOUT signal are controlled by the PHASEMD pin as showed in Table 1. Note that when PHASEMD is forced high, controller 2 and controller 3 outputs can be connected in parallel to produce a higher output power voltage source. Table 1.
LTC3773 APPLICATIONS INFORMATION The LTC3773 can be configured to operate at any switching frequency within the synchronization range. Figure 7 shows a simple circuit to achieve this. The resistive divider at the PLLFLTR pin programs the LTC3773 switching frequency according to the transfer curve of Figure 6b. By connecting the PLLIN/FC pin to the BG1 or the CLKOUT (UHF package only) node, the pre-set frequency selection is disengaged and the PLLFLTR pin potential determines the switching frequency.
LTC3773 APPLICATIONS INFORMATION The ITH series RC-CC filter sets the dominant pole-zero loop compensation. The values can be modified slightly to maximize transient response once the final PC layout is done and the particular output capacitor type and value have been determined. The output capacitors need to be decided upon because the various types and values determine the loop feedback factor gain and phase.
LTC3773 APPLICATIONS INFORMATION that the minimum on-time of 130ns is not violated. The minimum on-time occurs at maximum VIN: VOUT 1.8V tON(MIN) = = = 372ns VIN(MAX)f 22V(220kHz) The RSENSE resistor value can be calculated by using the maximum current sense voltage specification with a conservative maximum sense current threshold of 55mV: RSENSE 55mV 3.2m 17.3A Use a commonly available 0.003Ω sense resistor. Since the output voltage is below 2.
LTC3773 APPLICATIONS INFORMATION nected between the (+) terminal of COUT and SGND and a small decoupling capacitor should be placed across this divider; as close as possible to the LTC3773 SGND pin and away from any high current or high frequency switching nodes. 5. Are the SENSE– and SENSE+ printed circuit traces for each channel routed together with minimum PC trace spacing? The filter capacitors between SENSE+ and SENSE– for each channel should be as close as possible to the pins of the IC.
LTC3773 APPLICATIONS INFORMATION SW1 L1 VOUT1 RSENSE1 COUT1 D1 SW2 VIN RIN L2 + BOLD LINES INDICATE HIGH SWITCHING CURRENTS. KEEP LINES TO A MINIMUM LENGTH. COUT2 D2 SW3 L3 + RL2 VOUT3 RSENSE3 D3 RL1 VOUT2 RSENSE2 CIN + COUT3 + RL3 3773 F10 Figure 10.
LTC3773 APPLICATIONS INFORMATION 10Ω 10Ω POWER DOWN VOUT1 1nF POWER DOWN VOUT2 47.5k 2 3 5 6 7 8 9 10 20k VOUT2 10k PGOOD PHASEMD SDB1 ITH2 TG2 ITH3 BOOST2 VFB2 BOOST3 VFB3 TG3 TRACK2 SW3 TRACK3 BG1 11 SENSE2– BG2 12 SENSE2+ VDR SENSE3 – 10k SW2 LTC3773 13 14 15 16 17 18 31 30 0.1μF 29 HAT2168H 27 26 + CIN 56μF 25V x5 L1 1μH 3mΩ B340B 0.1μF CMDSH-3 HAT2165H VIN 25 24 VIN 4.5V TO 22V + 28 0.1μF CMDSH-3 HAT2168H HAT2165H L2 0.6μH VOUT1 2.
LTC3773 PACKAGE DESCRIPTION G Package 36-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 12.50 – 13.10* (.492 – .516) 1.25 ±0.12 7.8 – 8.2 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 5.3 – 5.7 7.40 – 8.20 (.291 – .323) 0.42 ±0.03 0.65 BSC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 RECOMMENDED SOLDER PAD LAYOUT 2.0 (.079) MAX 5.00 – 5.60** (.197 – .221) 0° – 8° 0.09 – 0.25 (.0035 – .010) 0.55 – 0.95 (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2.
LTC3773 PACKAGE DESCRIPTION UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701) 0.70 ± 0.05 5.50 ± 0.05 (2 SIDES) 4.10 ± 0.05 (2 SIDES) 3.15 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 5.15 ± 0.05 (2 SIDES) 6.10 ± 0.05 (2 SIDES) 7.50 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD LAYOUT 5.00 ± 0.10 (2 SIDES) 3.15 ± 0.10 (2 SIDES) 0.75 ± 0.05 0.00 – 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 37 38 0.40 ±0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.
LTC3773 TYPICAL APPLICATION POWER DOWN VOUT1 POWER DOWN VOUT2 10Ω POWER DOWN VOUT3 1000pF 150pF 5 150pF 6 10k 7 10k 8 0.01μF 9 0.01μF 10 11 12 20k TG2 LTC3773 ITH3 BOOST2 VFB2 BOOST3 VFB3 TG3 TRACK2 SW3 TRACK3 BG1 SENSE2– SENSE2+ 14 15 16 17 18 BG2 VDR 31 30 1 0.1μF 5 29 + 1000pF 27 26 2, 3 0.1μF CMDSH-3 25 CMDSH-3 24 0.1μF 8 Si4816BDY 1 23 5 22 4 6, 7 19 + 8 Si4816BDY 1 0.1μF 6, 7 22μF X5R 7mΩ VOUT2 2.5V/5A + COUT2 220μF 4V 22μF X5R VIN 4.
