LTC3859 Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller DESCRIPTION FEATURES n n n n n n n n n n n n n n n Dual Buck Plus Single Boost Synchronous Controllers Outputs Remain in Regulation Through Cold Crank Down to 2.5V Low Operating IQ: 55μA (One Channel On) Wide Bias Input Voltage Range: 4.5V to 38V Buck Output Voltage Range: 0.
LTC3859 ABSOLUTE MAXIMUM RATINGS (Notes 1, 3) Bias Input Supply Voltage (VBIAS) .............. –0.3V to 40V Buck Top Side Driver Voltages (BOOST1, BOOST2) ............................. –0.3V to 46V Boost Top Side Driver Voltages (BOOST3) ............................................ –0.3V to 76V Buck Switch Voltage (SW1, SW2) ................ –5V to 40V Boost Switch Voltage (SW3) ........................ –5V to 70V INTVCC, (BOOST1–SW1), (BOOST2–SW2), (BOOST3–SW3),.......... –0.3V to 6V RUN1, RUN2, RUN3 ...
LTC3859 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3859EFE#PBF LTC3859EFE#TRPBF LTC3859FE 38-Lead Plastic TSSOP –40°C to 125°C LTC3859IFE#PBF LTC3859IFE#TRPBF LTC3859FE 38-Lead Plastic TSSOP –40°C to 125°C LTC3859EUHF#PBF LTC3859EUHF#TRPBF 3859 38-Lead (5mm ¥ 7mm) Plastic QFN –40°C to 125°C LTC3859IUHF#PBF LTC3859IUHF#TRPBF 3859 38-Lead (5mm ¥ 7mm) Plastic QFN –40°C to 125°C Consult LTC Marketing for parts specified with wi
LTC3859 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VBIAS = 12V, VRUN1,2,3 = 5V, EXTVCC = 0V unless otherwise noted.
LTC3859 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VBIAS = 12V, VRUN1,2,3 = 5V, EXTVCC = 0V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 5.0 5.4 5.6 V 0.7 2 % 5.4 5.6 V 0.
LTC3859 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3859 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3859E is guaranteed to meet specifications from 0°C to 85°C junction temperature.
LTC3859 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency and Power Loss vs Output Current (Buck) 100 Efficiency vs Output Current (Buck) 100 50 CCM EFFICIENCY 10 PULSE-SKIPPING 30 EFFICIENCY BURST LOSS 20 BURST EFFICIENCY 1 CCM LOSS 10 PULSE-SKIPPING LOSS 0.1 0 0.0001 0.001 0.1 0.01 1 10 OUTPUT CURRENT (A) 3859 G01 FIGURE 12 CIRCUIT VIN = 10V, VOUT = 5V 40 98 70 60 50 40 97 96 95 30 94 20 93 10 FIGURE 12 CIRCUIT 0 0.0001 0.001 0.1 0.
LTC3859 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency and Power Loss vs Output Current (Boost) Efficiency vs Output Current (Boost) 10000 100 90 90 1000 60 100 50 CCM EFFICIENCY 40 PULSE-SKIPPING 10 EFFICIENCY 30 BURST LOSS BURST 20 1 EFFICIENCY CCM LOSS 10 PULSE-SKIPPING LOSS 0.1 0 0.01 1 10 0.0001 0.001 0.
LTC3859 TYPICAL PERFORMANCE CHARACTERISTICS INTVCC and EXTVCC vs Load Current INTVCC Line Regulation 5.5 5.50 EXTVCC Switchover and INTVCC Voltages vs Temperature 6.0 VBIAS = 12V 5.8 EXTVCC AND INTVCC VOLTAGE (V) 5.45 INTVCC VOLTAGE (V) INTVCC VOLTAGE (V) 5.4 5.3 5.2 5.40 EXTVCC = 0V EXTVCC = 8.5V 5.35 5.30 5.25 5.1 5.20 5.0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 5.
LTC3859 TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Current vs Input Voltage Shutdown Current vs Temperature Quiescent Current vs Temperature 25 22 100 18 16 14 12 90 20 QUIESCENT CURRENT (μA) SHUTDOWN CURRENT (μA) SHUTDOWN CURRENT (μA) 20 15 10 5 0 –20 5 30 55 80 TEMPERATURE (°C) 105 130 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 –20 5 30 55 80 TEMPERATURE (°C) 105 130 3859 G30 Undervoltage Lockout Threshold vs Temperature 600 4.4 4.3 FREQ = INTVCC 550 RISING 4.
LTC3859 PIN FUNCTIONS (QFN/TSSOP) FREQ (Pin 1/Pin 5): The Frequency Control Pin for the Internal VCO. Connecting the pin to GND forces the VCO to a fixed low frequency of 350kHz. Connecting the pin to INTVCC forces the VCO to a fixed high frequency of 535kHz. Other frequencies between 50kHz and 900kHz can be programmed using a resistor between FREQ and GND. The resistor and an internal 20μA source current create a voltage used by the internal oscillator to set the frequency.
LTC3859 PIN FUNCTIONS (QFN/TSSOP) TRACK/SS1, TRACK/SS2, SS3 (Pins 34, 16, 3/Pins 38, 20, 7): External Tracking and Soft-Start Input. For the buck channels, the LTC3859 regulates the VFB1,2 voltage to the smaller of 0.8V, or the voltage on the TRACK/SS1,2 pin. For the boost channel, the LTC3859 regulates the VFB3 voltage to the smaller of 1.2V, or the voltage on the SS3 pin. An internal 1μA pull-up current source is connected to this pin.
4.7V EXTVCC VBIAS FREQ + – LDO LDO EN 5.4V SGND SYNC DET CLP VCO 5.4V EN 100k 20μA + – + – CLK1 CLK2 INTVCC PFD 0.72V VFB1 0.88V RUN 11V SHDN RST 2(VFB) 6μA CH1 0.5μA CH2 + – BOT FOLDBACK SLEEP SHDN TOPON + – –+ SLOPE COMP 2.8V 0.65V Q R ICMP Q DROPOUT DET S BUCK CHANNELS 1 AND 2 3mV –+ PGOOD1 OV + – SHDN + – + EA – – IR SWITCHING LOGIC 1μA 0.88V PGND BG SW TG TRACK/SS ITH VFB SENSE– SENSE+ INTVCC 0.
OV3 + – VFB3 1.32V PLLIN/MODE CLK1 RUN3 Q R 11V 0.5μA SHDN + – SNSLO 1μA OV + – 2mV 1.32V + – SS3 ITH3 VFB3 SENSE3+ SENSE3– PGND BG3 SW3 TG3 BOOST3 INTVCC 1.2V SS3 BOT TOP + EA – – 2V IR SWITCHING LOGIC + +– – SLEEP SHDN BOTON SNSLO + – –+ ICMP 0.425V Q S SLOPE COMP 2.8V 0.
LTC3859 OPERATION (Refer to Functional Diagram) Main Control Loop The LTC3859 uses a constant frequency, current mode step-down architecture. The two buck controllers, channels 1 and 2, operate 180 degrees out of phase with each other. The boost controller, channel 3, operates in phase with channel 1.
LTC3859 OPERATION the 0.8V internal reference for the bucks and the 1.2V internal reference for the boost, the LTC3859 regulates the VFB voltage to the TRACK/SS pin voltage instead of the corresponding reference voltage. This allows the TRACK/SS pin to be used to program a soft-start by connecting an external capacitor from the TRACK/SS pin to SGND. An internal 1μA pull-up current charges this capacitor creating a voltage ramp on the TRACK/SS pin. As the TRACK/SS voltage rises linearly from 0V to 0.8V/1.
LTC3859 OPERATION Frequency Selection and Phase-Locked Loop (FREQ and PLLIN/MODE Pins) The selection of switching frequency is a tradeoff between efficiency and component size. Low frequency operation increases efficiency by reducing MOSFET switching losses, but requires larger inductance and/or capacitance to maintain low output ripple voltage. The switching frequency of the LTC3859’s controllers can be selected using the FREQ pin.
LTC3859 OPERATION Buck Controller Output Overvoltage Protection Buck Foldback Current The two buck channels have an overvoltage comparator that guards against transient overshoots as well as other more serious conditions that may overvoltage their outputs. When the VFB1,2 pin rises by more than 10% above its regulation point of 0.800V, the top MOSFET is turned off and the bottom MOSFET is turned on until the overvoltage condition is cleared.
LTC3859 OPERATION 5V SWITCH 20V/DIV 3.3V SWITCH 20V/DIV INPUT CURRENT 5A/DIV INPUT VOLTAGE 500mV/DIV IIN(MEAS) = 2.53ARMS IIN(MEAS) = 1.55ARMS 3859 F01a (a) 3859 F01b (b) Figure 1. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for Dual Switching Regulators Converting 12V to 5V and 3.3V at 3A Each.
LTC3859 APPLICATIONS INFORMATION The Typical Application on the first page is a basic LTC3859 application circuit. LTC3859 can be configured to use either DCR (inductor resistance) sensing or low value resistor sensing. The choice between the two current sensing schemes is largely a design trade-off between cost, power consumption, and accuracy. DCR sensing is becoming popular because it saves expensive current sensing resistors and is more power efficient, especially in high current applications.
LTC3859 APPLICATIONS INFORMATION VIN1,2 (VOUT3) INTVCC BOOST TG LTC3859 RSENSE SW VOUT1,2 (VIN3) BG SENSE1,2+ (SENSE3–) SENSE1, 2– (SENSE3+) CAP PLACED NEAR SENSE PINS SGND 3859 F04a 4a.
LTC3859 APPLICATIONS INFORMATION The maximum power loss in R1 is related to duty cycle. For the buck controllers, the maximum power loss will occur in continuous mode at the maximum input voltage: PLOSS R1= (VIN(MAX) − VOUT ) • VOUT R1 For the boost controller, the maximum power loss in R1 will occur in continuous mode at VIN = 1/2•VOUT : PLOSS R1= (VOUT(MAX) − VIN ) • VIN R1 Ensure that R1 has a power rating higher than this value.
LTC3859 APPLICATIONS INFORMATION The peak-to-peak drive levels are set by the INTVCC voltage. This voltage is typically 5.4V during start-up (see EXTVCC Pin Connection). Consequently, logic-level threshold MOSFETs must be used in most applications. Pay close attention to the BVDSS specification for the MOSFETs as well; many of the logic level MOSFETs are limited to 30V or less.
LTC3859 APPLICATIONS INFORMATION a good compromise for both regions of operation due to the relatively small average current. Larger diodes result in additional transition losses due to their larger junction capacitance. Boost CIN, COUT Selection The input ripple current in a boost converter is relatively low (compared with the output ripple current), because this current is continuous. The boost input capacitor CIN voltage rating should comfortably exceed the maximum input voltage.
LTC3859 APPLICATIONS INFORMATION The total RMS power lost is lower when both controllers are operating due to the reduced overlap of current pulses required through the input capacitor’s ESR. This is why the input capacitor’s requirement calculated above for the worst-case controller is adequate for the dual controller design. Also, the input protection fuse resistance, battery resistance, and PC board trace resistance losses are also reduced due to the reduced peak currents in a 2-phase system.
LTC3859 APPLICATIONS INFORMATION VX(MASTER) VOUT(SLAVE) TIME OUTPUT (VOUT) OUTPUT (VOUT) VX(MASTER) VOUT(SLAVE) TIME 3859 F07a 7a. Coincident Tracking 3859 F07b 7b. Radiometric Tracking Figure 7. Two Different Modes of Output Voltage Tracking VOUT RB LTC3859 VFB1,2 RA VX RTRACKB TRACK/SS1,2 RTRACKA 3859 F08 Figure 8.
LTC3859 APPLICATIONS INFORMATION To prevent the maximum junction temperature from being exceeded, the input supply current must be checked while operating in continuous conduction mode (PLLIN/MODE = INTVCC) at maximum VIN. 2. EXTVCC connected directly to the output voltage of one of the buck regulators. This is the normal connection for a 5V to 14V regulator and provides the highest efficiency. When the voltage applied to EXTVCC rises above 4.7V, the VBIAS LDO is turned off and the EXTVCC LDO is enabled.
LTC3859 APPLICATIONS INFORMATION on, the boost voltage is above the input supply: VBOOST = VIN + VINTVCC (VBOOST = VOUT + VINTVCC for the boost controller). The value of the boost capacitor CB needs to be 100 times that of the total input capacitance of the topside MOSFET(s). The reverse breakdown of the external Schottky diode must be greater than VIN(MAX) for the buck channels and VOUT(MAX) for the boost channel.
LTC3859 APPLICATIONS INFORMATION at a frequency correspond to the frequency set by the FREQ pin. Once prebiased, the PLL only needs to adjust the frequency slightly to achieve phase-lock and synchronization. Although it is not required that the free-running frequency be near external clock frequency, doing so will prevent the operating frequency from passing through a large range of frequencies as the PLL locks.
LTC3859 APPLICATIONS INFORMATION Efficiency Considerations Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3859 circuits: 1) IC VIN current, 2) INTVCC regulator current, 3) I2R losses, 4) Topside MOSFET transition losses. RSENSE, but is “chopped” between the topside MOSFET and the synchronous MOSFET.
LTC3859 APPLICATIONS INFORMATION amount equal to DILOAD(ESR), where ESR is the effective series resistance of COUT. DILOAD also begins to charge or discharge COUT generating the feedback error signal that forces the regulator to adapt to the current change and return VOUT to its steady-state value. During this recovery time VOUT can be monitored for excessive overshoot or ringing, which would indicate a stability problem.
LTC3859 APPLICATIONS INFORMATION The RSENSE resistor value can be calculated by using the minimum value for the maximum current sense threshold (43mV): RSENSE ≤ 43mV = 0.006Ω 6.88A Choosing 1% resistors: RA = 25k and RB = 80.6k yields an output voltage of 3.33V. The power dissipation on the top side MOSFET can be easily estimated. Choosing a Fairchild FDS6982S dual MOSFET results in: RDS(ON) = 0.035Ω/0.022Ω, CMILLER = 215pF. At maximum input voltage with T(estimated) = 50°C: 3.3V PMAIN = (6A)2 {1+ (0.
LTC3859 APPLICATIONS INFORMATION 6. Keep the switching nodes (SW1, SW2, SW3), top gate nodes (TG1, TG2, TG3), and boost nodes (BOOST1, BOOST2, BOOST3) away from sensitive small-signal nodes, especially from the opposites channel’s voltage and current sensing feedback pins. All of these nodes have very large and fast moving signals and therefore should be kept on the output side of the LTC3859 and occupy minimum PC trace area. 7.
LTC3859 APPLICATIONS INFORMATION SW1 L1 D1 RSENSE1 VOUT1 COUT1 RL1 VIN RIN CIN SW2 BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. D2 L2 RSENSE2 VOUT2 COUT2 RL2 3859 F11 Figure 11.
LTC3859 TYPICAL APPLICATIONS VOUT1 RB1 357k OPT RA1 68.1k VFB1 LTC3859 SENSE1– C1 1nF CITH1A 100pF SENSE1+ RITH1 15k CITH1 1500pF 100k ITH1 CSS1 0.1μF MTOP1 TG1 TRACK/SS1 FREQ PLLIN/MODE SW1 RUN1 RB2 649k 10pF RUN3 VFB2 CITH2 2.2nF CBIAS 10μF PGND EXTVCC C2 10μF INTVCC D2 TG2 CSS2 0.1μF TRACK/SS2 MTOP2 CB2 0.1μF BOOST2 L2 6.5μH RSENSE2 8mΩ SW2 VOUT3 RA3 68.1k COUT1 220μF D1 CINT1 4.7μF CITH2A 68pF VOUT1 5V 5A VBIAS RITH2 15k ITH2 RSENSE1 6mΩ MBOT1 BG1 RUN2 RA2 68.
LTC3859 TYPICAL APPLICATIONS VOUT1 RB1 475k 33pF RA1 34k VFB1 LTC3859 SENSE1– C1 1nF CITH1A 100pF SENSE1+ RITH1 10k CITH1 680pF 100k ITH1 CSS1 0.1μF FREQ PLLIN/MODE SW1 RUN1 RB2 215k 15pF RUN3 VFB2 CITH2 820pF COUT1 47μF D1 CBIAS 10μF PGND EXTVCC CINT1 4.7μF CITH2A 150pF VOUT1 12V 3A VBIAS RITH2 15k ITH2 RSENSE1 9mΩ MBOT1 BG1 RUN2 VOUT2 L1 8.8μH CB1 0.1μF BOOST1 SGND C2 10μF INTVCC D2 TG2 CSS2 0.1μF TRACK/SS2 MTOP2 CB2 0.1μF BOOST2 L2 3.
LTC3859 TYPICAL APPLICATIONS VOUT1 RA1 115k RB1 28.7k 56pF VFB1 CITH1A 200pF LTC3859 SENSE1– C1 1nF SENSE1+ RITH1 3.93k CITH1 1000pF 100k ITH1 CSS1 0.01μF FREQ PLLIN/MODE SW1 RUN1 RB2 57.6k 56pF RUN3 VFB2 CITH2 1000pF VBIAS CBIAS 10μF PGND EXTVCC CINT1 4.7μF CITH2A 200pF C2 10μF INTVCC D2 TG2 CSS2 0.01μF TRACK/SS2 MTOP2 CB2 0.1μF BOOST2 L2 0.47μH RSENSE2 3.5mΩ VOUT2 1.2V 8A SW2 VOUT3 RA3 12.1k D1 RITH2 3.
LTC3859 TYPICAL APPLICATIONS VOUT1 RB1 57.6k RA1 115k VFB1 CITH1A 100pF LTC3859 SENSE1– C1 1nF SENSE1+ RITH1 5.6k CITH1 2.2nF 100k ITH1 CSS1 0.1μF C1 10μF PGOOD1 MTOP1 TG1 TRACK/SS1 FREQ PLLIN/MODE SW1 RUN1 RB2 357k RA2 115k RUN3 VFB2 CITH2 3.3nF D1 VBIAS CBIAS 10μF PGND EXTVCC CINT1 4.7μF RITH2 9.1k ITH2 CITH2A 100pF VOUT1 1.2V 3A COUT1 220μF MBOT1 BG1 RUN2 VOUT2 RSENSE1 9mΩ CB1 0.1μF BOOST1 SGND L1 2.2μH C2 10μF INTVCC D2 TG2 CSS2 0.1μF TRACK/SS2 MTOP2 CB2 0.
LTC3859 PACKAGE DESCRIPTION FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev A) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 2.74 REF 4.50 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3.
LTC3859 PACKAGE DESCRIPTION UHF Package 38-Lead Plastic QFN (5mm ¥ 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 p 0.05 5.50 p 0.05 5.15 ± 0.05 4.10 p 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 5.5 REF 6.10 p 0.05 7.50 p 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 p 0.10 0.75 p 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 s 45o CHAMFER 3.00 REF 37 0.00 – 0.05 38 0.40 p0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 7.00 p 0.10 5.
LTC3859 REVISION HISTORY REV DATE DESCRIPTION A 10/10 Updated Note Numbers PAGE NUMBER Updated Notes 2 and 3 text Changed 1.2V to 1.19V in RUN pin text Updated Typical Applications 2, 3, 4, 5 6 11, 15 35, 36, 37, 38, 42 3859fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
LTC3859 TYPICAL APPLICATION High Efficiency Wide Input Range Dual 3.3V/8.5V Converter VOUT1 RA1 68.1k RB1 215k 15pF LTC3859 SENSE1– VFB1 C1 1nF CITH1A 150pF SENSE1+ RITH1 15k CITH1 820pF 100k CSS1 0.1μF ITH1 FREQ PLLIN/MODE SW1 RUN1 RB2 649k CITH2 2.2nF RUN3 COUT1 150μF D1 CBIAS 10μF PGND VFB2 EXTVCC ITH2 INTVCC CINT1 4.7μF C2 10μF D2 TG2 CSS2 0.1μF TRACK/SS2 CB2 0.1μF BOOST2 MTOP2 L2 6.5μH RSENSE2 8mΩ SW2 VOUT3 RA3 68.1k VOUT1 3.