LTC3865/LTC3865-1 Dual, 2-Phase Synchronous DC/DC Controller with Pin Selectable Outputs DESCRIPTION FEATURES n n n n n n n n n n n n Dual, 180° Phased Controllers 2-Pin VID Output Voltage Programming from 0.6V to 5V High Efficiency: Up to 95% RSENSE or DCR Current Sensing Phase-Lockable Fixed Frequency 250kHz to 770kHz Adjustable Current Limit Dual N-Channel MOSFET Synchronous Drive Wide VIN Range: 4.
LTC3865/LTC3865-1 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VIN) ......................... –0.3V to 40V Topside Driver Voltages BOOST1, BOOST2.................................. –0.3V to 46V Switch Voltage (SW1, SW2) ......................... –5V to 40V INTVCC, RUN1, RUN2, PGOOD(s), EXTVCC, (BOOST1-SW1), (BOOST2-SW2) ................. –0.3V to 6V SENSE1+, SENSE2+, SENSE1–, SENSE2– VOSENSE1, VOSENSE2 Voltages .................... –0.3V to 5.
LTC3865/LTC3865-1 PIN CONFIGURATION LTC3865-1 TG1 SW1 MODE/PLLIN VID22 FREQ RUN1 SENSE1+ SENSE1– TOP VIEW 32 31 30 29 28 27 26 25 VOSENSE1 1 24 BOOST1 TK/SS1 2 23 BG1 ITH1 3 22 VIN VID11 4 21 INTVCC 33 SGND VID12 5 20 EXTVCC 19 BG2 ITH2 6 TK/SS2 7 18 PGND VOSENSE2 8 17 BOOST2 TG2 SW2 PGOOD1 PGOOD2 RUN2 VID21 SENSE2+ SENSE2– 9 10 11 12 13 14 15 16 UH PACKAGE 32-LEAD (5mm s 5mm) PLASTIC QFN TJMAX = 125°C, θJA = 34°C/W, θJC = 3°C/W EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERE
LTC3865/LTC3865-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 15V, VRUN1,2 = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loops VIN Input Voltage VOSENSE1,2 Output Voltage Sensing (E-Grade) Output Voltage Sensing (I-Grade) 4.5 (Note 4) ITH1,2 Voltage = 1.
LTC3865/LTC3865-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 15V, VRUN1,2 = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS BG RDOWN BG Driver Pull-Down On-Resistance BG Low MIN TYP 1.
LTC3865/LTC3865-1 TYPICAL PERFORMANCE CHARACTERISTICS 80 80 70 70 EFFICIENCY (%) 90 EFFICIENCY (%) 100 90 BURST DCM 50 CCM 40 30 60 100 5 FIGURE 16 CIRCUIT 90 BURST 50 DCM CCM 40 4 EFFICIENCY 80 70 POWER LOSS (W) 100 60 Efficiency and Power Loss vs Input Voltage Efficiency vs Load Current EFFICIENCY (%) Efficiency vs Load Current 3 60 POWER LOSS 2 50 30 20 10 0 0.01 0.1 1 10 LOAD CURRENT (A) 40 20 VIN = 12V VOUT = 1.5V FIGURE 16 CIRCUIT 10 0 0.
LTC3865/LTC3865-1 TYPICAL PERFORMANCE CHARACTERISTICS Tracking Up and Down with External Ramp (Forced Continuous Mode) Quiescent Current vs Input Voltage without EXTVCC INTVCC Line Regulation 5 5.25 5.00 4 VOUT1 = 1.5V 1Ω LOAD 500mV/DIV VOUT2 = 1.2V 1Ω LOAD 500mV/DIV 3 2 4.50 4.25 4.00 3.75 3.50 1 3865 G07 20ms/DIV 4.75 INTVCC VOLTAGE (V) QUIESCENT CURRENT (mA) TK/SS1 TK/SS2 2V/DIV 3.25 0 5 25 20 15 30 INPUT VOLTAGE (V) 10 3.
LTC3865/LTC3865-1 TYPICAL PERFORMANCE CHARACTERISTICS Shutdown (RUN) Threshold vs Temperature 1.5 1.3 ON 1.2 OFF 1.1 1.0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 1000 900 0.606 OSCILLATOR FREQUENCY (kHz) REGULATED FEEDBACK VOLTAGE (V) 0.608 1.4 RUN PIN VOLTAGE (V) Oscillator Frequency vs Temperature Regulated Feedback Voltage vs Temperature 0.604 0.602 0.600 0.598 700 600 VFREQ = 1.2V 500 400 VFREQ = 0V 300 200 0.
LTC3865/LTC3865-1 PIN FUNCTIONS (QFN/TSSOP) VOSENSE1, VOSENSE2 (Pins 1, 8/Pins 5, 13): When the internal programmable resistive divider is used, these pins must be connected to their corresponding outputs. When an external resistive divider is used, these pins are used for error amplifier feedback inputs. They receive the remotely sensed feedback voltages for each channel directly from the outputs or from the external divider across the outputs.
LTC3865/LTC3865-1 PIN FUNCTIONS (QFN/TSSOP) MODE/PLLIN (Pin 27/Pin 36): Force Continuous Mode, Burst Mode or Pulse-Skip Mode Selection Pin and External Synchronization Input to Phase Detector Pin. Connect this pin to SGND to force both channels in continuous mode of operation. Connect to INTVCC to enable pulse-skip mode of operation. Leaving the pin floating will enable Burst Mode operation.
LTC3865/LTC3865-1 FUNCTIONAL DIAGRAM FREQ/FREQ MODE/PLLIN VID1 VID2 EXTVCC VIN 7.5μA 4.7V INPUT VID LOGIC AND RESISTIVE DIVIDERS MODE/SYNC DETECT F 0.
LTC3865/LTC3865-1 OPERATION Main Control Loop The LTC3865/LTC3865-1 are constant-frequency, current mode step-down controllers with two channels operating 180 degrees out-of-phase. During normal operation, each top MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the main current comparator, ICMP , resets the RS latch.
LTC3865/LTC3865-1 OPERATION pin to a DC voltage below 0.6V (e.g., SGND). To select pulse-skipping mode of operation, tie the MODE/PLLIN pin to INTVCC. To select Burst Mode operation, float the MODE/PLLIN pin. When a controller is enabled for Burst Mode operation, the peak current in the inductor is set to approximately one-third of the maximum sense voltage even though the voltage on the ITH pin indicates a lower value.
LTC3865/LTC3865-1 OPERATION bad mask is 100μs when there are any VID transitions. On the LTC3865-1 (UH32 package) or the LTC3865 (FE38 package), each channel has its own PGOOD pin. Therefore, the PGOOD pins now only respond to their own channels. The PGOOD pins are allowed to be pulled up by external resistors to sources of up to 6V.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION Filter components mutual to the sense lines should be placed close to the LTC3865/LTC3865-1, and the sense lines should run close together to a Kelvin connection underneath the current sense element (shown in Figure 1). Sensing current elsewhere can effectively add parasitic inductance and capacitance to the current sense element, degrading the information at the sense terminals and making the programmed current limit unpredictable.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION the sense traces on the PCB. A typical filter consists of two series 10Ω resistors connected to a parallel 1000pF capacitor, resulting in a time constant of 20ns. This same RC filter, with minor modifications, can be used to extract the resistive component of the current sense signal in the presence of parasitic inductance. For example, Figure 3 illustrates the voltage waveform across a 2mΩ sense resistor with a 2010 footprint for the 1.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION always the same and varies with temperature; consult the manufacturers’ data sheets for detailed information.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION Lower ripple current reduces core losses in the inductor, ESR losses in the output capacitors, and output voltage ripple. Thus, highest efficiency operation is obtained at low frequency with a small ripple current. Achieving this, however, requires a large inductor. A reasonable starting point is to choose a ripple current that is about 40% of IOUT(MAX). Note that the largest ripple current occurs at the highest input voltage.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION which are highest at high input voltages. For VIN < 20V the high current efficiency generally improves with larger MOSFETs, while for VIN > 20V the transition losses rapidly increase to the point that the use of a higher RDS(ON) device with lower CMILLER actually provides higher efficiency.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION VOUT1 OUTPUT VOLTAGE OUTPUT VOLTAGE VOUT1 VOUT2 VOUT2 TIME TIME (5a) Coincident Tracking 3865 F05 (5b) Ratiometric Tracking Figure 5. Two Different Modes of Output Voltage Tracking VOUT1 VOUT1 VOUT2 nR3 R1 TO TK/SS2 PIN R3 R2 R1 TO TK/SS2 PIN TO TO EA1 EA2 nR4 VOUT2 nR1 TO TO EA1 EA2 nR2 R4 R3 R2 R4 38551 F06 (6a) Coincident Tracking Setup (6b) Ratiometric Tracking Setup Figure 6.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION When the master channel’s output experiences dynamic excursion (under load transient, for example), the slave channel output will be affected as well. For better output regulation, use the coincident tracking mode instead of ratiometric. INTVCC Regulators and EXTVCC The LTC3865 features a true PMOS LDO that supplies power to INTVCC from the VIN supply. INTVCC powers the gate drivers and much of the LTC3865/LTC3865-1’s internal circuitry.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION For applications where the main input power is below 5V, tie the VIN and INTVCC pins together and tie the combined pins to the 5V input with a 1Ω or 2.2Ω resistor as shown in Figure 8 to minimize the voltage drop caused by the gate charge current. This will override the INTVCC linear regulator and will prevent INTVCC from dropping too low due to the dropout voltage.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION maximum RMS current of one channel must be used. The maximum RMS capacitor current is given by: CIN Re quired IRMS ≈ 1/ 2 IMAX ⎡⎣( VOUT )( VIN – VOUT ) ⎤⎦ VIN This formula has a maximum 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 manufacturers’ ripple current ratings are often based on only 2000 hours of life.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION Fault Conditions: Current Limit and Current Foldback The LTC3865/LTC3865-1 include current foldback to help limit load current when the output is shorted to ground. If the output falls below 50% of its nominal output level, then the maximum sense voltage is progressively lowered from its maximum programmed value to one-third of the maximum value. Foldback current limiting is disabled during the soft-start or tracking up.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION If the external clock frequency is greater than the internal oscillator’s frequency, fOSC, then current is sourced continuously from the phase detector output, pulling up the filter network. When the external clock frequency is less than fOSC, current is sunk continuously, pulling down the filter network.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION Supplying INTVCC power through EXTVCC from an output-derived source will scale the VIN current required for the driver and control circuits by a factor of (Duty Cycle)/(Efficiency). For example, in a 20V to 5V application, 10mA of INTVCC current results in approximately 2.5mA of VIN current. This reduces the mid-current loss from 10% or more (if the driver was powered directly from VIN) to only a few percent. 3.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION The ITH series RC-CC filter sets the dominant pole-zero loop compensation. The values can be modified slightly (from 0.5 to 2 times their suggested values) to optimize 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 selected because the various types and values determine the loop gain and phase.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION VID11 TK/SS1 RPU2 PGOOD PGOOD VPULL-UP ITH1 LTC3865 VOSENSE1 SENSE1+ SENSE1– VID12 VID21 L1 VID22 VOUT1 TG1 SW1 CB1 BOOST1 FREQ ILIM fIN RSENSE M1 BG1 RIN MODE/PLLIN M2 CERAMIC COUT1 + VIN CVIN RUN1 D1 PGND VIN INTVCC SENSE2+ BG2 VOSENSE2 BOOST2 CINTVCC CERAMIC + SENSE2– CIN M3 GND M4 + SGND EXTVCC + RUN2 COUT2 D2 CB2 SW2 ITH2 TK/SS2 RSENSE TG2 VOUT2 L2 3865 F12 Figure 12.
LTC3865/LTC3865-1 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 3865 F13 Figure 13.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION 6. Keep the switching nodes (SW1, SW2), top gate nodes (TG1, TG2), and boost nodes (BOOST1, BOOST2) away from sensitive small-signal nodes, especially from the opposite 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 LTC3865/LTC3865-1 and occupy minimum PC trace area.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION Design Example As a design example for a 2-channel medium current regulator, assume VIN = 12V (nominal), VIN = 20V (maximum), VOUT1 = 3.3V, VOUT2 = 1.8V, IMAX1,2 = 5A, and f = 500kHz (see Figure 14). The regulated output voltages are set by connecting VID11 and VID22 to INTVCC and floating VID12 and VID21. The frequency is set by biasing the FREQ pin to 1.2V (see Figure 9). The inductance values are based on a 35% maximum ripple current assumption (1.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION With ILIM floating, the equivalent RSENSE resistor value can be calculated by using the minimum value for the maximum current sense threshold (44mV). VSENSE(MIN) RSENSE(EQUIV ) = ΔIL(NOM) ILOAD(MAX ) + 2 44mV = ≅ 7.7mΩ 1.5A 5A + 2 The equivalent RSENSE is the same for Channel 2. The Coiltronics (Cooper) HCP0703-2R2 (20mΩ DCRMAX at 20°C) and HCP0703-3R3 (30mΩ DCRMAX at 20°C) are chosen. At 100°C, the estimated maximum DCR values are 26.4mΩ and 39.6mΩ.
LTC3865/LTC3865-1 APPLICATIONS INFORMATION A short-circuit to ground will result in a folded back current of: ISC = CIN is chosen for an RMS current rating of at least 2A at temperature assuming only channel 1 or 2 is on. COUT is chosen with an 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: (1/ 3) 50mV – 1 ⎛ 90ns(20V) ⎞ = 1.8 A 2 ⎜⎝ 0.008Ω 3.
LTC3865/LTC3865-1 TYPICAL APPLICATIONS 10μF 35V 1μF 2.2Ω + 10μF 35V VIN 7V TO 20V 22μF 50V 4.7μF D3 RJK0305DPB TG1 0.1μF L1 0.47μH TG2 BOOST1 SW1 RJK0330DPB LTC3865 BG1 ILIM 100Ω 100Ω RUN1 1.21k 1% TK/SS1 RJK0330DPB PGND 100Ω 0.1μF RUN2 – 6800pF COUT1 220μF BG2 SENSE2+ SENSE2– SENSE1 VID11 VID12 VOSENSE1 ITH1 + L2 0.47μH FREQ SENSE1+ 0.1μF RJK0305DPB 0.1μF BOOST2 SW2 MODE/PLLIN 2mΩ D4 VIN PGOOD EXTVCC INTVCC 2mΩ 100Ω VID21 VID22 1.
LTC3865/LTC3865-1 PACKAGE DESCRIPTION UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693 Rev D) 0.70 p0.05 5.50 p0.05 4.10 p0.05 3.45 p 0.05 3.50 REF (4 SIDES) 3.45 p 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.75 p 0.05 R = 0.05 TYP 0.00 – 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 s 45o CHAMFER R = 0.115 TYP 31 32 0.40 p 0.
LTC3865/LTC3865-1 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) 0.50 – 0.75 (.020 – .030) 0.09 – 0.20 (.0035 – .0079) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2.
LTC3865/LTC3865-1 REVISION HISTORY REV DATE DESCRIPTION A 04/10 Updated Temperature Range in Order Information Section Updated Electrical Characteristics Table and Note 2 B 08/10 PAGE NUMBER 2 4, 5 Updated Graph G08 7 Added Two Graphs to Typical Application 34 Updated Related Parts 38 Added (Note 9) notation to Absolute Maximum Ratings section 2 Added (Note 8) notation to Electrical Characteristics section 4 Added Condition to IFREQ in Electrical Characteristics section 5 Added Note 9 C
LTC3865/LTC3865-1 TYPICAL APPLICATION 3.3μF 50V 2.2Ω 4.7μF D3 CMDSH-3 HAT2266H 0.004Ω TG1 HAT2266H 1nF COUT1 220μF s2 1800pF 17.8k 1% TK/SS1 100pF 1nF RUN2 – SENSE2– SENSE1 VID11 VID12 VOSENSE1 ITH1 10k 1% 100Ω SENSE2+ RUN1 49.9k 1% + FREQ SENSE1+ 100Ω 0.004Ω PGND ILIM 100Ω L2 1.2μH HAT2266H BG2 MODE/PLLIN HAT2266H 0.1μF BOOST2 SW2 LTC3865 BG1 PLLIN 400kHz VOUT1 3.6V 10A TG2 BOOST1 SW1 VIN 7V TO 36V CIN1 22μF 50V D4 CMDSH-3 VIN PGOOD EXTVCC INTVCC 0.1μF L1 2.
