LTC3611 10A, 32V Monolithic Synchronous Step-Down DC/DC Converter Description Features n n n n n n n n n n n n n n n n n 10A Output Current Wide VIN Range = 4.5V to 32V (36V Maximum) Internal N-Channel MOSFETs True Current Mode Control Optimized for High Step-Down Ratios t0N(MIN) ≤ 100ns Extremely Fast Transient Response Stable with Ceramic COUT ±1% 0.
LTC3611 Absolute Maximum Ratings Pin Configuration (Note 1) PGND 1 49 SGND 50 SGND 51 SVIN 52 SVIN 53 INTVCC 54 INTVCC 55 SW 56 PGND 57 PGND 58 PGND 59 PGND 60 PGND 61 PGND 62 PGND 63 PGND TOP VIEW 64 PGND Input Supply Voltage (VIN, ION)................... 36V to –0.3V Boosted Topside Driver Supply Voltage (BOOST)................................................. 42V to –0.3V SW Voltage............................................. 36V to –0.
LTC3611 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop VIN Operating Input Voltage Range IQ Input DC Supply Current Normal Shutdown Supply Current VFB Feedback Reference Voltage 4.5 ITH = 1.2V (Note 3) –40°C to 85°C –40°C to 125°C l 0.594 0.590 32 V 900 15 2000 30 µA µA 0.600 0.
LTC3611 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS l 4.7 5 5.6 V –0.1 ±2 % l 4.
LTC3611 Typical Performance Characteristics Efficiency vs Load Current Efficiency vs Input Voltage 100 FCB = 5V FIGURE 6 CIRCUIT DISCONTINUOUS EFFICIENCY (%) 95 80 CONTINUOUS 70 VIN = 12V VOUT = 2.5V EXTVCC = 5V FIGURE 6 CIRCUIT 60 50 0.01 0.1 1 LOAD CURRENT (A) 90 ILOAD = 10A ILOAD = 1A 80 10 5 10 20 25 15 INPUT VOLTAGE (V) 440 30 400 35 FCB = 0V FIGURE 6 CIRCUIT 5 10 15 20 25 INPUT VOLTAGE (V) 30 35 3611 G06 2.5 FIGURE 6 CIRCUIT ITH Voltage vs Load Current FIGURE 6 CIRCUIT 0.
LTC3611 Typical Performance Characteristics ON-TIME (ns) 250 20 IION = 30µA VVON = 0V MAXIMUM VALLEY CURRENT LIMIT (A) 300 200 150 100 50 0 –50 –25 25 75 0 50 TEMPERATURE (°C) 100 Maximum Valley Current Limit vs VRNG Voltage 18 15 10 5 0.5 125 0.6 0.8 0.7 VRNG VOLTAGE (V) 0.9 100 16 14 12 10 8 6 4 125 8 4 12 16 20 24 28 INPUT VOLTAGE (V) 1.9 2.15 2.4 2.65 2.9 3.15 3.4 RUN/SS VOLTAGE (V) 32 36 VRNG = 1V 15 10 5 0 0 0.1 0.2 0.3 0.4 VFB (V) 2.0 0.62 0.5 0.
LTC3611 Typical Performance Characteristics Input and Shutdown Currents vs Input Voltage 1000 25 800 20 SHUTDOWN 600 15 400 10 EXTVCC = 5V 200 0 5 10 20 15 INPUT VOLTAGE (V) 30 25 30 0.20 25 0.10 ∆INTVCC (%) 30 SHUTDOWN CURRENT (µA) INPUT CURRENT (µA) 35 IEXTVCC vs Frequency 0.30 IEXTVCC (mA) EXTVCC OPEN 1200 0 INTVCC Load Regulation 40 1400 0 –0.10 –0.20 5 –0.30 0 –0.40 VIN = 24V VOUT = 2.
LTC3611 Pin Functions PGND (Pins 1, 2, 3, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65): Power Ground. Connect this pin closely to the (–) terminal of CVCC and the (–) terminal of CIN. SW (Pins 4, 5, 6, 7, 8, 9, 10, 11, 26, 55, 66): Switch Node Connection to the Inductor. The (–) terminal of the bootstrap capacitor, CB, also connects here. This pin swings from a diode voltage drop below ground up to VIN. PVIN (Pins 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 67): Main Input Supply.
LTC3611 FUNCTIONAL Diagram RON VON ION 35 41 FCB EXTVCC 39 44 SVIN 51, 52 4.7V 0.7V 2.4V + 1µA PVIN – 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 67 0.6V REF 0.6V 5V REG INTVCC + – 53, 54 F 29 VVON tON = (10pF) IION S Q FCNT CB M1 ON SW + ICMP – L1 DB VOUT 4, 5, 6, 7, 8, 9, 10, 11, 26, 55, 66 SWITCH LOGIC IREV – SHDN 1.4V COUT OV M2 + CVCC 37 PGND × (0.5 TO 2) 1, 2, 3, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 0.
LTC3611 Operation Main Control Loop The LTC3611 is a high efficiency monolithic synchronous, step-down DC/DC converter utilizing a constant on-time, current mode architecture. It operates from an input voltage range of 4.5V to 32V and provides a regulated output voltage at up to 10A of output current. The internal synchronous power switch increases efficiency and eliminates the need for an external Schottky diode.
LTC3611 Applications Information The basic LTC3611 application circuit is shown on the front page of this data sheet. External component selection is primarily determined by the maximum load current. The LTC3611 uses the on-resistance of the synchronous power MOSFET for determining the inductor current. The desired amount of ripple current and operating frequency also determines the inductor value.
LTC3611 Applications Information RON. Figures 1a and 1b show how RON relates to switching frequency for several common output voltages. Because the voltage at the ION pin is about 0.7V, the current into this pin is not exactly inversely proportional to VIN, especially in applications with lower input voltages. To correct for this error, an additional resistor, RON2, connected from the ION pin to the 5V INTVCC supply will further stabilize the frequency. RON2 = 5V R 0.
LTC3611 Applications Information 2.0 CVON 0.01µF RVON2 100k RC VON LTC3611 ITH CC (2a) VOUT INTVCC RVON1 3k 10k CVON 0.01µF RVON2 10k RC Q1 2N5087 CC VON SWITCHING FREQUENCY (MHz) VOUT RVON1 30k 1.5 1.0 0.5 0 LTC3611 ITH DROPOUT REGION 0 0.25 0.50 0.75 DUTY CYCLE (VOUT/VIN) 1.0 3611 F03 Figure 3. Maximum Switching Frequency vs Duty Cycle 3611 F02 (2b) Figure 2.
LTC3611 Applications Information Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores. A variety of inductors designed for high current, low voltage applications are available from manufacturers such as Sumida, Panasonic, Coiltronics, Coilcraft and Toko. CIN and COUT Selection The input capacitance, CIN, is required to filter the square wave current at the drain of the top MOSFET.
LTC3611 Applications Information Fault Conditions: Current Limit and Foldback with changes in VIN. Tying the FCB pin below the 0.6V threshold forces continuous synchronous operation, allowing current to reverse at light loads and maintaining high frequency operation. The LTC3611 has a current mode controller which inherently limits the cycle-by-cycle inductor current not only in steady state operation but also in transient.
LTC3611 Applications Information The EXTVCC pin can be used to provide MOSFET gate drive and control power from the output or another external source during normal operation. Whenever the EXTVCC pin is above 4.7V the internal 5V regulator is shut off and an internal 50mA P-channel switch connects the EXTVCC pin to INTVCC. INTVCC power is supplied from EXTVCC until this pin drops below 4.5V. Do not apply more than 7V to the EXTVCC pin and ensure that EXTVCC ≤ VIN.
LTC3611 Applications Information INTVCC RSS* VIN 3.3V OR 5V D1 RUN/SS RSS* CSS D2* RUN/SS 2N7002 CSS 3611 F05 *OPTIONAL TO OVERRIDE OVERCURRENT LATCHOFF (5a) (5b) Figure 5. RUN/SS Pin Interfacing with Latchoff Defeated Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%.
LTC3611 Applications Information Design Example Next, set up VRNG voltage and check the ILIMIT. Tying VRNG to 1V will set the typical current limit to 15A, and tying VRNG to GND will result in a typical current around 10A. CIN is chosen for an RMS current rating of about 5A at 85°C. The output capacitors are chosen for a low ESR of 0.013Ω to minimize output voltage changes due to inductor ripple current and load steps.
LTC3611 Applications Information How to Reduce SW Ringing As with any switching regulator, there will be voltage ringing on the SW node, especially for high input voltages. The ringing amplitude and duration is dependent on the switching speed (gate drive), layout (parasitic inductance) and MOSFET output capacitance. This ringing contributes to the overall EMI, noise and high frequency ripple. One way to reduce ringing is to optimize layout. A good layout minimizes parasitic inductance.
LTC3611 Applications Information CVCC SW SGND SVIN SGND SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND SW SGND SW FCB SW ITH PVIN VRNG PVIN PGOOD PVIN VON PVIN SGND PVIN PVIN 16 SW 48 47 46 45 R1 44 R2 43 42 41 RON 40 39 RC 38 CC1 37 36 35 34 CC2 33 SGND 15 ION LTC3611 SGND CIN 14 SW RUN/SS 13 SGND BOOST 12 SW SGND 11 VFB NC 9 10 EXTVCC SW SW VOUT SW PVIN 8 SGND PVIN 7 SW PVIN 6 SGND PVIN COUT 5 SGND PGND PVIN 4
LTC3611 TYPICAL ApplicationS 3.3V Input to 1.5V/10A at 750kHz INTVCC CVCC 4.7µF 6.3V PGND CF 0.1µF 50V SW SGND C6 100µF 50V + (OPTIONAL) 12 13 14 15 16 SGND SVIN SGND SVIN INTVCC SW INTVCC PGND PGND PGND PGND PGND PGND PGND PGND SW FCB SW ITH PVIN VRNG PVIN PGOOD PVIN VON PVIN SGND PVIN PVIN CIN 4.7µF 50V ×2 GND SGND 48 VIN2 = 5V C4 0.01µF 47 46 R1 20.43k 1% 45 44 43 C1 (OPTIONAL) R2 30.1k 1% RON 113k 1% 42 41 40 CON 0.
LTC3611 TYPICAL ApplicationS 5V to 24V Input to 1.2V/10A at 550kHz INTVCC CVCC 4.7µF 6.3V PGND VIN CF 0.1µF 50V SW SGND C6 100µF 50V + (OPTIONAL) 12 13 14 15 16 SGND SVIN SGND SVIN INTVCC SW INTVCC PGND PGND PGND PGND PGND PGND PGND PGND SW FCB SW ITH PVIN VRNG PVIN PGOOD PVIN VON PVIN SGND PVIN PVIN CIN 4.7µF 50V ×2 GND SGND 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 CB1 0.
LTC3611 TYPICAL ApplicationS 5V to 28V Input to 1.8V/10A All Ceramic 1MHz INTVCC CVCC 4.7µF 6.3V PGND VIN CF 0.1µF 50V SW SGND CIN 4.7µF 50V ×2 VIN 12 13 14 15 16 SGND SVIN SGND SVIN INTVCC SW PGND PGND PGND PGND PGND PGND PGND PGND INTVCC SGND SW FCB SW ITH PVIN VRNG PVIN PGOOD PVIN VON PVIN SGND PVIN PVIN VIN 5V TO 28V ION LTC3611 SW 48 EXTVCC C4 0.01µF 47 46 R1 10k 1% 45 44 43 R2 20k 1% C1 47pF (OPTIONAL) C2 VOUT RON 102k 1% 42 41 40 CON 0.
LTC3611 Package Description WP Package 64-Lead QFN Multipad (9mm × 9mm) (Reference LTC DWG # 05-08-1812 Rev A) SEATING PLANE A 9.00 BSC 1.39 0.00 – 0.05 1.19 0.20 REF 49 50 51 52 53 54 3.30 0.50 64 0.30 – 0.50 B 1.92 2.01 PAD 1 CORNER 48 0.53 (2x) 1.17 3.06 3.50 0.87 1 0.30 (2x) 2.98 0.95 bbb M C A B 5 9.00 BSC 1.30 4.10 3.99 2.04 33 16 17 32 aaa C 2x TOP VIEW 0.90 ± 0.10 NX 0.08 C // ccc C 6 3.30 0.50 1.81 3.30 NX b aaa C 2x 3.60 4.53 0.20 – 0.30 1.
LTC3611 Revision History (Revision history begins at Rev D) REV DATE DESCRIPTION D 06/10 Updated SW voltage range in Absolute Maximum Ratings. PAGE NUMBER 2 Note 4 updated. 4 3611fd 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3611 Typical Application 14V to 32V Input to 12V/5A at 500kHz CVCC 4.7µF 6.3V INTVCC SW PGND VIN CF 0.1µF 50V SGND VIN VIN 14V TO 32V C6 100µF 50V + (OPTIONAL) 12 13 14 15 16 SGND SVIN SGND SVIN INTVCC SW INTVCC PGND PGND PGND PGND PGND PGND PGND PGND LTC3611 SW SGND SW FCB SW ITH PVIN VRNG PVIN PGOOD PVIN VON PVIN SGND PVIN PVIN CIN 4.7µF 50V ×2 GND ION 48 47 46 EXTVCC C4 0.01µF R1 1.58k 1% 45 44 43 C1 (OPTIONAL) R2 30.
