LTC3609 32V, 6A 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 6A Output Current Wide VIN Range = 4V to 32V (36V Maximum) Internal N-Channel MOSFETs True Current Mode Control Optimized for High Step-Down Ratios tON(MIN) ≤ 100ns Extremely Fast Transient Response Stable with Ceramic COUT ±1% 0.
LTC3609 Absolute Maximum Ratings Pin Configuration (Note 1) 41 SW 42 SW 43 SW 44 SW 45 SW 46 SW 47 SW 48 PVIN 49 PVIN 50 PVIN 51 PVIN TOP VIEW 52 PVIN Input Supply Voltage (SVIN, PVIN, ION)........ 36V to –0.3V Boosted Topside Driver Supply Voltage (BOOST)................................................. 42V to –0.3V SW Voltage............................................. 36V to –0.3V INTVCC, EXTVCC, (BOOST – SW), RUN/SS, PGOOD Voltages....................................... 7V to –0.
LTC3609 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 15V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop SVIN Operating Input Voltage Range IQ Input DC Supply Current Normal Shutdown Supply Current VFB Feedback Reference Voltage 4 ITH = 1.2V (Note 3) –40°C to 85°C –40°C to 125°C l 0.594 0.
LTC3609 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 15V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 4.7 5 5.5 V –0.
LTC3609 Typical Performance Characteristics Efficiency vs Load Current Efficiency vs Input Voltage 100 100 FCB = 5V FIGURE 6 CIRCUIT 90 80 40 30 ILOAD = 6A 90 ILOAD = 1A 85 20 10 VIN = 12V FREQUENCY = 550kHz 0 0.01 0.1 1 LOAD CURRENT (A) 80 10 FREQUENCY (kHz) 50 EFFICIENCY (%) EFFICIENCY (%) 60 600 95 VOUT = 5V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V VOUT = 1.5V VOUT = 1.
LTC3609 Typical Performance Characteristics Maximum Valley Current Limit vs VRNG Voltage On-Time vs Temperature MAXIMUM VALLEY CURRENT LIMIT (A) 250 ON-TIME (ns) 15 IION = 30µA VVON = 0V 200 150 100 50 0 –50 –25 25 75 0 50 TEMPERATURE (°C) 100 15 FIGURE 6 CIRCUIT MAXIMUM VALLEY CURRENT LIMIT (A) 300 Maximum Valley Current Limit vs RUN/SS Voltage 12 9 6 3 0 125 0.5 0.6 0.7 0.8 0.9 1.0 VRNG VOLTAGE (V) 1.1 FIGURE 6 CIRCUIT 12 9 6 3 0 1.65 1.90 2.15 2.40 2.65 2.90 3.15 3.
LTC3609 Typical Performance Characteristics EXTVCC Switch Resistance vs Temperature INTVCC Load Regulation EXTVCC SWITCH RESISTANCE (Ω) 0.20 ∆INTVCC (%) 0.10 0 –0.10 –0.20 –0.30 –0.40 0 40 10 20 30 INTVCC LOAD CURRENT (mA) 10 25 8 20 IEXTVCC (mA) 0.
LTC3609 Pin Functions PVIN (Pins 1, 2, 3, 4, 5, 6, 7, 48, 49, 50, 51, 52, 53): Main Input Supply. Decouple this pin to power PGND with the input capacitance, CIN. SW (Pins 8, 33, 41, 42, 43, 44, 45, 46, 47, 55): 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. NC (Pins 9, 21, 24, 25, 28): No Connection. SGND (Pins 10, 14, 15, 20, 26, 27, 54): Signal Ground.
LTC3609 Functional Diagram RON VON ION 13 22 FCB EXTVCC 19 29 SVIN 30 4.7V 0.7V 2.4V + 1µA PVIN – 1, 2, 3, 4, 5, 6, 7, 48, 49, 50, 51, 52, 53 0.6V REF 0.6V CIN 5V REG INTVCC + – 31, 32 F 11 VVON tON = (10pF) IION R S Q FCNT SW + ICMP – L1 DB VOUT 8, 33, 41, 42, 43, 44, 45, 46, 47, 55 SWITCH LOGIC IREV – SHDN 1.4V COUT OV M2 + CVCC 17 PGND s 34, 35, 36, 37, 38, 39, 40 (0.5 TO 2) 0.7V 16 PGOOD 1 240k + 1V Q2 Q4 – Q6 ITHB R2 0.
LTC3609 Operation Main Control Loop The LTC3609 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 4V to 32V/36V maximum and provides a regulated output voltage at up to 6A of output current. The internal synchronous power switch increases efficiency and eliminates the need for an external Schottky diode.
LTC3609 Applications Information The basic LTC3609 application circuit is shown on the front page of this data sheet. External component selection is primarily determined by the maximum load current. The LTC3609 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.
LTC3609 Applications Information 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 RON 0.7 V Changes in the load current magnitude will also cause frequency shift.
LTC3609 Applications Information 2.0 CVON 0.01µF RVON2 100k RC VON LTC3609 ITH CC (2a) VOUT INTVCC RVON1 3k 10k CVON 0.01µF RVON2 10k RC Q1 2N5087 CC VON LTC3609 ITH DROPOUT REGION 1.0 0.5 0 0.25 0.50 0.75 DUTY CYCLE (VOUT/VIN) 1.0 3609 F03 Figure 3. Maximum Switching Frequency vs Duty Cycle 3609 F02 Figure 2.
LTC3609 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.
LTC3609 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 LTC3609 has a current mode controller which inherently limits the cycle-by-cycle inductor current not only in steady-state operation but also in transient.
LTC3609 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.
LTC3609 Applications Information INTVCC RSS* VIN 3.3V OR 5V D1 RUN/SS RSS* CSS D2* RUN/SS 2N7002 CSS 3609 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%.
LTC3609 Applications Information Design Example Next, set up VRNG voltage and check the ILIMIT. Tying VRNG to GND will set the typical current limit to 9A, and tying VRNG to 1.2V will result in a typical current around 14A. CIN is chosen for an RMS current rating of about 5A at 85°C. The ceramic output capacitors are chosen for an ESR of 0.002Ω to minimize output voltage changes due to inductor ripple current and load steps.
LTC3609 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.
LTC3609 Applications Information CVCC SW NC SGND SVIN EXTVCC INTVCC SW PGND PGND PGND PGND INTVCC NC LTC3609 SW SGND FCB PVIN ITH PVIN VRNG PVIN PGOOD PVIN SGND 2 3 4 5 6 7 8 9 10 11 12 13 14 VON 1 DB CB 26 25 R1 R2 24 23 RON 22 21 20 19 RC 18 CC1 17 16 15 CC2 SGND PVIN RUN/SS 52 SW BOOST 51 ION SGND 50 SW NC 49 VFB SW CIN SW PVIN 48 NC PVIN 47 SW PVIN 46 NC PVIN 45 SW PVIN 44 PGND PGND 43 SGND PVIN 42 SW PVIN 41 VOUT PGND 4
LTC3609 Typical Applications 3.6V Input to 1.5V/6A at 750kHz INTVCC VBIAS 5V CF 0.1µF 50V CVCC 4.7µF 6.3V EXTVCC C4 0.01µF SW GND R2 60.4k 1% 52 NC SGND SVIN EXTVCC INTVCC SW INTVCC PGND PGND PGND PGND PGND PGND SW SGND PVIN FCB PVIN ITH PVIN VRNG PVIN PGOOD PVIN SGND 1 2 3 4 5 6 7 8 9 10 11 KEEP POWER GROUND AND SIGNAL GROUND SEPARATE. CONNECT AT ONE POINT. INTVCC DB CMDSH-3 24 RON 113k 1% 23 22 INTVCC VIN 21 JP1 20 19 CC1 1500pF R5 8.
LTC3609 Typical Applications 5V to 32V Input to 1.2V/6A at 550kHz INTVCC CF 0.1µF 25V CVCC 4.7µF 6.3V VIN RF1 1Ω EXTVCC C4 0.01µF SW GND 50 51 52 NC SGND SVIN EXTVCC INTVCC SW INTVCC PGND PGND PGND PGND PGND PGND SW SGND PVIN FCB PVIN ITH PVIN VRNG PVIN PGOOD PVIN SGND 1 2 3 4 5 6 7 8 9 10 11 C5: TAIYO YUDEN JMK316BJ226ML-T CIN: MURATA GRM32ER71H475K COUT: MURATA GRM435R60J167M LI: CDEP850R8MC-88 INTVCC DB CMDSH-3 KEEP POWER GROUND AND SIGNAL GROUND SEPARATE.
LTC3609 Typical Applications 5V to 32V Input to 1.8V/6A All Ceramic 1MHz INTVCC CF 0.1µF 50V CVCC 4.7µF 6.3V VIN RF1 1Ω EXTVCC C4 0.01µF SW GND 51 52 NC SGND SVIN EXTVCC INTVCC SW PGND PGND PGND PGND PGND PGND INTVCC NC LTC3609 SW SGND PVIN FCB PVIN ITH PVIN VRNG PVIN PGOOD PVIN SGND 1 2 3 4 5 6 7 8 9 10 11 INTVCC DB CMDSH-3 KEEP POWER GROUND AND SIGNAL GROUND SEPARATE. CONNECT AT ONE POINT. R1 10k 1% 24 23 22 CVON 0.
LTC3609 Package Description WKG Package 52-Lead QFN Multipad (7mm × 8mm) (Reference LTC DWG # 05-08-1768 Rev Ø) SEATING PLANE A 7.00 BSC 0.00 – 0.05 2.625 REF 41 B PAD 1 CORNER 4 2.90 REF 0.50 BSC 1 40 bbb M C A B 7 8.00 BSC PIN 1 ID 52 3.40 REF 3.90 ± 0.10 3.20 ± 0.10 2.025 ± 0.10 2.925 ± 0.10 3.40 REF 33 8 32 9 1.00 REF 10 aaa C 2x NX b TOP VIEW 0.90 ± 0.10 NX 0.08 C // ccc C 8 7.50 ± 0.05 2.90 REF 0.50 BSC 1.35 ± 0.10 1.775 REF 15 0.25 ± 0.
LTC3609 Revision History REV DATE B 06 /10 (Revision history begins at Rev B) DESCRIPTION PAGE NUMBER Updated SW voltage range in Absolute Maximum Ratings. 2 Note 4 updated. 4 3609fb 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.
LTC3609 Typical Application INTVCC CF 0.1µF 50V CVCC 4.7µF 6.3V VIN RF1 1Ω EXTVCC C4 0.01µF SW GND 50 51 52 NC SGND SVIN EXTVCC INTVCC SW PGND PGND PGND PGND PGND PGND INTVCC NC LTC3609 SW SGND PVIN FCB PVIN ITH PVIN VRNG PVIN PGOOD PVIN SGND 1 2 3 4 5 6 7 8 9 10 11 CIN: MURATA GRM31CR71H475K COUT: SANYO 16SVP180MX LI: CDEP4R3MC-88 INTVCC DB CMDSH-3 KEEP POWER GROUND AND SIGNAL GROUND SEPARATE. CONNECT AT ONE POINT. R1 3.
