LTC3375 8-Channel Programmable, Parallelable 1A Buck DC/DCs Features n n n n n n n n n n Description 8-Channel Independent Step-Down DC/DCs Master-Slave Configurable for Up to 4A Per Output Channel with a Single Inductor Independent VIN Supply for Each DC/DC (2.25V to 5.5V) All DC/DCs Have 0.
LTC3375 Table of Contents Features...................................................... 1 Applications................................................. 1 Typical Application ......................................... 1 Description.................................................. 1 Absolute Maximum Ratings............................... 3 Order Information........................................... 3 Pin Configuration........................................... 3 Electrical Characteristics...................
LTC3375 (Note 1) TOP VIEW FB1 1 VIN1 2 SW1 3 SW2 4 VIN2 5 FB2 6 FB3 7 VIN3 8 SW3 9 SW4 10 VIN4 11 FB4 12 36 FB8 35 VIN8 34 SW8 33 SW7 32 VIN7 31 FB7 30 FB6 29 VIN6 28 SW6 27 SW5 26 VIN5 25 FB5 GND 49 EN4 13 EN3 14 IRQ 15 RST 16 CT 17 SYNC 18 RT 19 ON 20 PB 21 KILL 22 EN6 23 EN5 24 VIN1-8, FB1-8, EN1-8, VCC, VSHNT, FBVCC, CT, ON, KILL, IRQ, RST, PB, WDI, WDO, SYNC, RT, SDA, SCL...................................................... –0.3V to 6V TEMP....................–0.3V to Lesser of (VCC + 0.
LTC3375 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified.
LTC3375 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified. SYMBOL PARAMETER CONDITIONS VPGOOD(FALL) Falling PGOOD Threshold Voltage Full-Scale (1, 1, 1, 1) Reference Voltage VPGOOD(HYS) PGOOD Hysteresis MIN TYP MAX UNITS 92.
LTC3375 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified.
LTC3375 Typical Performance Characteristics Buck VIN Undervoltage Threshold vs Temperature 2.30 2.65 2.25 2.60 VCC RISING 2.55 2.50 VCC FALLING 2.45 2.40 60 ALL REGULATORS 55 IN SHUTDOWN 50 2.20 VIN RISING 2.15 2.10 VIN FALLING 2.05 2.00 2.35 0 0 VCC = 3.3V 50 240 VCC = 3.3V 200 VCC = 2.7V 160 2.05 2.00 1.95 0 –50 –25 0 1.80 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) Oscillator Frequency vs RT Oscillator Frequency vs VCC 4.0 2.15 2.15 3.5 2.10 2.10 3.0 2.05 2.05 1.
LTC3375 Typical Performance Characteristics VTEMP vs Temperature 1400 900 ALL REGULATORS DISABLED VCC = 3.3V 1200 850 415 600 400 ACTUAL VTEMP 200 750 EN RISING 700 650 EN FALLING 600 550 500 0 0 20 40 60 80 100 120 TEMPERATURE (°C) 400 –50 –25 140 0 VIN = 2.25V VIN = 3.3V 450 1.86 VIN = 5.5V 400 350 VIN = 2.25V 300 250 1.78 1.76 100 0 VIN = 3.3V 2.5 RDS(ON) (mΩ) IFWD (A) 2.2 2.
LTC3375 Typical Performance Characteristics 3.32 3.30 3.28 3.26 3.24 3.22 3.20 –50 –25 90 6.16 80 6.14 70 6.12 6.10 6.08 20 6.02 10 1A Buck Efficiency vs ILOAD 60 50 VIN = 2.7V VIN = 3.3V VIN = 5.5V VIN = 2.7V VIN = 3.3V VIN = 5.5V FORCED CONTINUOUS MODE 40 30 20 10 1 VOUT = 2.5V fOSC = 2MHz L = 2.2µH 60 50 20 10 0 1 10 100 LOAD CURRENT(mA) VOUT = 1.8V fOSC = 2MHz L = 2.
LTC3375 Typical Performance Characteristics 100 90 90 60 50 VIN = 2.7V VIN = 3.3V VIN = 5.5V VIN = 2.7V VIN = 3.3V VIN = 5.5V FORCED CONTINUOUS MODE 40 30 20 10 0 EFFICIENCY (%) 1 1000 10 100 LOAD CURRENT(mA) VOUT = 2.5V 3375 G28 fOSC = 2MHz L = 2.2µH 70 50 40 80 IL = 500mA 70 IL = 20mA 60 50 40 30 30 20 V OUT = 1.8V 10 IL = 100mA L = 3.3µH 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 FREQUENCY (MHz) 20 1A Buck Efficiency vs ILOAD (Across Operating Frequency) VOUT = 1.8V 10 VIN = 3.3V L = 3.
LTC3375 Typical Performance Characteristics 1A Buck Regulator, Transient Response (Forced Continuous Mode) 1A Buck Regulator, Transient Response (Burst Mode) VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED INDUCTOR CURRENT 200mA/DIV INDUCTOR CURRENT 200mA/DIV 0mA 0mA 3375 G37 50µs/DIV LOAD STEP = 100mA TO 700mA VIN = 3.3V, VOUT = 1.8V 50µs/DIV LOAD STEP = 100mA TO 700mA VIN = 3.3V, VOUT = 1.
LTC3375 Pin Functions FB1 (Pin 1): Buck Regulator 1 Feedback Pin. Receives feedback by a resistor divider connected across the output. VIN1 (Pin 2): Buck Regulator 1 Input Supply. Bypass to GND with a 10µF or larger ceramic capacitor. SW1 (Pin 3): Buck Regulator 1 Switch Node. External inductor connects to this pin. SW2 (Pin 4): Buck Regulator 2 Switch Node. External inductor connects to this pin. VIN2 (Pin 5): Buck Regulator 2 Input Supply. Bypass to GND with a 10µF or larger ceramic capacitor.
LTC3375 Pin Functions ON (Pin 20): Open-Drain Output. When the PB pin is pressed and released, the signal is debounced and the ON signal is held HIGH for a minimum time period that is scaled by the CT capacitor. ON is forced low if: a) KILL is not driven high (by µP) within 10 seconds of the initial valid PB power turn-on event, b) KILL is driven low during normal operation, c) PB is pressed and held low for 10 seconds during normal operation, d) a RESET_ALL I2C command is written.
LTC3375 Pin Functions WDO (Pin 39): Watchdog Timer Output. Open-drain output. WDO is pulled low for 200ms during a watchdog timer failure. WDI (Pin 40): Watchdog Timer Input. The WDI pin must be toggled either low to high or high to low every 1.5 seconds. Failure to toggle WDI results in the WDO pin being pulled low for 200ms. VCC (Pin 41): Always-On LDO Output Voltage/Internal Bias Supply. When used as a regulator, VCC should be connected to the emitter/source of the external LDO NPN/ NFET transistor.
LTC3375 Block Diagram 41 VCC LDO 43 42 18 19 44 2 3 1 48 VSHNT FBVCC + – TOP LOGIC, CT OSCILLATOR TIMING 1.
LTC3375 Operation Buck Switching Regulators The LTC3375 contains eight monolithic 1A synchronous buck switching regulators. All of the switching regulators are internally compensated and need only external feedback resistors to set the output voltage. The switching regulators offer two operating modes: Burst Mode operation (power-up default mode) for higher efficiency at light loads and forced continuous PWM mode for lower noise at light loads.
LTC3375 Operation feedback network connected to the FB1 pin programs the output voltage to 1.2V. The FB2 pin is tied to VIN1/2, which configures buck regulator 2 as the slave. The SW1 and SW2 pins must be tied together, as must the VIN1 and VIN2 pins. The register contents of the master program, the combined buck regulator’s behavior, and the register contents of the slave are ignored. The slave buck control circuitry draws no current.
LTC3375 Operation t PB_ON PB ON (TIED TO EN1) tKILLH KILL = 0 SEQUENCE UP SEQUENCE DOWN BUCK1-BUCK8 3375 F02a HARD RESET t 1 t2 t3 KILL NOT ASSERTED BEFORE t3 Figure 2a. Power-Up Using PB (Sequenced Power-Up, Figure 8) t PB_ON t PB_OFF PB ON (TIED TO EN1) t KILLH KILL DON’T CARE BUCK1-BUCK8 SEQUENCE DOWN SEQUENCE UP IRQ HARD RESET 3375 F02b t1 t2 t3 t4 t5 Figure 2b.
LTC3375 Operation t PB_ON <10 SEC PB ON (TIED TO EN1) t HR KILL BUCK1-BUCK8 SEQUENCE DOWN SEQUENCE UP t PB_LO IRQ t KILLLO HARD RESET t 1 t2 t3 t4 t5 t6 t7 t8 t9 3375 F02d Figure 2d. Power-Up Using PB and Power-Down Using a “Soft” Reset of either an upstream high voltage buck regulator, or any EN pin causing its associated buck switching regulator to power-up, which can sequentially power-up the other buck regulators.
LTC3375 Operation ADDRESS DATA BYTE A WR A7 0 1 1 0 1 0 0 0 SDA 0 1 1 0 1 0 0 0 ACK SCL 1 2 3 4 5 6 7 8 9 A6 A5 A4 A3 DATA BYTE B A2 A1 A0 B7 B6 B5 B4 B3 B2 B1 B0 START STOP ACK 1 2 3 4 5 6 7 8 9 ACK 1 2 3 4 5 6 7 8 9 SDA tSU, DAT tLOW tSU, STA tHD, DAT tHD, STA tBUF tSU, STO 3375 F03 SCL tHIGH tHD, STA START CONDITION tr tSP tf REPEATED START CONDITION STOP CONDITION START CONDITION Figure 3.
LTC3375 Operation Table 1. Summary of I2C Sub-Addresses and Byte Formats. Bits A7, A6, A5, A4 of Sub-Address Need to be 0 to Access Registers SUB-ADDRESS A7A6A5A4A3A2A1A0 OPERATION ACTION Global Logic BYTE FORMAT D7D6D5D4D3D2D1D0 DEFAULT D7D6D5D4D3D2D1D0 COMMENTS 0000 0000 (00h) Read/Write RESET_ALL, DT[1], DT[0], IGNORE_EN, 0000 0000 1KPD, SLOW, RD_TEMP, Unused 0000 0001 (01h) Read/Write Buck1 Register ENABLE, MODE, PHASE[1], PHASE[0], DAC[3], DAC[2].
LTC3375 Operation the write address is 68h and the read address is 69h. The LTC3375 will acknowledge both its read and write address. signal is issued is the data transferred to the command latch and acted on. I2C Sub-Addressed Writing I2C Bus Read Operation The LTC3375 has 13 command registers for control input. They are accessed by the I2C port via a sub-addressed writing system. The LTC3375 has 13 command registers and three status registers.
LTC3375 Operation RST MASK REGISTER VCC EXTERNAL PULL-UP RESISTOR AND1 REGULATOR 92.5% OF PROGRAMMED VOUT – + RST OTHER UNMASKED PGOOD OUTPUTS VOUT PGOOD COMPARATOR AND2 UNMASKED PGOOD OUTPUTS VCC EXTERNAL PULL-UP RESISTOR UNMASKED ERROR OTHER UNMASKED ERRORS IRQ SET CLRINT CLR IRQ STATUS REGISTER IRQ MASK REGISTER 3375 F04 Figure 4. Simplified Schematic RST and IRQ Signal Path An error condition that pulls the RST pin low is not latched.
LTC3375 Operation RESET_ALL Functionality Table 2. Die Temperature Warning Thresholds DT[1], DT[0] DIE TEMPERATURE WARNING THRESHOLD 00 (Default) Inactive 01 140°C 10 125°C 11 110°C A die temperature warning is reported to the user by pulling the IRQ pin low. This warning can be read back on the LSB of the Temp_Monitor register. The die temperature warning flag is disabled when the DT bits are set to 00 (default).
LTC3375 Operation After detecting an external clock on the first rising edge of the SYNC pin, the PLL starts up at the current frequency being programmed by the RT pin. The internal PLL then requires a certain number of periods to gradually settle until the frequency at SW matches the frequency and phase of SYNC. If the use of the VCC regulator is not desired, then VCC should be tied to an external DC voltage source and a decoupling capacitor. FBVCC and VSHNT should be tied to ground.
LTC3375 Applications Information Buck Switching Regulator Output Voltage and Feedback Network The output voltage of the buck switching regulators is programmed by a resistor divider connected from the switching regulator’s output to its feedback pin and is given by VOUT = VFB(1 + R2/R1) as shown in Figure 5. Typical values for R1 range from 40k to 1M.
LTC3375 Applications Information Table 4. Recommended Inductors for 2A Buck Regulators PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) XFL4020-102ME 1.0 5.1 11.9 4 × 4 × 2.1 74437324010 1 9 27 4.45 × 4.06 × 1.8 XAL4020-222ME 2.2 5.6 38.7 4 × 4 × 2.1 FDV0530-2R2M 2.2 5.3 15.5 6.2 × 5.8 × 3 IHLP2020BZER2R2M-11 2.2 5 37.7 5.49 × 5.18 × 2 XAL4030-332ME 3.3 5.5 28.6 4 × 4 × 3.1 FDV0530-3R3M 3.3 4.1 34.1 6.2 × 5.
LTC3375 Applications Information VCC Shunt Regulator If load steps seen on VCC are of great concern, then the compensation capacitor should be tied from VCC to ground as shown in Figure 6a. If load steps are not of a concern, but instead smaller compensation components are desired then the compensation capacitor should be tied from VSHNT to ground as shown in Figure 6b. 301k VSHNT VCC 1Ω 1.02M FBVCC 22µF 576k 1.2V + – 3375 F06a Figure 6a.
LTC3375 Applications Information In general the circuit in 6a is recommended if the application needs to drive any external circuitry with VCC or if the larger compensation capacitor is tolerable. If VCC is only needed to drive the LTC3375 and smaller component sizes are critical, then the circuit in Figure 6b may be used.
LTC3375 Applications Information Table 8. Global Control Program Register Bit Format Bit7 RESET_ALL Default is ‘0’. When asserted all buck converters will power down for 1 second after which the bit will clear itself. Bit6(DT1) Bit5(DT0) DT WARNING CONTROL Default is ‘00’ which deactivates the DT warning. ‘01’ programs –140°, ‘10’ programs –125°, and ‘11’ programs –110°. Bit4 IGNORE_EN Default is ‘0’ which allows the EN pins to power on the buck converters.
LTC3375 Typical Applications 3.3V TO 5.5V 2.2µH 10µF 3.3V 1A 22µF VIN1 VIN8 SW1 SW8 FB1 FB8 1.02M 649k 287k 3V TO 5.5V 10µF 22µF 22µF 1.8V 1A 10µF 1.5V 1A 10µF 1.2V 1A 10µF 1V 1A 10µF 432k 2.2µH 3V 1A 2.25V TO 5.5V 2.2µH VIN2 VIN7 SW2 SW7 FB2 FB7 2.25V TO 5.5V 2.2µH 1.07M 464k 340k 22µF 432k LTC3375 2.5V TO 5.5V 2.2µH 10µF 2.5V 1A 22µF VIN3 VIN6 SW3 SW6 FB3 FB6 1.02M 422k 412k 2.25V TO 5.5V 10µF 22µF VIN4 VIN5 SW4 SW5 2.25V TO 5.5V 2.
LTC3375 Typical Applications VIN 5.5V TO 60V CIN 22µF 100k INTVCC VIN INTVCC 2.2µF PGOOD PLLIN/MODE ILIM PGND D1 TG 470pF FREQ 34.8k 0.1µF ITH 2.2µH 1.2V 1A 22µF L1 8µH SW SENSE+ – TRACK/SS SENSE EXTVCC SGND VFB 2.5V 1A 22µF 5V 6A 100k MTOP, MBOT: Si7850DP L1 COILCRAFT SER1360-802KL COUT: SANYO 10TPE330M D1: DFLS1100 VIN1 VIN8 SW1 SW8 FB1 FB8 19.1k 10µF 2.2µH 422k 2.2µH COUT 330µF 1nF 422k 649k 10µF RSENSE 7mΩ MBOT BG SGND 10µF MTOP 0.1µF LTC3891 RUN BOOST 1.
LTC3375 Typical Applications 2.7V TO 5.5V 10µF 2.5V 4A 2.2µH 100µF 1.02M VIN1 VIN6 SW1 SW2 SW3 SW4 FB1 SW8 SW7 SW6 2.2µH 422k 68µF 1.2V 3A 10µF FB6 412k 649k 10µF VIN2 VIN7 FB2 FB7 10µF LTC3375 10µF 10µF VIN3 VIN8 FB3 FB8 VIN4 VIN5 SW5 10µF 2.2µH 511k FB4 22µF 1.6V 1A 10µF FB5 422k 1µF I2C CONTROL SCL SDA WDI EN1 EN5 EN6 KILL SYNC RT EN2 EN3 EN4 EN7 EN8 MICROPROCESSOR CONTROL VSHNT VCC IRQ RST WDO ON TEMP CT 0.
LTC3375 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UK Package 48-Lead Plastic QFN (7mm × 7mm) (Reference LTC DWG # 05-08-1704 Rev C) 0.70 ±0.05 5.15 ±0.05 5.50 REF 6.10 ±0.05 7.50 ±0.05 (4 SIDES) 5.15 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 7.00 ±0.10 (4 SIDES) 0.75 ±0.05 R = 0.10 TYP R = 0.115 TYP 47 48 0.40 ±0.
LTC3375 Revision History REV DATE DESCRIPTION A 03/13 Clarified VCC input supply current specification PAGE NUMBER Clarified RST pin functionality Clarified Buck Regulators with Combined Power Stages 4 12 16, 17 Clarified Table 6 Recommended Inductor Ratings 27 12 B 07/13 Modified SYNC pin description C 10/13 Changed units on VIL specification 5 Modified Bit 3 conditions in Global Control Program Register Bit Format Table 30 3375fc Information furnished by Linear Technology Corporation
LTC3375 Typical Application Combined Bucks with 3MHz Switch Frequency, Sequenced Power Up, and KILL Based Hardware Override Shut Down 2.25V TO 5.5V 10µF 10µF VIN1 VIN8 FB8 VIN2 VIN7 3.3V TO 5.5V 10µF 10µF FB2 VIN3 10µF 1µH SW7 FB3 SW8 1µH 1.8V 3A 68µF SW1 SW2 SW3 649k 287k FB1 1µH 1.2V 1A 22µF 2.5V TO 5.5V VIN6 FB6 LTC3375 VIN4 10µF 10µF VIN5 10µF 1µH SW5 SW4 SW6 422k FB4 1.02M HIGH VOLTAGE >4.0V 301k VSHNT SDA SCL WDI EN1 EN4 EN5 EN7 EN2 EN3 EN6 EN8 1.
