LTC3562EUD#TRPBF

LTC3562 I2C Quad Synchronous Step-Down DC/DC Regulator 2 × 600mA, 2 × 400mA DESCRIPTION FEATURES n n n n n n n n n Four Independent I2C Controllable Step-Down Regulators (2 × 600mA, 2 × 400mA) Two I2C Programmable Feedback Voltage Regulators (R600A, R400A): VFB 425mV to 800mV Two I2C Programmable Output Voltage Regulators (R600B, R400B): VOUT 600mV to 3.775V Programmable Modes: Pulse Skip, LDO, Burst Mode,® Forced Burst Mode Operation Quiescent Current < 100μA (All Regulators Enabled in LDO Mode) Fixed 2.25MHz Switching Frequency (Pulse Skip Mode) Slew Limiting Reduces Switching Noise Power-On Reset Output for Regulator R600A Small, Thermally Enhanced, 20-Lead 3mm × 3mm QFN Package The LTC®3562 is a quad high efficiency monolithic synchronous step-down regulator with an I2C interface. Two regulators are externally adjustable and can have their feedback voltages programmed between 425mV and 800mV in 25mV steps (Type A). The other two regulators are fixed output regulators whose output voltages can be programmed between 600mV and 3.775V in 25mV steps (Type B). All four regulators operate independently and can be put into pulse skip, LDO, Burst Mode operation, or forced Burst Mode operation through I2C control. The Type-A regulators have separate RUN pins that can be enabled if I2C control is unavailable. The 2.85V to 5.5V input voltage range makes the LTC3562 ideally suited for single Li-Ion battery-powered applications. At low output load conditions, the regulators can be switched into LDO, Burst Mode operation, or forced Burst Mode operation, extending battery life in portable systems. The quiescent current drops to under 100μA with all regulators in LDO mode, and under 0.1μA when all regulators are shut down. APPLICATIONS n n n n n n Miscellaneous Handheld Applications with Multiple Supply Rails Personal Information Appliances Wireless and DSL Modems Digital Still Cameras MP3 Players Portable Instruments Switching frequency is internally set to 2.25MHz, allowing the use of small surface mount inductors and capacitors. All regulators are internally compensated. The LTC3562 is available in a low profile 3mm × 3mm QFN package. L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION R600x Burst Mode Efficiency and Power Loss vs Load Current High Efficiency Quad Step-Down Converter with I2C MICROPROCESSOR + 10μF VOUT 400A 1.5V 400mA 4.7μH RUN400A SW400A 10μF 10pF SCL SDA DVCC 475k FB400A LTC3562 100k POR600A SW600A 3.3μH VOUT 600A 1.8V 600mA 634k FB600A 10pF RUN600A 499k 536k 90 80 10μF 4.7μH 10μF 3.3μH SW400B SW600B OUT400B PGND AGND OUT600B 3562 TA01 VOUT 600B 3.3V 10μF 600mA VOUT = 2.5V VOUT = 1.2V 70 1000 VOUT = 1.8V 60 100 50 10 40 30 20 VOUT 400B 1.2V 400mA 10000 VOUT = 3.3V VOUT = 1.2V, 1.8V, 2.5V 10 0 0.01 VOUT = 3.3V POWER LOSS (mW) VIN 100 SDA SCL DVCC POR EFFICIENCY (%) Li-Ion/Polymer 3.4V TO 4.2V 1 VIN = 3.8V 0.1 1 10 100 LOAD CURRENT (mA) 0.1 1000 3562 TA01b 3562fa 1 LTC3562 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) RUN400A RUN600A DVCC SCL SDA TOP VIEW 20 19 18 17 16 15 POR600A AGND 1 14 FB600A FB400A 2 13 OUT600B 21 OUT400B 3 12 SW600B SW400B 4 11 PGND 7 8 9 10 VIN VIN SW600A 6 VIN PGND 5 SW400A VIN ............................................................... –0.3V to 6V RUN600A ...................................... –0.3V to (VIN + 0.3V) RUN400A ...................................... –0.3V to (VIN + 0.3V) FBx ............................................................... –0.3V to 6V SWx ............................................................. –0.3V to 6V OUTx ............................................................ –0.3V to 6V DVCC , POR600A, SDA, SCL ......................... –0.3V to 6V ISW400x (DC) ........................................................600mA ISW600x (DC) ........................................................850mA Operating Temperature (Note 2)...............–40°C to 85°C Storage Temperature Range...................–65°C to 125°C Junction Temperature (Note 3) ............................. 125°C UD PACKAGE 20-LEAD (3mm × 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3562EUD#PBF LTC3562EUD#TRPBF LCPV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V, unless otherwise noted. PARAMETER CONDITIONS l VIN Input Voltage Range VIN Input Current (Per Regulator Enabled) VIN Shutdown Current MIN TYP 2.7 MAX UNITS 5.5 V Pulse Skip Mode, IOUT = 0 Burst Mode Operation, IOUT = 0 Forced Burst Mode Operation, IOUT = 0 LDO Mode, IOUT = 0 Shutdown Mode, IOUT = 0, DVCC = 1.8V 220 35 25 24 0.7 60 40 40 3 μA μA μA μA μA All Regulators in Shutdown, DVCC = 0V 0.1 1 μA RUN600A, RUN400A Input High Threshold l RUN600A, RUN400A Input Low Threshold l 1.0 V 0.3 V RUN600A, RUN400A Input High Current RUNx = VIN –1 1 μA RUN600A, RUN400A Input Low Current RUNx = 0V –1 1 μA POR600A Threshold Percentage of R600A’s Final Output Voltage –8 POR600A On-Resistance 16 POR600A Delay 231 % 40 Ω ms 3562fa 2 LTC3562 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS I2C Port l DVCC Operating Voltage DVCC Operating Current 1.5 DVCC = 1.8V, Serial Port Idle DVCC UVLO Threshold Voltage V 1 μA 1 VIL SDA, SCL (Low Level Input Voltage) V 0.3 • DVCC VIH SDA, SCL (High Level Input Voltage) VOL SDA (Digital Output Low) 5.5 0.7 • DVCC IPULLUP = 3mA V V 0.08 V Serial Port Timing (Note 4) tSCL Clock Operating Frequency tBUF Bus Free Time Between Stop and Start Conditions 1.3 400 kHz μs tHD,STA Hold Time After (Repeated) Start Condition 0.6 μs tSU,STA Repeated Start Condition Setup Time 0.6 μs tSU,STO Stop Condition Setup Time 0.6 μs tHD,DAT(OUT) Data Hold Time 225 tHD,DAT(IN) Input Data Hold Time tSU,DAT Data Setup Time 100 ns tLOW Clock Low Period 1.3 μs tHIGH Clock High Period 0.6 μs tf Clock Data Fall Time 20 300 ns tr Clock Data Rise Time 20 300 ns tSP Spike Suppression Time 50 ns 0 900 ns ns BUCK DC/DC ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V, VOUTx = 1.5V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 1.91 2.25 2.59 MHz Regulators R600A, R400A, R600B, R400B fOSC Maximum Duty Cycle Pulse Skip Mode LDO Mode Closed Loop ROUT LDO Mode 100 % Ω 0.25 Regulators R600A, R600B PMOS Switch Current Limit Pulse Skip Mode 850 1200 0.38 PMOS RDS(ON) NMOS RDS(ON) LDO Mode Open Loop ROUT LDO Mode Available Output Current Forced Burst Mode LDO, VOUT = 1.2V SW Pull-Down in Shutdown Shutdown 75 50 1500 mA Ω 0.38 Ω 2.2 Ω 140 mA mA 2.5 kΩ 3562fa 3 LTC3562 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V, VOUTx = 1.5V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Pulse Skip Mode 600 800 1000 mA Regulators R400A, R400B PMOS Switch Current Limit PMOS RDS(ON) 0.5 Ω NMOS RDS(ON) 0.5 Ω 3 Ω LDO Mode Open Loop ROUT LDO Mode SW Pull-Down in Shutdown Shutdown Available Output Current Forced Burst Mode LDO Mode, VOUT = 1.2V 2.5 kΩ 50 50 100 mA mA Regulators R600A, R400A VFB(MAX) DAC = XXX1111, Pulse Skip Mode l 0.776 0.800 0.824 V VFB(MIN) DAC = XXX0000, Pulse Skip Mode l 0.412 0.425 0.438 V VFB(STEP) (0 to 15) IFB 25 FB Input Current DAC = XXX1111 mV –50 0 50 nA Regulators R600B, R400B VOUT(MIN) VIN = 4V, DAC = 0000000, Pulse Skip Mode l 0.582 0.600 0.618 V VOUT(MAX) VIN = 4V, DAC = 1111111, Pulse Skip Mode l 3.661 3.775 3.889 V VOUT(STEP) (0 to 127) VIN = 4V 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 LTC3562E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process control. 25 mV Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Overtemperature protection is active when junction temperature exceeds the maximum operating junction temperature. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 4: The serial port is tested at rated operating frequency. Timing parameters are tested and/or guaranteed by design. 3562fa 4 LTC3562 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current FORCED Burst Mode OPERATION 80 Burst Mode 70 OPERATION 600mA BUCKS 50 40 PULSE SKIP 60 20 VIN = 3.8V VOUT = 1.2V 1 10 IOUT (mA) 100 Burst Mode OPERATION 40 20 10 PULSE SKIP 50 30 0.1 80 600mA BUCKS 70 30 0 0.01 100 VIN = 3.8V VOUT = 1.8V EFFICIENCY (%) EFFICIENCY (%) 600mA BUCKS PULSE SKIP Burst Mode OPERATION 40 0.1 1 10 IOUT (mA) 100 1 10 IOUT (mA) 100 1000 100 VOUT = 1.2V 80 70 70 60 50 40 20 0.1 0.1 1 10 IOUT (mA) 100 0 2.5 3 4 4.5 3.5 INPUT VOLTAGE (V) VOUT = 1.8V 60 50 40 30 IOUT = 0.1mA IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 400mA 10 1000 Efficiency vs Input Voltage Burst Mode Operation 80 30 VIN = 3.8V VOUT = 3.3V VIN = 3.8V VOUT = 2.5V 3562 G03 90 30 0 0.01 0 0.01 1000 90 20 10 40 10 EFFICIENCY (%) FORCED Burst Mode 90 OPERATION 50 Burst Mode OPERATION Efficiency vs Input Voltage Burst Mode Operation 100 60 PULSE SKIP 50 3562 G02 Efficiency vs Load Current 70 60 30 3562 G01 80 600mA BUCKS 70 20 10 1000 FORCED Burst Mode OPERATION 90 80 60 0 0.01 Efficiency vs Load Current 100 FORCED Burst Mode OPERATION 90 EFFICIENCY (%) 90 EFFICIENCY (%) Efficiency vs Load Current 100 EFFICIENCY (%) 100 IOUT = 0.1mA IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 400mA 20 10 0 5 5.5 2.5 3 4 4.5 3.5 INPUT VOLTAGE (V) 5 5.5 3562 G04 3562 G06 3562 G05 Output Transient Burst Mode Operation Output Transient Pulse Skip Mode VOUT400B 50mV/DIV AC COUPLED VOUT400B 50mV/DIV AC COUPLED VOUT400A 50mV/DIV AC COUPLED VOUT600B 50mV/DIV AC COUPLED 300mA IOUT400B 5mA VOUT600A 500mV/DIV INDUCTOR CURRENT IL = 100mA/ DIV 300mA IOUT400B 5mA 50μs/DIV VOUT400B = 1.2V VOUT400A = 1.2V IOUT400A = 20mA Start-Up Transient Pulse Skip Mode RUN600A OFF 2V/DIV ON 3562 G07 50μs/DIV VOUT400B = 1.8V VOUT600B = 1.2V IOUT600B = 15mA 3562 G08 50μs/DIV 3562 G09 VOUT600A = 1.2V RLOAD = 6Ω 3562fa 5 LTC3562 TYPICAL PERFORMANCE CHARACTERISTICS R600A Feedback Voltage vs Temperature Output Voltage vs Load Current (B Version) 1.220 2.5 0.808 2.4 VIN = 5.5V 0.806 2.3 VIN = 3V 0.804 2.2 0.802 0.800 0.798 0.796 VIN = 3.8V VIN = 2.7V 2.1 2.0 1.9 0.794 1.7 1.6 0.790 –50 –25 25 50 0 TEMPERATURE (°C) 75 1.190 –25 25 50 0 TEMPERATURE (°C) 75 6 IOUT = 0mA VOUT = 1.2V Burst Mode Operation IOUT = 0mA CURRENT (mA) 35 30 FORCED Burst Mode OPERATION CONTINUOUS OPERATION 5 Burst Mode OPERATION 4 3 2 VOUT600A 50mV/DIV AC COUPLED SW 2V/DIV INDUCTOR CURRENT IL = 100mA/ DIV 1 LDO MODE 0 20 2.7 3.1 3.5 3.9 4.3 4.7 VIN VOLTAGE (V) 5.1 4.5 3.5 4 VOLTAGE (V) 400mA – VOUT = 1.2V 600mA – VOUT = 1.2V 400mA – VOUT = 1.8V 600mA – VOUT = 1.8V 3562 G13 2.5 5 3 5.5 PVIN = 3.8V LOAD = 50mA 6 3562 G14 400mA – VOUT = 2.5V 600mA – VOUT = 2.5V 400mA – VOUT = 3.3V 600mA – VOUT = 3.3V Output Voltage vs Load Current Forced Burst Mode Operation VOUT600A 50mV/DIV AC COUPLED Switch RDS(ON) vs Input Voltage 700 1.22 FORCED Burst Mode OPERATION 1.20 600 400mA PMOS SWITCH RDS(ON) (Ω) 1.21 VOLTAGE (V) 1.19 INDUCTOR CURRENT IL = 150mA/ DIV 1.18 1.17 LDO MODE 1.16 1.15 2μs/DIV PVIN = 3.8V LOAD = 50mA 3562 G16 3562 G15 2μs/DIV PULSE SKIP OPERATION 2 5.5 SW 2V/DIV 600 500 3562 G12 Dynamic Supply Current vs Input Voltage 40 IIN (μA) 300 400 200 LOAD CURRENT (mA) 3562 G11 Dynamic Supply Current vs Input Voltage 25 100 0 100 3562 G10 45 PULSE SKIP 1.205 1.195 1.5 –50 100 1.210 1.200 1.8 0.792 VIN = 3.8V VOUT = 1.2V (TYPE-B) 1.215 VOLTAGE (V) IOUT = 1mA fOSC (MHz) VOLTAGE (mV) 0.810 Oscillator Frequency vs Temperature 400mA NMOS 600mA PMOS 500 400 600mA NMOS 300 200 1.14 100 VIN = 3.8V VOUT = 1.2V (TYPE-B) 1.13 1.12 0 20 60 80 100 40 LOAD CURRENT (mA) 0 120 140 3562 G17 2.7 3.1 3.5 3.9 4.3 4.7 VIN VOLTAGE (V) 5.1 5.5 3562 G18 3562fa 6 LTC3562 PIN FUNCTIONS AGND (Pin 1): Analog Ground Pin. All small-signal components should connect to this ground, which in turn connects to PGND at one point. FB400A (Pin 2): Feedback Pin for R400A. When the control loop is complete, this pin servos to 1 of 16 possible set-points based on the programmed value from the I2C serial port (see Table 4). OUT400B (Pin 3): Output Voltage Feedback Pin for R400B. An I2C programmable internal resistor divider divides the output voltage down for comparison to the internal reference voltage. This pin converges to 1 of 128 possible set-points based on the programmed value from the I2C serial port (see Tables 5 and 6). This node must be bypassed to GND with a 10μF or greater ceramic capacitor. SW400B (Pin 4): Switch Node Connection to the Inductor for R400B. This pin connects to the drains of the internal power MOSFET switches of R400B. PGND (Pins 5, 11): Power Ground Pin. Connect this pin closely to the (–) terminal of CIN. SW400A (Pin 6): Switch Node Connection to the Inductor for R400A. This pin connects to the drains of the internal power MOSFET switches of R400A. VIN (Pins 7, 8, 9): Input Supply Pin. This pin must be closely decoupled to GND with a 10μF or greater ceramic capacitor. SW600A (Pin 10): Switch Node Connection to the Inductor for R600A. This pin connects to the drains of the internal power MOSFET switches of R600A. SW600B (Pin 12): Switch Node Connection to the Inductor for R600B. This pin connects to the drains of the internal power MOSFET switches of R600B. OUT600B (Pin 13): Output Voltage Feedback Pin for R600B. An I2C programmable internal resistor divider divides the output voltage down for comparison to the internal reference voltage. This pin converges to 1 of 128 possible set-points based on the programmed value from the I2C serial port (see Tables 5 and 6). This node must be bypassed to GND with a 10μF or greater ceramic capacitor. FB600A (Pin 14): Feedback Pin for R600A. When the control loop is complete, this pin servos to 1 of 16 possible set-points based on the programmed value from the I2C serial port (see Table 4). POR600A (Pin 15): Power-On Reset for R600A. This opendrain output goes high impedance after a 230ms delay after the output of R600A reaches 92% of its regulation voltage. This output gets pulled to GND whenever R600A falls below 92% of its regulation voltage. RUN400A (Pin 16): Enable Pin for R400A, Active High. Apply a voltage greater than 1V to enable this regulator. RUN600A (Pin 17): Enable Pin for R600A, Active Low. Apply a voltage less than 0.3V to enable this regulator. DVCC (Pin 18): Supply Voltage for I2C Lines. This pin sets the logic reference level of the LTC3562. A UVLO circuit on the DVCC pin forces all registers to a default setting whenever DVCC is < 1V. Bypass to GND with a 0.1μF capacitor. SCL (Pin 19): I2C Clock Input. Serial data is shifted one bit per clock to control the LTC3562. The logic level for SCL is referenced to DVCC. SDA (Pin 20): I2C Data Input. The logic level for SDA is referenced to DVCC. Exposed Pad (Pin 21): Ground. Must be soldered to PCB ground for electrical contact and optimum thermal performance. 3562fa 7 LTC3562 BLOCK DIAGRAM 17 18 20 19 DVCC SDA SCL DVCC SDA 16 RUN600A I 2C EN 1 SCL MODE DATA 2 VIN 7, 8, 9 RUN400A 4 1 R600A 7 4 D/A REF600A EN 0.425V-0.8V SW600A 10 REF MODE FB FB600A 14 R400A 4 D/A REF400A EN 0.425V-0.8V SW400A MODE FB FB400A 1 6 REF 2 R600B AGND 1 EN 0.6V SW600B 12 REF OUT600B MODE 13 FB 7 R400B 1 EN 0.6V SW400B OUT400B MODE 15 POR600A 4 REF 3 FB 7 230ms Delay POWER GOOD R600A PGND 5,11 3562 BD 3562fa 8 LTC3562 OPERATION Introduction The LTC3562 is a highly integrated power management IC that contains four I2C controllable, monolithic, high efficiency step-down regulators. Two regulators provide up to 600mA of output current and the other two regulators produce up to 400mA. All four regulators are 2.25MHz, constant-frequency, current mode switching regulators that can be independently controlled through I2C. All regulators are internally compensated eliminating the need for external compensation components. The LTC3562 offers two different types of adjustable step-down regulators. The two Type-A regulators (R600A, R400A) can have the feedback voltages adjusted through I2C from 425mV to 800mV in 25mV increments. The two Type-B regulators (R600B, R400B) can have the output voltages adjusted through I2C control from 600mV to 3.775V in 25mV increments. All four converters support 100% duty cycle operation (low dropout mode) when their input voltage drops very close to their output voltage. To suit a variety of applications, four selectable mode functions are available on the LTC3562’s step-down regulators to trade-off noise for efficiency. At moderate to heavy loads, the constant-frequency pulse skip mode provides the lowest output switching noise solution. At lighter loads, either Burst Mode operation, forced Burst Mode operation or LDO mode may be selected to optimize efficiency. The switching regulators also include soft-start to limit inrush current when powering on, shortcircuit current protection, and switch node slew limiting circuitry to reduce radiated EMI. No external compensation components are required. VFB Adjustable (Type-A) Regulators The two Type-A step-down regulators (R600A and R400A) have individual programmable feedback servo voltages via I2C control. Given a particular feedback servo voltage, the output voltage is programmed using a resistor divider from the switching regulator output connected to the feedback pins (Figure 1). The output voltage is related to the feedback servo voltage by the following equation:
R1  VOUTxA = VFBxA  + 1  R2  Through I2C control, VFBxA can be programmed from 800mV (full scale) down to 425mV in 25mV increments. When the RUN pins (RUN600A and RUN400A) are used to activate these regulators, the default feedback servo voltage is set to 800mV. LTC3562 L SWxA CFB R1 CO FBxA 425mV to 800mV R2 GND 3562 F01 Figure 1. Type-A Regulator Application Circuit Typical values for R2 are in the range of 40k to 1MΩ. The capacitor CFB cancels the pole created by the feedback resistors and the input capacitance of the FB pin and also helps to improve transient response for output voltages much greater than 0.8V. A variety of capacitor sizes can be used for CFB but a value of 10pF is recommended for most applications. Experimentation with capacitor sizes between 2pF and 22pF may yield improved transient response. Regulators R600A and R400A have individual RUN pins that can enable the regulators without accessing the I2C port. The RUN600A and RUN400A pins are OR’ed with the enable signals coming from the I2C port (refer to the Block Diagram) such that regulators R600A and R400A can be enabled if the I2C port is unavailable. The RUN600A pin is active low and the RUN400A pin is active high. When the RUN pins are activated, the Type-A regulators are enabled in a default setting. The default mode for the regulators is pulse skip mode and the default feedback servo voltage setting is 800mV. Once enabled with these default settings, the settings can always be changed on the fly through I2C once the I2C terminal is available. The maximum operating output current of regulators R600A and R400A are 600mA and 400mA, respectively. 3562fa 9 LTC3562 OPERATION VOUT Adjustable (Type-B) Regulators Unlike the Type-A regulators, the two Type-B regulators do not require an external resistor divider network to program its output voltage. Regulators R600B and R400B have feedback resistor networks internal to the chip whose values can be adjusted through I2C control. These internal feedback resistors can be configured such that the output voltages can be programmed directly. The output voltages can be programmed from 600mV to 3.775V in 25mV increments. Pins OUT600B and OUT400B are feedback sense pins that connect to the top of the internal resistor divider networks. These output pins should sense the output voltages of the regulators right at the output capacitor CO (after the inductor), as illustrated in Figure 2. The maximum operating current for regulators R600B and R400B are 600mA and 400mA, respectively. The Type-B regulators do not have individual run pins as do the Type-A regulators. Thus regulators R600B and R400B can only be enabled through control of the I2C port. When the part initially powers up, the Type-B regulators default to shutdown mode and remain disabled until programmed through I2C. Regulator Operating Modes All of the LTC3562’s switching regulators include four possible operating modes to meet the noise/power needs of a variety of applications. In pulse skip mode, an internal latch is set at the start of every cycle which turns on the main P-channel MOSFET switch. During each cycle, a current comparator compares the peak inductor current to the output of an error amplifier. The output of the current comparator resets the internal latch which causes the main P-channel MOSFET switch to turn off and the N-channel MOSFET synchronous rectifier to turn on. The N-channel MOSFET synchronous rectifier turns off at the end of the 2.25MHz cycle or if the current through the N-channel MOSFET synchronous rectifier drops to zero. Using this method of operation, the error amplifier adjusts the peak inductor current to deliver the required output power. All necessary compensation is internal to the switching regulator requiring only a single ceramic output capacitor for stability. At light loads in pulse skip mode, the inductor current may reach zero on each pulse which will turn off the N-channel MOSFET synchronous rectifier. In this case, the switch node (SW) goes high impedance and the switch node voltage will “ring.” This is discontinuous mode operation, and is normal behavior for a switching regulator. At very light loads in pulse skip mode, the switching regulators will automatically skip pulses as needed to maintain output regulation. At high duty cycle (VOUT > VIN/2) it is possible for the inductor current to reverse at light loads, causing the step-down switching regulator to operate continuously. When operating continuously, regulation and low noise output voltage are maintained, but input operating current will increase to a couple mA. In forced Burst Mode operation, the switching regulators use a constant-current algorithm to control the inductor current. By controlling the inductor current directly and using a hysteretic control loop, both noise and switching losses are minimized. In this mode output power is limited. While operating in forced Burst Mode operation, LTC3562 L 600mV to 3.775V SWxB CO OUTxB GND 3562 F02 Figure 2. Type-B Regular Application Circuit 3562fa 10 LTC3562 OPERATION the output capacitor is charged to a voltage slightly higher than the regulation point. The step-down converter then goes into sleep mode, during which the output capacitor provides the load current. In sleep mode, most of the regulator’s circuitry is powered down, helping conserve battery power and increase efficiency. When the output voltage drops below a predetermined value, the switching regulator circuitry is powered on and another burst cycle begins. The duration for which the regulator operates in sleep mode depends on the load current. The sleep time decreases as the load current increases. Forced Burst Mode operation has a maximum deliverable output current of about 140mA for the 600mA regulators and 100mA for the 400mA regulators. Beyond the maximum deliverable output current, the step-down switching regulator will not enter sleep mode and the output will drop out of regulation. Forced Burst Mode operation provides a significant improvement in efficiency at light loads at the expense of higher output ripple when compared to pulse skip mode. For many noise-sensitive systems, forced Burst Mode operation might be undesirable at certain times (i.e., during a transmit or receive cycle of a wireless device), but highly desirable at others (i.e., when the device is in low power standby mode). The I2C port can be used to enable or disable forced Burst Mode operation at any time, offering both low noise and low power operation when they are needed. In Burst Mode operation, the switching regulator automatically switches between fixed frequency pulse skip operation and hysteretic control as a function of the load current. At light loads the regulators operate in hysteretic mode and at heavy loads they operate in constant-frequency mode. The constant-frequency mode provides the same output ripple and efficiency as pulse skip mode while hysteretic mode provides slightly lower output ripple than forced Burst Mode operation at the expense of slightly lower efficiency. Finally, the switching regulators have an LDO mode that gives a DC option for regulating their output voltages. In LDO mode, the switching regulators are converted to linear regulators and deliver continuous power from their SWx pins through their respective inductors. This mode gives the lowest possible output noise as well as low quiescent current at light loads. Dropout Operation It is possible for VIN to approach a switching regulator’s programmed output voltage (e.g., a battery voltage of 3.4V with a programmed output voltage of 3.3V). When this happens, the PMOS switch duty cycle increases until it is turned on continuously at 100%. In this dropout condition, the respective output voltage equals the regulator’s input voltage minus the voltage drops across the internal P-channel MOSFET and the inductor. Soft-Start Operation Soft-start is accomplished by gradually increasing the peak inductor current for each switching regulator over a 500μs period. This allows each output to rise slowly, helping minimize the battery in-rush current. A softstart cycle occurs whenever a given switching regulator is enabled, or after a fault condition has occurred (thermal shutdown). A soft-start cycle is not triggered by changing operating modes. This allows seamless output operation when transitioning between Burst Mode operation, forced Burst Mode operation, pulse skip mode or LDO mode. Switching Slew Rate Control The step-down switching regulators contain new patent pending circuitry to limit the slew rate of the switch node (SWx). This new circuitry is designed to transition the switch node over a period of a couple nanoseconds, significantly reducing radiated EMI and conducted supply noise, while keeping efficiency high. Step-Down Switching Regulator in Shutdown The step-down switching regulators are in shutdown when not enabled for operation. In shutdown, all circuitry in the step-down switching regulator is disconnected from the switching regulator input supply, leaving only a few nano-amps of leakage current. The step-down switching regulator outputs are individually pulled to ground through a 2k resistor on the switch pin (SWx) when in shutdown. 3562fa 11 LTC3562 OPERATION I2C Interface Acknowledge The LTC3562 may communicate with a host (master) using the standard I2C 2-wire interface. The Timing Diagram in Figure 4 shows the timing relationship of the signals on the bus. The two bus lines, SDA and SCL, must be high when the bus is not in use. External pull-up resistors or current sources, such as the LTC1694 SMBus Accelerator, are required on these lines. The LTC3562 is a receive-only (slave) device. The I2C control signals, SDA and SCL are scaled internally to the DVCC supply. DVCC should be connected to the same power supply as the microcontroller generating the I2C signals. The Acknowledge signal is used for handshaking between the master and the slave. An Acknowledge (active LOW) generated by the slave (LTC3562) lets the master know that the latest byte of information was received. The Acknowledge-related clock pulse is generated by the master. The master releases the SDA line (HIGH) during the Acknowledge clock cycle. The slave-receiver must pull down the SDA line during the Acknowledge clock pulse so that it remains a stable low during the high period of this clock pulse. The I2C port has an undervoltage lockout on the DVCC pin. When DVCC is below approximately 1V, the I2C serial port is cleared and the two switching Type-A regulators are set to full scale. Slave Address Byte Bus Speed The I2C port is designed to be operated at speeds of up to 400kHz. It has built-in timing delays to ensure correct operation when addressed from an I2C compliant master device. It also contains input filters designed to suppress glitches should the bus become corrupted. START and STOP Conditions A bus master signals the beginning of a communication to a slave device by transmitting a start condition. A start condition is generated by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it issues a stop condition by transitioning SDA from low to high while SCL is high. The bus is then free for communication with another I2C device. Byte Format Each byte sent to the LTC3562 must be 8 bits long followed by an extra clock cycle for the Acknowledge bit to be returned by the LTC3562. The data should be sent to the LTC3562 most significant bit (MSB) first. The LTC3562 responds to only one 7-bit address which has been factory programmed to 11001010. The eighth bit of the address byte (R/W) must be 0 for the LTC3562 to recognize the address since it is a write-only device. This effectively forces the address to be 8 bits long where the least significant bit of the address is 0. If the correct 7-bit address is given but the R/W bit is 1, the LTC3562 will not respond. Sub-Address Byte The sub-address byte uses bits A7 through A4 to specify the regulator(s) being programmed by that particular three-byte sequence (refer to Table 2). A specific regulator gets programmed if its corresponding sub-address bit is high, whereas the regulator ignores the 3-byte sequence if its sub-address bit is low. Note that multiple regulators can be programmed by the same 3-byte sequence if more than one of the sub-address bits are high. Bits A1 and A0 of the sub-address byte are used to program the operating mode (Table 3). Bits A3 and A2 of the sub-address byte are not used. Data Byte The data byte only affects the regulators that are specified to be programmed by the sub-address byte. The MSB of the data byte (B7) is used to enable or disable the regulator(s) being programmed. A high B7 indicates an enable command, whereas a low B7 indicates a shutdown command. 3562fa 12 LTC3562 OPERATION SUB-ADDRESS ADDRESS DATA BYTE WR 1 1 0 0 1 0 1 0 SDA 1 1 0 0 1 0 1 0 SCL 1 2 3 4 5 6 7 8 A7 A6 A5 A4 A3 A2 A1 A0 B7 B6 B5 B4 B3 B2 B1 B0 ACK A7 A6 A5 A4 A3 A2 A1 A0 ACK 7 6 5 4 3 2 1 0 ACK 9 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 START STOP 9 3562 F03 Figure 3. Bit Assignments SDA tSU, STA tSU, DAT tLOW tBUF tSU, STO tHD, STA tHD, DAT 3562 F04 SCL tHIGH tHD, STA START CONDITION tSP REPEATED START CONDITION tf tr STOP CONDITION START CONDITION Figure 4. Timing Parameters Table 1. Write Word Protocol Used by the LTC3562 1 7 1 1 8 1 8 1 1 S Slave Address WR A *Sub-Address A Data Byte A P** S = Start Condition, WR = Write Bit = 0, A = Acknowledge, P = Stop Condition * The sub-address uses only the first four most significant bits, A7, A6, A5, and A4, for sub-addressing. The two least significant bits, A1 and A0, are used to program the regulator operating mode. **Stop can be delayed until all of the data registers have been written. Table 2. Sub-Address and Data Byte Mapping SUB-ADDRESS BYTE A7 A6 A5 A4 PROGRAM R600A PROGRAM R400A PROGRAM R600B PROGRAM R400B DATA BYTE A3 A2 NOT USED A1 A0 B7 ENABLE REGULATOR OPERATING REGULATOR MODE (SEE TABLE 3) B6 B5 B4 B3 B2 B1 B0 DAC CODE (See Tables 4, 5 and 6) 3562fa 13 LTC3562 OPERATION If a Type-A regulator is being programmed, then bits B3 through B0 program the DAC that controls the regulator’s feedback servo voltage. This 4-bit sequence programs the feedback voltage from 425mV to 800mV in 25mV increments (Table 4). Bits B6 through B4 are not used when programming a Type-A regulator. will ignore this stop condition and will not respond until a new start condition, correct address, new set of data and stop condition are transmitted. If a Type-B regulator is being programmed, then bits B6 through B0 program the DAC that controls the regulator’s output voltage. This 7-bit sequence programs the output voltage from 600mV to 3.775V in 25mV increments (Tables 5 and 6). Likewise, with only one exception, if the LTC3562 was previously addressed and sent valid data but not updated with a Stop, it will respond to any Stop that appears on the bus, independent of the number of Repeat-Starts that have occurred. If a Repeat-Start is given and the LTC3562 successfully acknowledges its address, it will not respond to a Stop until all three bytes of the new data have been received and acknowledged. Bus Write Operation I2C Examples The master initiates communication with the LTC3562 with a start condition and a 7-bit address followed by the write bit R/W = 0. If the address matches that of the LTC3562, the LTC3562 returns an Acknowledge. The master should then deliver the sub-address byte for the regulator(s) being programmed. Again the LTC3562 acknowledges and then the data byte is delivered starting with the most significant bit. The data byte and the two mode bits in the sub-address byte are transferred to an internal holding latch for each programmed regulator upon the return of an Acknowledge. After the sub-address byte and data byte have been transferred to the LTC3562, the master may terminate the communication with a stop condition. Alternatively, a repeat-start condition can be initiated by the master and the entire sequence can be repeated, this time accessing a different sub-address code to program another regulator. Likewise, the master can also initiate a Repeat-Start so that another chip on the I2C bus can be addressed. This cycle can continue indefinitely and the LTC3562’s regulators will remember the last input of valid data that it received. Once all chips on the bus have been addressed and sent valid data, a global stop condition can be sent and the LTC3562 will update its regulators with the data that it had received. To program R600A in forced Burst Mode operation with its feedback servo voltage set to 600mV: In certain circumstances the data on the I2C bus may become corrupted. In these cases the LTC3562 responds appropriately by preserving only the last set of complete data that it has received. For example, assume the LTC3562 has been successfully addressed and is receiving data when a stop condition mistakenly occurs. The LTC3562 Sub-Address Byte – 1000XX10 Data Byte – 1XXX0111 To program R600B and R400B in LDO mode with their output voltages set to 1.250V: Sub-Address Byte – 0011XX01 Data Byte – 10011010 To put the entire chip in shutdown and disable all regulators: Sub-Address Byte – 1111XXXX Data Byte – 0XXXXXXX Disabling the I2C Port The I2C serial port can be disabled by grounding the DVCC pin. In this mode, regulators R600A and R400A can only be activated through the individual logic input pins RUN600A and RUN400A. Disabling the I2C port also resets the feedback servo voltages to the default setting of 0.8V. Note that if the I2C port gets disabled while a Type-A regulator is enabled and its RUN pin is activated, the regulator will remain enabled and its feedback voltage will immediately be reset to the default setting of 0.8V. If the I2C port gets disabled and the RUN pins are not activated, then the regulators will immediately go into shutdown mode. Since regulators R600B and R400B do not have RUN pins, they immediately go into shutdown once the I2C port gets disabled. 3562fa 14 LTC3562 OPERATION Table 5. Type-B Regulator Base Output Voltage Programming Table 3. Regulator Operating Modes A1 A0 B6 B5 B4 B3 B2 TYPE-B REGULATOR BASE OUTPUT VOLTAGE 0 0 0 0 0 0.600 0 0 0 0 1 0.700 0 0 0 1 0 0.800 0 0 0 1 1 0.900 0 0 1 0 0 1.000 0 0 1 0 1 1.100 0 0 1 1 0 1.200 REGULATOR MODE 0 0 Pulse Skip Mode 0 1 LDO Mode 1 0 Forced Burst Mode Operation 1 1 Burst Mode Operation Table 4. Type-A Regulator Servo Voltage Programming B3 B2 B1 B0 TYPE-A REGULATOR SERVO (FEEDBACK) VOLTAGE 0 0 0 0 0.425 0 0 1 1 1 1.300 1 0 0 0 1.400 0 0 0 1 0.450 0 0 0 1 0 0.475 0 1 0 0 1 1.500 0 0 1 1 0.500 0 1 0 1 0 1.600 1 0 1 1 1.700 0 1 0 0 0.525 0 0 1 0 1 0.550 0 1 1 0 0 1.800 0 1 1 0 0.575 0 1 1 0 1 1.900 0 1 1 1 0.600 0 1 1 1 0 2.000 1 1 1 1 2.100 1 0 0 0 0.625 0 1 0 0 1 0.650 1 0 0 0 0 2.200 1 0 1 0 0.675 1 0 0 0 1 2.300 1 0 1 1 0.700 1 0 0 1 0 2.400 0 0 1 1 2.500 1 1 0 0 0.725 1 1 1 0 1 0.750 1 0 1 0 0 2.600 1 1 1 0 0.775 1 0 1 0 1 2.700 1 1 1 1 0.800 1 0 1 1 0 2.800 1 0 1 1 1 2.900 1 1 0 0 0 3.000 1 1 0 0 1 3.100 1 1 0 1 0 3.200 1 1 0 1 1 3.300 1 1 1 0 0 3.400 1 1 1 0 1 3.500 1 1 1 1 0 3.600 1 1 1 1 1 3.700 POR600A Pin The POR600A pin is an open-drain output used to indicate that regulator R600A has been enabled and has reached its final voltage. POR600A remains low impedance until regulator R600A reaches 92% of its regulation value. A 230ms delay is included to allow a system microcontroller ample time to reset itself. POR600A may be used as a power on reset to the microprocessor powered by regulator R600A or may be used to enable regulator R400A for supply sequencing. POR600A is an open drain output and requires a pull-up resistor to the output voltage of regulator R600A or another appropriate power source. Table 6. Type-B Regulator Incremental Output Voltage Programming B1 B0 TYPE-B REGULATOR INCREMENTAL OUTPUT VOLTAGE 0 0 +0.000 0 1 +0.025 1 0 +0.050 1 1 +0.075 3562fa 15 LTC3562 APPLICATIONS INFORMATION Inductor Selection Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. The step-down converters are designed to work with inductors in the range of 2.2μH to 10μH. For most applications a 4.7μH inductor is suggested for the lower power switching regulators R400A and R400B and 3.3μH is recommended for the more powerful switching regulators R600A and R600B. Larger value inductors reduce ripple current which improves output ripple voltage. Lower value inductors result in higher ripple current and improved transient response time, but will reduce the available output current. To maximize efficiency, choose an inductor with a low DC resistance. For a 1.2V output, efficiency is reduced about 2% for 100mΩ series resist-ance at 400mA load current, and about 2% for 300mΩ series resistance at 100mA load current. Choose an inductor with a DC current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current specified for the step-down converters. Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or Permalloy™ materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher core and DCR losses, and will not give the best efficiency. The choice of which style inductor to use often depends more on the price versus size, performance, and any radiated EMI requirements than on what the LTC3562 requires to operate. The inductor value also has an effect on Burst Mode and forced Burst Mode operations. Lower inductor values will cause the Burst Mode and forced Burst Mode switching frequencies to increase. Table 7 shows several inductors that work well with the LTC3562’s general purpose regulators. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors. Table 7. Recommended Inductors INDUCTOR L TYPE (μH) MAX IDC (A) MAX DCR (Ω) SIZE (mm) (L × W × H) 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 1.07 1.20 0.79 0.90 1.15 1.37 1.25 1.45 0.1 0.07 0.24 0.20 0.13* 0.105* 0.072* 0.052* 3.8 × 3.8 × 1.8 3.8 × 3.8 × 1.8 3.6 × 3.6 × 1.2 3.6 × 3.6 × 1.2 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.8 3.0 × 2.8 × 1.8 Toko www.toko.com CDRH3D16 4.7 3.3 CDRH2D11 4.7 3.3 CLS4D09 4.7 0.9 1.1 0.5 0.6 0.75 0.11 0.085 0.17 0.123 0.19 4 × 4 × 1.8 4 × 4 × 1.8 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 4.9 × 4.9 × 1 Sumida www.sumida.com 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 1.3 1.59 0.8 0.97 1.29 1.42 1.08 1.31 0.162 0.113 0.246 0.165 0.117* 0.104* 0.153* 0.108* 3.1 × 3.1 × 1.8 Cooper 3.1 × 3.1 × 1.8 www.cooperet.com 3.1 × 3.1 × 1.2 3.1 × 3.1 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.0 5.2 × 5.2 × 1.0 4.7 3.3 1.1 1.3 0.2 0.13 3.0 × 3.0 × 1.5 Coil Craft 3.0 × 3.0 × 1.5 www.coilcraft.com DB318C D312C DE2812C DE2818C SD3118 SD3112 SD12 SD10 LPS3015 MANUFACTURER * Typical DCR Input/Output Capacitor Selection Low ESR (equivalent series resistance) ceramic capacitors should be used at the switching regulator outputs as well as the input supply. Only X5R or X7R ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. A 10μF output capacitor is sufficient for most applications. For good transient response and stability the output capacitor should retain at least 4μF of capacitance over operating temperature and bias voltage. The input supply should be bypassed with a 10μF capacitor, or greater. Consult with capacitor manufacturers for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer 3562fa 16 LTC3562 APPLICATIONS INFORMATION very thin (