EVALUATION KIT AVAILABLE 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 General Description Benefits and Features The MAX1709 sets a new standard of space savings for high-power, step-up DC-DC conversion. It delivers up to 20W at a fixed (3.3V or 5V) or adjustable (2.5V to 5.5V) output, using an on-chip power MOSFET from a +0.7V to +5V supply. Fixed-frequency PWM operation ensures that the switching noise spectrum is constrained to the 600kHz fundamental and its harmonics, allowing easy postfiltering for noise reduction. External clock synchronization capability allows for even tighter noise spectrum control. Quiescent power consumption is less than 1mW to extend operating time in battery-powered systems. Two control inputs (ONA, ONB) allow simple push-on, push-off control through a single momentary pushbutton switch, as well as conventional on/off logic control. The MAX1709 also features programmable soft-start and current limit for design flexibility and optimum performance with batteries. * Integration Reduces External Component Count to Save Space * On-Chip 10A Power MOSFET * 5V, 4A Output from a 3.3V Input * Fixed 3.3V or 5V Output Voltage or Adjustable (2.5V to 5.5V) * Input Voltage Range Down to 0.7V * Constant Frequency Reduces Post-Filtering * Low-Noise, Constant-Frequency Operation (600kHz) * Synchronizable Switching Frequency (350kHz to 1000kHz) The MAX1709 is supplied in both a high-power TSSOP package, which allows a 10ARMS switch current and a 4A output, and a narrow SO package, which supplies a 2.4A output with a switch rated at 6ARMS. Although the narrow SO device has a lower RMS switch rating, it has the same peak switch current rating as the TSSOP device, and so can supply 4A loads intermittently. If loads of 2A or less are required, refer to the MAX1708. Routers, Servers, Workstations, Card Racks Local 2.5V to 3.3V or 5V Conversion Local 3.3V to 5V Conversion 3.6V or 5V RF PAs in Communications Handsets Typical Operating Circuit 1H SYNC OR INTERNAL CLK LX MAX1709 GND SS/LIM REF PART TEMP RANGE -40C to +85C 16 Narrow SO MAX1709EUI+ -40C to +85C 28 TSSOP-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. OUT TOP VIEW ONA 1 28 ONB LX 2 27 CLK LX 3 OUTPUT 3.3V, 5V, OR ADJ UP TO 4A 26 3.3/5 MAX1709 25 NC LX 5 24 NC LX 6 23 PGND LX 7 22 PGND LX 8 21 PGND NC 9 20 PGND NC 10 19 PGND GND 11 18 PGND SS/ILM 12 17 NC REF 13 16 FB GND 14 15 OUT TSSOP-EP 19-1724; Rev 3; 2/15 PIN-PACKAGE MAX1709ESE LX 4 INPUT 1V TO 5V ONA Ordering Information Pin Configuration Applications OFF ON * Lower Power Consumption Extends Battery Life * 1mW Quiescent Power 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Absolute Maximum Ratings ONA, ONB, OUT, SS/LIM, 3.3/5 to GND ...............-0.3V to +6.0V LX to PGND ...........................................................-0.3V to +6.0V FB, CLK, REF to GND.............................. -0.3V to (VOUT + 0.3V) PGND to GND .......................................................-0.3V to +0.3V Continuous Power Dissipation (TA = +70C) 16-Pin Narrow SO (derate 16.5mW/C above +70C) .....1.3W 28-Pin TSSOP Exposed Pad (derate 23.8mW/C above +70C) ...................................1.9W 28-Pin TSSOP Exposed Pad Junction-to-Exposed Pad Thermal Resistance ............................................1.2C/W Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Electrical Characteristics (VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS 3.26 3.34 3.42 5.05 5.17 -0.25 -0.45 1.240 1.265 V 1 200 nA 5.5 V Measured between 1A < ISW < 3A (Note 2) ISW = 1A UNITS 4.92 Load Regulation VFB = +1.5V MAX 3.3/5 = GND, ISW = 1A VFB < 0.1V (Note 1) FB Input Current TYP 3.3/5 = OUT, ISW = 1A Output Voltage FB Regulation Voltage MIN Output Voltage Adjust Range 1.215 2.5 V %/A Output Undervoltage Lockout (Note 3) 2.0 2.3 V Frequency in Startup Mode VOUT =1.5V 40 400 kHz Minimum Startup Voltage IOUT < 1mA (Note 1), TA = +25C (Note 4) 1.1 V Minimum Operating Voltage (Note 5) Soft-Start Pin Current VSS/LIM = 1V 4 5.0 A OUT Supply Current VFB = 1.5V (Note 6) 200 440 A V ONB = 3.6V 0.1 5 A VLX = V ONB = VOUT = +5.5V 0.1 40 A 22 40 m OUT Leakage Current In Shutdown LX Leakage Current n-Channel Switch On-Resistance n-Channel Current Limit RMS Switch Current 0.7 3.2 SS/LIM = open 7.5 SS/LIM = 150k to GND 3.5 V 9 12 5 6.5 MAX1709EUI+ 10 MAX1709ESE 6 Reference Voltage IREF = 0 Reference Load Regulation -1A < IREF < 50A Reference Supply Rejection +2.5V < VOUT < +5.5V 1.245 A ARMS 1.260 1.275 V 4 10 mV 0.2 5 mV ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V 0.2 x VOUT CLK, 2.7V < VOUT < 5.5V 0.2 x VOUT Input Low Level (Note 7) www.maximintegrated.com 0.9 V Maxim Integrated | 2 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Electrical Characteristics (continued) (VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input High Level Logic Input Current CONDITIONS MIN ONA, ONB, 3.3/5, 1.2V < VOUT <5.5 0.8 x VOUT CLK, 2.7 V< VOUT < 5.5V 0.8 x VOUT TYP MAX UNITS V ONA, ONB, CLK, 3.3/5 1 A Internal Oscillator Frequency 520 600 680 kHz Maximum Duty Cycle 82 90 94 % 1000 kHz 50 ns External Clock Frequency Range CLK Pulse Width (Note 8) CLK Rise/Fall Time (Note 8) 350 100 ns Electrical Characteristics (VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = -40C to +85C, unless otherwise noted.) (Note 9) PARAMETER Output Voltage CONDITIONS MIN 3.45 (Note 1) 3.3/5 = OUT, ISW = 1A 4.9 5.2 1.21 1.27 V 200 nA -0.45 %/A 5.2 A 5 A 400 A 40 m ISW = 1A VFB = +1.5V Load Regulation Measured between 1A < ISW < 5A (Note 2) Soft-Start Pin Current SS/LIM = 1V OUT Leakage Current in Shutdown V ONB = 3.6V OUT Supply Current VFB = 1.5V (Note 6) 3.2 n-Channel Switch On-Resistance www.maximintegrated.com UNITS 3.24 FB Input Current Reference Voltage MAX 3.3/5 = GND, ISW = 1A FB Regulation Voltage n-Channel Current Limit TYP VFB < 0.1V, VIN = +2.4V SS/LIM = unconnected 7.5 15 SS/LIM = 150k to GND 3.5 7 IREF = 0 1.24 1.28 V V V Maxim Integrated | 3 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Electrical Characteristics (continued) (VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = -40C to +85C, unless otherwise noted.) (Note 9) PARAMETER CONDITIONS MIN MAX UNITS ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V 0.2 x VOUT V CLK, 2.7V < VOUT < 5.5V 0.2 x VOUT Input Low Level (Note 7) ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V 0.8 x VOUT CLK, VOUT = 5.5V 0.8 x VOUT Input High Level Logic Input Current ONA, ONB, CLK, 3.3/5 TYP V 1 A Internal Oscillator Frequency 500 700 kHz Maximum Duty Cycle 80 95 % External Clock Frequency Range 350 1000 kHz 50 ns CLK/SEL Pulse Width (Note 8) CLK/SEL Rise/Fall Time (Note 8) 100 ns Note 1: Output voltage is specified at 1A switch current ISW, which is equivalent to approximately 1A (VIN / VOUT) of load current. Note 2: Load regulation is measured by forcing specified switch current and straight-line calculation of change in output voltage in external feedback mode. Note that the equivalent load current is approximately ISW (VIN / VOUT). Note 3: Until undervoltage lockout is reached, the device remains in startup mode. Do not apply full load until this voltage is reached. Note 4: Startup is tested with Figure 1's circuit. Output current is measured when both the input and output voltages are applied. Note 5: Minimum operating voltage. The MAX1709 is bootstrapped and will operate down to a 0.7V input once started. Note 6: Supply current is measured from the OUT pin to the output voltage (+3.3V). This correlates directly with actual input supply current but is reduced in value according to the step-up ratio and efficiency. Note 7: ONA and ONB inputs have approximately 0.15V hysteresis. Note 8: Guaranteed by design, not production tested. Note 9: Specifications to -40C are guaranteed by design, not production tested. www.maximintegrated.com Maxim Integrated | 4 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Typical Operating Characteristics (TA = +25C, unless otherwise noted.) 70 60 50 40 70 50 40 30 20 20 10 10 0 VIN = 2.5V 60 30 86.0 85.5 0.01 0.1 1 10 85.0 84.5 84.0 83.5 83.0 0 0.001 0.01 0.1 1 0.4 10 0.5 0.6 0.7 0.8 0.9 OUTPUT CURRENT (A) OUTPUT CURRENT (A) OPERATING FREQUENCY (MHz) LOAD REGULATION (VIN = 3.3V, VOUT = 5V) LINE REGULATION (VOUT = 5V, IOUT = 1A) NO-LOAD INPUT CURRENT vs. INPUT VOLTAGE 0.6 0 0.4 INPUT VOLTAGE INCREASING INPUT CURRENT (mA) VOUT REGULATION (%) 1 1000 0.2 0 -0.2 1.0 MAX1709 TOC06 0.8 MAX1709 TOC04 2 MAX1709 TOC05 0.001 VOUT REGULATION (%) VIN = 3.3V 80 EFFICIENCY (%) VIN = 1.2V 90 EFFICIENCY (%) VIN = 2.5V 80 EFFICIENCY (%) 100 MAX1709 TOC02 90 MAX1709 TOC01 100 EFFICIENCY vs. SWITCHING FREQUENCY (VIN = 3.3V, VOUT = 5V, IOUT = 2A) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V) MAX1709 TOC03 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V) 100 INPUT VOLTAGE DECREASING 10 VOUT = 5V -0.4 -1 1 -0.6 2 3 4 3.5 VOUT = 3.3V 1.4 TA = -40C 1.0 TA = +25C VOUT = 5V 0.01 0.1 www.maximintegrated.com 1 10 2.0 1.5 2.5 3.0 3.5 25 20 -0.5 -1.0 15 10 5 0 VOUT = 3.3V -5 -10 -2.0 LOAD CURRENT (A) 1.0 NOISE vs. FREQUENCY 0 -1.5 TA = +85C 0.5 30 NOISE (mVRMS) 1.8 1.6 0.5 FREQUENCY CHANGE (%) 2.0 0 4.0 INPUT VOLTAGE (V) 1.0 MAX1709 TOC07 2.2 0.001 3.0 SWITCHING FREQUENCY vs. TEMPERATURE 2.4 0.8 2.5 STARTUP VOLTAGE vs. LOAD CURRENT 2.6 0.6 2.0 INPUT VOLTAGE (V) 2.8 STARTUP VOLTAGE (V) 5 OUTPUT CURRENT (A) MAX1709 TOC09 1 MAX1709 TOC08 0 1.2 VOUT = 3.3V 0.1 -0.8 -2 -40 -15 10 35 TEMPERATURE (C) 60 85 0.1 1 10 FREQUENCY (MHz) Maxim Integrated | 5 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) SWITCH CURRENT LIMIT vs. SS/LIM RESISTANCE SWITCH CURRENT LIMIT vs. TEMPERATURE 11.0 5V VLX 5V/div 0 CURRENT LIMIT (A) 8 CURRENT LIMIT (A) MAX1709-13a MAX1709-12 9 HEAVY SWITCHING WAVEFORM 11.5 MAX1709 TOC10 10 7 6 5 10.5 10.0 9.0 4 VOUT 100mV/div 5V 9.5 3 8.5 2 8.0 VOUT = 3.3V 4A IL 2A/div 2A IOUT = 2A 50 100 150 200 250 -40 300 -15 10 35 SS/LIM RESISTANCE (k) TEMPERATURE (C) HEAVY SWITCHING WAVEFORM (WITH LC FILTER) LINE-TRANSIENT RESPONSE 60 85 1s/div LOAD-TRANSIENT RESPONSE MAX1709-14 MAX1709-13b MAX1709-15 3A 5V VLX 5V/div 0 IOUT 2A/div 1A 3.5V VIN 0.5V/div 3V VOUT 100mV/div 5V VOUT 100mV/ 5V 6A 4A IL 2A/div 2A VOUT 50mV/d 5V IL 2A/div 4A 2A IOUT = 1A 100s/div 1s/div 20s/div IOUT = 2A L = 12.5nH (COILCRAFT A04T) C = 1F SHUTDOWN WITH SOFT-START (CSS = 0.1F) SHUTDOWN WITH SOFT-START (CSS = 0.01F) MAX1709-16 5V VONA 5V/div 0 SHUTDOWN WITHOUT SOFT-START MAX1709-18 MAX1709-17 5V VONA 5V/div 0 2A 4A IIN 2A/div 2A VOUT 2V/div 4V 0 IIN 2A/div 2V VOUT 2V/div www.maximintegrated.com IIN 2A/div 2A VOUT 2V/div 4V 2V 2V 1ms/div CSS = 0.1F ROUT = 5 VONB = VOUT 4A 0 0 4V VONA 5V/div 0 6A 6A 4A 5V 1ms/div 1ms/div CSS = 0.01F ROUT = 5 VONB = VOUT CSS = 0 ROUT = 5 VONB = VOUT Maxim Integrated | 6 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Pin Description PIN TSSOP NARROW SO NAME 1 1 ONA 2-8 2, 3, 4 LX 11, 14 5, 8 GND FUNCTION On-Control Input. When ONA = high OR ONB = low, the device turns on Drain of n-Channel Power Switch. Connect pins 2, 3, and 4 together. Connect external Schottky diode from LX to OUT. Ground. Connect ground inputs together, then connect to PGND. Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to GND to control the rate at which the device reaches current limit (soft-start). To reduce the current limit from the preset values, connect a resistor from SS/LIM to GND (see Design Procedure). During shutdown, this pin is internally pulled to GND to discharge the soft-start capacitor. 12 6 SS/LIM 13 7 REF 1.26V Voltage Reference Output. Bypass with a 0.22F capacitor to GND. Maximum REF load is 50A. 15 9 OUT Output Voltage Sense Input. The device is powered from OUT. Bypass with a 0.1F to PGND with less than 5mm trace length. Connect a 2 series resistor from the output filter capacitor to OUT (Figure 1). DC-DC Converter Feedback Input. Connect FB to GND for internally set output voltage (see 3.3/5 pin description). Connect a resistor-divider from the output to set the output voltage in the +2.5V to +5.5V range. FB regulates to +1.25V (Figure 4). 16 10 FB 18-23 11, 12, 13 PGND Power Ground. Source of n-channel power MOSFET switch. Connect PGND inputs together, then connect to GND. 26 14 3.3/5 Output Voltage Selection Pin. When FB is connected to GND, the regulator uses internal feedback to set the output voltage. 3.3/5 = low sets output to 3.3V; 3.3/5 = high sets output to 5V. If an external divider is used at FB, connect 3.3/5 to ground. 27 15 CLK Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator. Optionally, drive with an external clock for external synchronization. 28 16 ONB Shutdown Input. When ONB = high AND ONA = low, the device turns off (Table 1). 9, 10, 17, 24, 25 -- N.C. No Connect. Not internally connected. EP -- EP www.maximintegrated.com Exposed Pad. Connect to large ground plane for maximum thermal dissipation. Maxim Integrated | 7 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 KEEP TRACES SHORT AND WIDE 1H L1 VIN 1V TO 5V D1 ON-OFF CONTROL C1, C2 2 x 150F ONA ONB LX CLK LX 3.3/5 VOUT 5V C6, C7 2x 150F PGND LX GND MAX1709 R1 C3 GND PGND SS/LIM PGND REF FB GND OUT C4 0.22F R2 2 C5 0.1F Figure 1. Standard Operating Circuit Detailed Description The MAX1709 step-up converter offers high efficiency and high integration for high-power applications. It operates with an input voltage as low as 0.7V and is suitable for single- to 3-cell battery inputs as well as 2.5V or 3.3V regulated supply inputs. The output voltage is preset to +3.3V or +5.0V or can be adjusted with external resistors for voltages between +2.5V to +5.5V. The n-channel switch of the MAX1709EUI+ is rated for 10ARMS and can deliver loads up to 4A, depending on input and output voltage. The n-channel switch of the MAX1709ESE has a 6ARMS rating and supplies up to 2.4A output. The MAX1709ESE has a lower RMS switch rating than the MAX1709EUI+, but has the same peak switch current limit and so can supply 4A loads intermittently. For flexibility, the current limit and soft-start rate are independently programmable. A 600kHz switching frequency allows for a small inductor to be used. The switching frequency is also synchronizable to an external clock ranging from 350kHz to 1000kHz. www.maximintegrated.com ONA, ONB The logic levels at ONA and ONB turn the MAX1709 on or off. When ONA = 1 or ONB = 0, the part is on. When ONA = 0 and ONB = 1, the part is off (Table 1). Logichigh on control can be implemented by tying ONB high and using ONA for shutdown. Implement inverted single-line on/off control by grounding ONA and toggling ONB. Implement momentary pushbutton On/Off as described in the Applications Information section. Both inputs have approximately 0.15V of hysteresis. Switching Frequency The MAX1709 switches at the fixed-frequency internal oscillator rate (600kHz) or can be synchronized to an external clock. Connect CLK to OUT for internal clock operation. Apply a clock signal to CLK to synchronize to an external clock. The frequency can be changed on the fly. The MAX1709 will synchronize to a new external clock rate in two cycles and will take approximately 40s to revert to its internal clock frequency once the external clock pulses stop and CLK is driven high. Table 2 summarizes oscillator operation. Maxim Integrated | 8 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Table 1. On/Off Logic Control Table 2. Selecting Switching Frequency ONA 0 ONB 0 MAX1709 On 0 1 Off 1 0 On 1 1 On CLK 0 1 External clock (350kHz-1000kHz) MODE Not allowed PWM Synchronized PWM UNDERVOLTAGE LOCKOUT OUT MAX1709 IC POWER PWM CONTROLLER 2.15V EN STARTUP Q OSCILLATOR D SEE FIGURE 3. ONA ONB REF 1.260V EN ON RDY REFERENCE EN CLK FB 3.3/5 GND DUAL MODE FB 600kHz OSCILLATOR LX OSC N FB PGND OUT Figure 2. Simplified Functional Diagram Operation The MAX1709 switches at a constant frequency (600kHz) and modulates the MOSFET switch pulse width to control the power transferred per cycle and regulate the voltage across the load. In low-noise applications, the fundamental and the harmonics generated by the fixed switching frequency are easily filtered out. Figure 2 shows the simplified functional diagram for the MAX1709. Figure 3 shows the simplified PWM controller functional diagram. The MAX1709 enters synchronized current-mode PWM when a clock signal (350kHz < f CLK < 1000kHz) is applied to CLK. For wireless or noise-sensitive applications, this ensures that switching harmonics are predictable and kept outside the IF frequency band(s). High-frequency operation permits low-magnitude output ripple voltage and minimum inductor and filter capacitor size. Switching losses will increase at the higher frequencies (see Power Dissipation). Setting the Output Voltage The MAX1709 features Dual-ModeTM operation. When FB is connected to ground, the MAX1709 generates a fixed output voltage of either +3.3V or +5V, depending on the logic applied to the 3.3/5 input (Figure 1). The output can be configured for other voltages, using two external resistors as shown in Figure 4. To set the output voltage externally, choose an R3 value that is large enough to minimize load at the output but small enough to minimize errors due to leakage and the time constant to FB. A value of R3 50k is required. V R4 = R3 OUT - 1 VFB where VFB = 1.24V. Soft-Start/Current-Limit Adjustment (SS/LIM) The soft-start pin allows the soft-start time to be adjusted by connecting a capacitor from SS/LIM to ground. Select capacitor C3 (connected to SS/LIM pin) as: C3 (in F) = 3.2 tSS where tSS is the time (in seconds) it takes the switch current limit to reach full value. To improve efficiency or reduce inductor size at reduced load currents, the current limit can be reduced Dual Mode is a trademark of Maxim Integrated Products, Inc. www.maximintegrated.com Maxim Integrated | 9 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Table 3. Component Selection Guide PRODUCTION INDUCTORS Surface mount CAPACITORS Coilcraft DO3316P-102HC Panasonic EEFUE0J151R Motorola MBRD1035CTL Coiltronics UP2B-1R0 Sanyo 6TPC100M STM-Microelectronics STPS8L30B at a different frequency, scale the inductor value with the inverse of frequency (L1 = 1H 600kHz / fSYNC). The PWM design tolerates inductor values within 25% of this calculated value, so choose the closest standard inductor value. For example, use 1.5H for 350kHz and 0.68H for 1MHz. Table 4. Component Suppliers SUPPLIER PHONE FAX Coilcraft 847-639-6400 847-639-1489 Coiltronics 561-241-7876 561-241-9339 Motorola 602-303-5454 602-994-6430 Panasonic 714-373-7939 714-373-7183 STMMicroelectronics 617-259-0300 617-259-9442 from its nominal value (see Electrical Characteristics). A resistor (R1 in Figure 1) between SS/LIM and ground reduces the current limit as follows: R1 = 312.5k x DIODES I1 (R1 312.5k) ILIM where I1 is the desired current limit in amperes, and I LIM is the current limit value from the Electrical Characteristics. Inductors with a ferrite core or equivalent are recommended; powder iron cores are not recommended for use at high switching frequencies. Ensure the inductor's saturation rating (the current at which the core begins to saturate and inductance falls) exceeds the internal current limit. Note that this current may be reduced through SS/LIM if less than the MAX1709's full load current is needed (see Electrical Characteristics for ratings). For highest efficiency, use a coil with low DC resistance, preferably under 10m. To minimize radiated noise, use a toroid, pot core, or shielded inductor. See Tables 3 and 4 for a list of recommended components and component suppliers. To calculate the maximum output current (in amperes), use the following equation: V + VD - VIN IOUT(MAX) = D' ILIM - D' OUT 2 x x L1 Design Procedure Inductor Selection (L1) The MAX1709's high switching frequency allows the use of a small-size inductor. Use a 1.0H inductor for 600kHz operation. If the MAX1709 will be synchronized where: VIN = input voltage VIN FB REF SLOPE COMP LX R Q N VOUT LX S MAX1709 R4 SS/LIM 12.5 (LIMITED TO 100mV) OSCILLATOR Figure 3. Simplified PWM Controller Functional Diagram www.maximintegrated.com FB 11m PGND KEEP SHORT R3 Figure 4. Adjustable Output Voltage Maxim Integrated | 10 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Output Filter Capacitors (C6, C7) 270k ON/OFF C MAX1709 ONB VDD I/O ONA I/O 270k 0.1F Figure 5. Momentary Pushbutton On-Off Switch VD = forward voltage drop of the Schottky diode at ILIM current VOUT = output voltage D' = (VIN) / (VOUT + VD), assuming switch voltage drop is negligible f = switching frequency L1 = inductor value ILIM = minimum value of switch current limit from Electrical Characteristics or set by RSET/LIM. Diode Selection (D1) The MAX1709's high switching frequency demands a high-speed rectifier. Schottky diodes, such as the MBRD1035CTL or STPS8L30B (Table 3), are recommended. The diode's current rating must exceed the maximum load current, and its breakdown voltage must exceed VOUT. The diode must be placed within 10mm of the LX switching node and the output filter capacitor. The diode also must be able to dissipate the power calculated by the following equation: PDIODE = IOUT VD where IOUT is the average load current and VD is the diode forward voltage at the peak switch current. Capacitor Selection Input Bypass Capacitors (C1, C2) Two 150F, low-ESR tantalum input capacitors will reduce peak currents and reflected noise due to inductor current ripple. Lower ESR allows for lower input ripple current, but combined ESR values up to 50m are acceptable. Smaller ceramic capacitors may also be used for light loads or in applications that can tolerate higher input current ripple. www.maximintegrated.com The output filter capacitor ESR must be kept under 15m for stable operation. Two parallel 150F polymer capacitors (Panasonic EEFUE0J151R) typically exhibit 5m of ESR. This translates to approximately 35mV of output ripple at 7A switch current. Bypass the MAX1709 IC supply input (OUT) with a 0.1F ceramic capacitor to GND and connect a 2 series resistor to OUT (R2, as shown in Figure 1). Power Dissipation The MAX1709 output current may be more limited by package power dissipation than by the current rating of the on-chip switch. For pulsed loads, output currents of 4 Amps or more can be supplied with either the MAX1709EUI+ or MAX1709ESE, but the RMS (or thermal) limit of the MAX1709ESE is lower (6ARMS) than that of the MAX1709EUI+ (10ARMS). Continuous output current depends on the input and output voltage, operating temperature, and external components. The major components of the MAX1709 dissipated power (PD, i.e., power dissipated as heat in the IC and NOT delivered to the load) are: 1) Internal switch conduction losses - PSW 2) Internal switch transition losses - PTRAN 3) Internal capacitive losses - PCAP These are losses that directly dissipate heat in the MAX1709, but keep in mind that other losses, such as those in the external diode and inductor, increase input power by reducing overall efficiency, and so indirectly contribute to MAX1709 heating. Approximate equations for the loss terms are as follows. Values in {} are example values for a 3.3V input, 4V output, 4A design. A conservative efficiency estimate for the MAX1709 boosting from 3.3V to 5V at 4A is 81%. Total estimated power loss is then: {4.7W} PLOSS = (POUT / 0.81) - POUT The total loss consists of: Diode Loss = D' x ISW x VD {2.5W} Inductor Loss (resistive loss + dynamic loss estimate) {0.58W} External Capacitive Loss = (1 - D') x ISW2 x RCAP-ESR (ESR est. = 10m) {0.27W} MAX1709 Internal Loss, PD(MAX1709) {1.35W} Maxim Integrated | 11 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Approximate equations for the MAX1709 internal loss terms are as follows. Values in {} are example values for a 3.3V input, 4V output, 4A design: PD(MAX1709) = PSW + PTRAN + PCAP {1.35W} where: PSW = (1 - D') x ISW2 x RSW {1.08W} PTRAN = (VOUT + VD) x ISW x tSW x f / 3 {0.18W} PCAP = (CDIO + CDSW + CGSW) x (VOUT + VD)2 f {0.09W} where: D' = duty factor of the n-channel switch = VIN / (VOUT + VD) (Note: D' = 1 means the switch is always off) {0.6} ISW, the approximate peak switch current = IOUT / (D' x eff), {8.23A} (with eff. estimated at 81%) RSW = Internal n-channel switch resistance (estimate for elevated die temperature) VD = forward voltage of the external rectifier tSW = the transition time of the n-channel switch f = the switching rate of the MAX1709 CDIO = rectifier capacitance {0.04W) {0.5V} {20ns} {600kHz} The MAX1709ESE and MAX1709EUI+ both utilize PC board area for heatsinking. Package dissipation ratings in the Absolute Maximum Ratings section assume 1in2 of 1oz copper. The MAX1709EUI+ has superior power-dissipating ability due to an exposed metal pad on the underside of the package. The thermal resistance from the die to the exposed pad is a very low 1.2C/W. The MAX1709ESE's ability to dissipate power will especially depend on the PC board design. Typical thermal resistance for 1in2 of copper is 34C/W. For tighter layouts, 0.5in2 typically exhibits 40C/W. Adding multiple vias under the MAX1709EUI+ to conduct heat to the bottom of the board will also help dissipate power. Due to high inductor current levels and fast switching waveforms, proper PC board layout is essential. Protect sensitive analog grounds by using a star ground configuration. Connect PGND, the input bypass capacitor ground lead, and the output filter capacitor ground lead to a single point (star ground configuration). In addition, minimize trace lengths to reduce stray capacitance and trace resistance, especially from the LX pins to the catch diode (D1) and output capacitors (C6 and C7) to PGND pins. If an external resistor-divider is used to set the output voltage (Figure 4), the trace from FB to the resistors must be extremely short and must be shielded from switching signals, such as CLK or LX. Refer to a layout example in the MAX1709EVKIT data sheet. {1nF} CDSW = internal n-channel drain capacitance {2.5nF} CGSW = internal n-channel gate capacitance {1.5nF} Applications Information Using a Momentary On/Off Switch A momentary pushbutton switch can be used to turn the MAX1709 on and off. As shown in Figure 5, when ONA is pulled low and ONB is pulled high, the part is off. When the momentary switch is pressed, ONB is pulled low and the regulator turns on. The switch should be on long enough for the microcontroller to exit reset. The controller issues a logic high to ONA, which guarantees that the part will stay on regardless of the subsequent switch state. To turn the regulator off, press the switch long enough for the controller to read the switch status and pull ONA low. When the switch is released, ONB pulls high and the regulator turns off. www.maximintegrated.com Layout Considerations Chip Information TRANSISTOR COUNT: 1112 Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 16 SOIC (N) S16+8 21-0041 90-0097 28 TSSOP-EP U28E+4 21-0108 90-0146 Maxim Integrated | 12 4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709 Revision History REVISION NUMBER REVISION DATE 3 2/15 DESCRIPTION Updated the Benefits and Features section PAGES CHANGED 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated's website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. (c) 2015 Maxim Integrated Products, Inc. | 13 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX1709ESE+ MAX1709ESE+T MAX1709EUI+ MAX1709EUI+T MAX1709EUI/GG8-T