4A, Low-Noise, High-Frequency, Step-Up DC-DC Converter MAX1709

Transcription

1 EALUATION KIT AAILABLE MAX179 General Description The MAX179 sets a new standard of space savings for high-power, step-up DC-DC conversion. It delivers up to 2W at a fixed (3.3 or ) or adjustable (2. to 5.) output, using an on-chip power MOSFET from a +.7 to + supply. Fixed-frequency PWM operation ensures that the switching noise spectrum is constrained to the 6kHz 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 MAX179 also features programmable soft-start and current limit for design flexibility and optimum performance with batteries. The MAX179 is supplied in both a high-power TSSOP package, which allows a 1A RMS switch current and a 4A output, and a narrow SO package, which supplies a 2.4A output with a switch rated at 6A RMS. 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 MAX178. Applications Routers, Servers, Workstations, Card Racks Local 2. to 3.3 or Conversion Local 3.3 to Conversion 3.6 or RF PAs in Communications Handsets Typical Operating Circuit INPUT 1 TO Benefits and Features Integration Reduces External Component Count to Save Space On-Chip 1A Power MOSFET, 4A Output from a 3.3 Input Fixed 3.3 or Output oltage or Adjustable (2. to 5.) Input oltage Range Down to.7 Constant Frequency Reduces Post-Filtering Low-Noise, Constant-Frequency Operation (6kHz) Synchronizable Switching Frequency (35kHz to 1kHz) Lower Power Consumption Extends Battery Life 1mW Quiescent Power Ordering Information PART TEMP RANGE PIN-PACKAGE MAX179ESE -4 C to +85 C 16 Narrow SO MAX179EUI+ -4 C to +85 C 28 TSSOP-EP* +Denotes a lead(pb)-free/rohs-compliant package. *EP = Exposed pad. Pin Configuration TOP IEW ONA MAX ONB 27 CLK /5 25 NC 24 NC 23 P 1µH 7 22 P OFF ON SYNC OR INTERNAL ONA MAX179 CLK SS/LIM OUTPUT 3.3,, OR ADJ UP TO 4A NC NC SS/ILM 8 21 P 9 2 P 1 19 P P NC REF OUT REF FB OUT TSSOP-EP ; Rev 3; 2/15

2 MAX179 Absolute Maximum Ratings ONA, ONB, OUT, SS/LIM, 3.3/5 to to +6. to P to +6. FB, CLK, REF to to ( +.3) P to to +.3 Continuous Power Dissipation (T A = +7 C) 16-Pin Narrow SO (derate 16.5mW/ C above +7 C)...1.3W 28-Pin TSSOP Exposed Pad (derate 23.8mW/ C above +7 C)...1.9W 28-Pin TSSOP Exposed Pad Junction-to-Exposed Pad Thermal Resistance C/W Operating Temperature Range...-4 C to +85 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s)...+3 C 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 ( = CLK = +3.6, ONA = ONB = FB =, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER CONDITIONS MIN TYP MAX UNITS Output oltage FB <.1 (Note 1) 3.3/5 =, I SW = 1A /5 = OUT, I SW = 1A Load Regulation Measured between 1A < I SW < 3A (Note 2) %/A FB Regulation oltage I SW = 1A FB Input Current FB = na Output oltage Adjust Range Output Undervoltage Lockout (Note 3) Frequency in Startup Mode = khz Minimum Startup oltage I OUT < 1mA (Note 1), T A = +25 C (Note 4) Minimum Operating oltage (Note 5).7 Soft-Start Pin Current SS/LIM = µa OUT Supply Current FB = 1. (Note 6) 2 44 µa OUT Leakage Current In Shutdown ONB = µa Leakage Current = ONB = = µa n-channel Switch On-Resistance n-channel Current Limit RMS Switch Current 22 4 mω SS/LIM = open SS/LIM = 15kΩ to MAX179EUI+ 1 MAX179ESE 6 Reference oltage I REF = Reference Load Regulation -1µA < I REF < 5µA 4 1 m Reference Supply Rejection +2. < < m Input Low Level (Note 7) ONA, ONB, 3.3/5, 1.2 < < 5. CLK, 2.7 < < A A RMS Maxim Integrated 2

3 MAX179 Electrical Characteristics (continued) ( = CLK = +3.6, ONA = ONB = FB =, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) Input High Level PARAMETER CONDITIONS MIN TYP MAX UNITS ONA, ONB, 3.3/5, 1.2 < <5.5.8 CLK, 2.7 < < 5..8 Logic Input Current ONA, ONB, CLK, 3.3/5 1 µa Internal Oscillator Frequency khz Maximum Duty Cycle % External Clock Frequency Range 35 1 khz CLK Pulse Width (Note 8) 1 ns CLK Rise/Fall Time (Note 8) 5 ns Electrical Characteristics ( = CLK = +3.6, ONA = ONB = FB =, T A = -4 C to +85 C, unless otherwise noted.) (Note 9) Output oltage PARAMETER CONDITIONS MIN TYP MAX UNITS FB <.1, IN = /5 =, I SW = 1A (Note 1) 3.3/5 = OUT, I SW = 1A FB Regulation oltage I SW = 1A FB Input Current FB = na Load Regulation Measured between 1A < I SW < 5A (Note 2) -.45 %/A Soft-Start Pin Current SS/LIM = µa OUT Leakage Current in Shutdown ONB = µa OUT Supply Current FB = 1. (Note 6) 4 µa n-channel Switch On-Resistance n-channel Current Limit SS/LIM = unconnected SS/LIM = 15kΩ to mω Reference oltage I REF = Maxim Integrated 3

4 MAX179 Electrical Characteristics (continued) ( = CLK = +3.6, ONA = ONB = FB =, T A = -4 C to +85 C, unless otherwise noted.) (Note 9) PARAMETER CONDITIONS MIN TYP MAX UNITS Input Low Level (Note 7) Input High Level ONA, ONB, 3.3/5, 1.2 < < 5. CLK, 2.7 < < 5. ONA, ONB, 3.3/5, 1.2 < < 5. CLK, = 5. Logic Input Current ONA, ONB, CLK, 3.3/5 1 µa Internal Oscillator Frequency 5 7 khz Maximum Duty Cycle 8 95 % External Clock Frequency Range Note 1: Output voltage is specified at 1A switch current I SW, which is equivalent to approximately 1A ( IN / ) 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 I SW ( IN / ). 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 MAX179 is bootstrapped and will operate down to a.7 input once started. Note 6: Supply current is measured from the OUT pin to the output voltage (+3.3). 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.1 hysteresis. Note 8: Guaranteed by design, not production tested. Note 9: Specifications to -4 C are guaranteed by design, not production tested khz CLK/SEL Pulse Width (Note 8) 1 ns CLK/SEL Rise/Fall Time (Note 8) 5 ns Maxim Integrated 4

5 MAX179 Typical Operating Characteristics (T A = +25 C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT ( = 3.3) IN = 2. MAX179 TOC EFFICIENCY vs. OUTPUT CURRENT ( = ) IN = 3.3 MAX179 TOC EFFICIENCY vs. SWITCHING FREQUENCY ( IN = 3.3, =, I OUT = 2A) MAX179 TOC3 EFFICIENCY (%) IN = 1.2 EFFICIENCY (%) IN = 2. EFFICIENCY (%) OUTPUT CURRENT (A) OUTPUT CURRENT (A) OPERATING FREQUENCY (MHz) OUT REGULATION (%) LOAD REGULATION ( IN = 3.3, = ) MAX179 TOC4 OUT REGULATION (%) LINE REGULATION ( =, I OUT = 1A) MAX179 TOC5 INPUT CURRENT (ma) NO-LOAD INPUT CURRENT vs. INPUT OLTAGE INPUT OLTAGE INCREASING = 3.3 INPUT OLTAGE DECREASING = MAX179 TOC OUTPUT CURRENT (A) INPUT OLTAGE () INPUT OLTAGE () STARTUP OLTAGE () T A = -4 C T A = +25 C T A = +85 C STARTUP OLTAGE vs. LOAD CURRENT = LOAD CURRENT (A) = MAX179 TOC7 FREQUENCY CHANGE (%) SWITCHING FREQUENCY vs. TEMPERATURE TEMPERATURE ( C) = 3.3 MAX179 TOC8 NOISE (mrms) NOISE vs. FREQUENCY FREQUENCY (MHz) MAX179 TOC9 Maxim Integrated 5

6 MAX179 Typical Operating Characteristics (continued) (T A = +25 C, unless otherwise noted.) CURRENT LIMIT (A) SWITCH CURRENT LIMIT vs. SS/LIM RESISTANCE SS/LIM RESISTANCE (kω) MAX179 TOC1 CURRENT LIMIT (A) SWITCH CURRENT LIMIT vs. TEMPERATURE = TEMPERATURE ( C) MAX A 2A HEAY SWITCHING WAEFORM MAX179-13a I OUT = 2A 1μs/div /div 1m/div I L HEAY SWITCHING WAEFORM (WITH LC FILTER) MAX179-13b LINE-TRANSIENT RESPONSE MAX LOAD-TRANSIENT RESPONSE MAX /div 3. 3 IN./div 3A 1A I OUT 1m/div 1m/ 6A 4A 2A I L I OUT = 1A 5m/d 4A 2A I L 1μs/div I OUT = 2A L = 12.5nH (COILCRAFT A4T) C = 1μF SHUTDOWN WITH SOFT-START (C SS =.1μF) MAX μs/div SHUTDOWN WITH SOFT-START (C SS =.1μF) MAX μs/div SHUTDOWN WITHOUT SOFT-START MAX ONA /div ONA /div ONA /div 6A 6A 4A 2A I IN 4A 2A I IN 4A 2A I IN 4 2/div 4 2/div 4 2/div 2 C SS =.1μF R OUT = 5Ω ONB = 1ms/div 2 C SS =.1μF R OUT = 5Ω ONB = 1ms/div 2 C SS = R OUT = 5Ω ONB = 1ms/div Maxim Integrated 6

7 MAX179 Pin Description PIN TSSOP NARROW SO NAME FUNCTION 1 1 ONA On-Control Input. When ONA = high OR ONB = low, the device turns on 2 8 2, 3, 4 Drain of n-channel Power Switch. Connect pins 2, 3, and 4 together. Connect external Schottky diode from to OUT. 11, 14 5, 8 Ground. Connect ground inputs together, then connect to P SS/LIM 13 7 REF 15 9 OUT 16 1 FB , 12, 13 P Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to 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 (see Design Procedure). During shutdown, this pin is internally pulled to to discharge the soft-start capacitor oltage Reference Output. Bypass with a.22µf capacitor to. Maximum REF load is 5µA. Output oltage Sense Input. The device is powered from OUT. Bypass with a.1µf to P with less than 5mm trace length. Connect a 2Ω series resistor from the output filter capacitor to OUT (Figure 1). DC-DC Converter Feedback Input. Connect FB to 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. to +5. range. FB regulates to +1.2 (Figure 4). Power Ground. Source of n-channel power MOSFET switch. Connect P inputs together, then connect to / CLK Output oltage Selection Pin. When FB is connected to, the regulator uses internal feedback to set the output voltage. 3.3/5 = low sets output to 3.3; 3.3/5 = high sets output to. If an external divider is used at FB, connect 3.3/5 to ground. Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator. Optionally, drive with an external clock for external synchronization ONB 9, 1, 17, 24, 25 Shutdown Input. When ONB = high AND ONA = low, the device turns off (Table 1). N.C. No Connect. Not internally connected. EP EP Exposed Pad. Connect to large ground plane for maximum thermal dissipation. Maxim Integrated 7

8 MAX179 KEEP TRACES SHORT AND WIDE 1μH D1 L1 C1, C2 2 x 15μF IN 1 TO ON-OFF CONTROL ONA ONB CLK 3.3/5 C6, C7 2 x 15μF MAX179 P P SS/LIM P R1 C3 C4.22μF REF FB OUT R2 2Ω C5.1μF Figure 1. Standard Operating Circuit Detailed Description The MAX179 step-up converter offers high efficiency and high integration for high-power applications. It operates with an input voltage as low as.7 and is suitable for single- to 3-cell battery inputs as well as 2. or 3.3 regulated supply inputs. The output voltage is preset to +3.3 or +5. or can be adjusted with external resistors for voltages between +2. to +5.. The n-channel switch of the MAX179EUI+ is rated for 1ARMS and can deliver loads up to 4A, depending on input and output voltage. The n-channel switch of the MAX179ESE has a 6ARMS rating and supplies up to 2.4A output. The MAX179ESE has a lower RMS switch rating than the MAX179EUI+, 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 6kHz switching frequency allows for a small inductor to be used. The switching frequency is also synchronizable to an external clock ranging from 35kHz to 1kHz. ONA, ONB The logic levels at ONA and ONB turn the MAX179 on or off. When ONA = 1 or ONB =, the part is on. When ONA = 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.1 of hysteresis. Switching Frequency The MAX179 switches at the fixed-frequency internal oscillator rate (6kHz) 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 MAX179 will synchronize to a new external clock rate in two cycles and will take approximately 4µs 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

9 MAX179 Table 1. On/Off Logic Control ONA ONB MAX179 On 1 Off 1 On 1 1 On Table 2. Selecting Switching Frequency CLK MODE Not allowed 1 PWM External clock Synchronized PWM (35kHz 1kHz) OUT ONA ONB REF CLK FB 3.3/5 IC POWER UNDEROLTAGE LOCKOUT ON RDY REFERENCE DUAL MODE FB OUT MAX179 STARTUP EN Q OSCILLATOR EN 6kHz OSCILLATOR D EN PWM CONTROLLER OSC FB SEE FIGURE 3. N P Figure 2. Simplified Functional Diagram Operation The MAX179 switches at a constant frequency (6kHz) 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 MAX179. Figure 3 shows the simplified PWM controller functional diagram. The MAX179 enters synchronized current-mode PWM when a clock signal (35kHz < f CLK < 1kHz) 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 oltage The MAX179 features Dual-Mode operation. When FB is connected to ground, the MAX179 generates a fixed output voltage of either +3.3 or +, depending Dual Mode is a trademark of Maxim Integrated Products, Inc. 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 5kΩ is required. where FB = R R 4= 3 OUT 1 FB 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 µf) = 3.2 t SS where t SS 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 Maxim Integrated 9

10 MAX179 Table 3. Component Selection Guide PRODUCTION INDUCTORS CAPACITORS DIODES Surface mount Coilcraft DO3316P-12HC Panasonic EEFUEJ151R Motorola MBRD135CTL Coiltronics UP2B-1R Sanyo 6TPC1M STM-Microelectronics STPS8L3B Table 4. Component Suppliers SUPPLIER PHONE FAX Coilcraft Coiltronics Motorola Panasonic STM- Microelectronics from its nominal value (see Electrical Characteristics). A resistor (R1 in Figure 1) between SS/LIM and ground reduces the current limit as follows: I R1 = kΩ 1 R kΩ ILIM where I 1 is the desired current limit in amperes, and I LIM is the current limit value from the Electrical Characteristics. Design Procedure ( ) Inductor Selection (L1) The MAX179 s high switching frequency allows the use of a small-size inductor. Use a 1.µH inductor for 6kHz operation. If the MAX179 will be synchronized at a different frequency, scale the inductor value with the inverse of frequency (L 1 = 1µH 6kHz / f SYNC ). The PWM design tolerates inductor values within ±25% of this calculated value, so choose the closest standard inductor value. For example, use 1.5µH for 35kHz and.68µh for 1MHz. 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 MAX179 s full load current is needed (see Electrical Characteristics for ratings). For highest efficiency, use a coil with low DC resistance, preferably under 1mΩ. 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: I D I D D IN OUT( MAX) = ' LIM ' + 2 ƒ L1 where: IN = input voltage IN FB REF SLOPE COMP R Q N S MAX179 SS/LIM 12.5 (LIMITED TO 1m) OSCILLATOR 11mΩ P FB KEEP SHORT R3 R4 Figure 3. Simplified PWM Controller Functional Diagram Figure 4. Adjustable Output oltage Maxim Integrated 1

11 MAX179 ON/OFF 27k ONB ONA MAX179 μc DD I/O I/O Output Filter Capacitors (C6, C7) The output filter capacitor ESR must be kept under 15mΩ for stable operation. Two parallel 15µF polymer capacitors (Panasonic EEFUEJ151R) typically exhibit 5mΩ of ESR. This translates to approximately 35m of output ripple at 7A switch current. Bypass the MAX179 IC supply input (OUT) with a.1µf ceramic capacitor to and connect a 2Ω series resistor to OUT (R2, as shown in Figure 1)..1μF D = forward voltage drop of the Schottky diode at I LIM current = output voltage D' = ( IN ) / ( + D ), assuming switch voltage drop is negligible f = switching frequency L1 = inductor value I LIM = minimum value of switch current limit from Electrical Characteristics or set by R SET/LIM. Diode Selection (D1) The MAX179 s high switching frequency demands a high-speed rectifier. Schottky diodes, such as the MBRD135CTL or STPS8L3B (Table 3), are recommended. The diode s current rating must exceed the maximum load current, and its breakdown voltage must exceed. The diode must be placed within 1mm of the switching node and the output filter capacitor. The diode also must be able to dissipate the power calculated by the following equation: P DIODE = I OUT D where I OUT is the average load current and D is the diode forward voltage at the peak switch current. Capacitor Selection Input Bypass Capacitors (C1, C2) Two 15µF, 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 5mΩ are acceptable. Smaller ceramic capacitors may also be used for light loads or in applications that can tolerate higher input current ripple. 27k Figure 5. Momentary Pushbutton On-Off Switch Power Dissipation The MAX179 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 MAX179EUI+ or MAX179ESE, but the RMS (or thermal) limit of the MAX179ESE is lower (6ARMS) than that of the MAX179EUI+ (1ARMS). Continuous output current depends on the input and output voltage, operating temperature, and external components. The major components of the MAX179 dissipated power (P D, i.e., power dissipated as heat in the IC and NOT delivered to the load) are: 1) Internal switch conduction losses - P SW 2) Internal switch transition losses - PTRAN 3) Internal capacitive losses - P CAP These are losses that directly dissipate heat in the MAX179, 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 MAX179 heating. Approximate equations for the loss terms are as follows. alues in {} are example values for a 3.3 input, 4 output, 4A design. A conservative efficiency estimate for the MAX179 boosting from 3.3 to at 4A is 81%. Total estimated power loss is then: PLOSS = (P OUT /.81) - P OUT {4.7W} The total loss consists of: Diode Loss = D x ISW x D {2.5W} Inductor Loss (resistive loss + dynamic loss estimate) {.58W} External Capacitive Loss = (1 - D ) x I SW 2 x RCAP-ESR (ESR est. = 1mΩ) {.27W} MAX179 Internal Loss, PD(MAX179) {1.35W} Maxim Integrated 11

12 MAX179 Approximate equations for the MAX179 internal loss terms are as follows. alues in {} are example values for a 3.3 input, 4 output, 4A design: PD(MAX179) = PSW + PTRAN + PCAP {1.35W} where: PSW = (1 - D ) x ISW 2 x RSW {1.8W} P TRAN = (OUT + D) x ISW x t SW x f / 3 {.18W} PCAP = (CDIO + CDSW + CGSW) x ( + D ) 2 f {.9W} where: D = duty factor of the n-channel switch = IN / ( + D ) {.6} (Note: D = 1 means the switch is always off) I SW, the approximate peak switch current = I OUT / (D x eff), {8.23A} (with eff. estimated at 81%) R SW = Internal n-channel switch resistance {.4W) (estimate for elevated die temperature) D = forward voltage of the external rectifier {.} t SW = the transition time of the n-channel switch {2ns} f = the switching rate of the MAX179 {6kHz} C DIO = rectifier capacitance {1nF} C DSW = 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 MAX179 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. Layout Considerations The MAX179ESE and MAX179EUI+ both utilize PC board area for heatsinking. Package dissipation ratings in the Absolute Maximum Ratings section assume 1in 2 of 1oz copper. The MAX179EUI+ 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 1.2 C/W. The MAX179ESE s ability to dissipate power will especially depend on the PC board design. Typical thermal resistance for 1in 2 of copper is 34 C/W. For tighter layouts,.5in 2 typically exhibits 4 C/W. Adding multiple vias under the MAX179EUI+ 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 P, 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 pins to the catch diode (D1) and output capacitors (C6 and C7) to P 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. Refer to a layout example in the MAX179EKIT data sheet. Chip Information TRANSISTOR COUNT: 1112 Package Information For the latest package outline information and land patterns (footprints), go to /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) S TSSOP-EP U28E Maxim Integrated 12

13 MAX179 Revision History REISION NUMBER REISION DATE DESCRIPTION PAGES CHANGED 3 2/15 Updated the Benefits and Features section 1 For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim Integrated s website at. 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. 215 Maxim Integrated Products, Inc. 13