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Part Number MAX1644EAE-T
Manufacturer Maxim Integrated
Datasheet MAX1644EAE-T Datasheet
Package 16-SSOP (0.209", 5.30mm Width)
In Stock 4,656 piece(s)
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Part Number # MAX1644EAE-T (PMIC - Voltage Regulators - DC DC Switching Regulators) is manufactured by Maxim Integrated and distributed by Heisener. Being one of the leading electronics distributors, we carry many kinds of electronic components from some of the world’s top class manufacturers. Their quality is guaranteed by its stringent quality control to meet all required standards.

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MAX1644EAE-T Specifications

ManufacturerMaxim Integrated
CategoryIntegrated Circuits (ICs) - PMIC - Voltage Regulators - DC DC Switching Regulators
Datasheet MAX1644EAE-TDatasheet
Package16-SSOP (0.209", 5.30mm Width)
Output ConfigurationPositive
Output TypeAdjustable (Programmable)
Number of Outputs1
Voltage - Input (Min)3V
Voltage - Input (Max)5.5V
Voltage - Output (Min/Fixed)1.1V (2.525V, 3.33V)
Voltage - Output (Max)5.5V
Current - Output2A
Frequency - SwitchingUp to 350kHz
Synchronous RectifierYes
Operating Temperature-40°C ~ 85°C (TA)
Mounting TypeSurface Mount
Package / Case16-SSOP (0.209", 5.30mm Width)
Supplier Device Package16-SSOP

MAX1644EAE-T Datasheet

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General Description The MAX1644 constant-off-time, PWM step-down DC- DC converter is ideal for use in applications such as PC cards, CPU daughter cards, and desktop computer bus-termination boards. The device features internal synchronous rectification for high efficiency and reduced component count. It requires no external Schottky diode. The internal 0.10Ω PMOS power switch and 0.10Ω NMOS synchronous-rectifier switch easily deliver continuous load currents up to 2A. The MAX1644 produces a preset +3.3V or +2.5V output voltage or an adjustable output from +1.1V to VIN. It achieves efficiencies as high as 95%. The MAX1644 uses a unique current-mode, constant- off-time, PWM control scheme, which includes an Idle Mode™ to maintain high efficiency during light-load operation. The programmable constant-off-time archi- tecture sets switching frequencies up to 350kHz, allow- ing the user to optimize performance trade-offs between efficiency, output switching noise, component size, and cost. The device also features an adjustable soft-start to limit surge currents during start-up, a 100% duty cycle mode for low-dropout operation, and a low- power shutdown mode that disconnects the input from the output and reduces supply current below 1µA. The MAX1644 is available in a 16-pin SSOP package. Applications +5V to +3.3V/+2.5V Conversion CPU I/O Supply +3.3V PC Card and CardBus Applications Notebook and Subnotebook Computers Desktop Bus-Termination Boards CPU Daughter Card Supply Features ♦ ±1% Output Accuracy ♦ 95% Efficiency ♦ Internal PMOS and NMOS Switches 70mΩ On-Resistance at VIN = +4.5V 100mΩ On-Resistance at VIN = +3V ♦ Output Voltage +3.3V or +2.5V Pin-Selectable +1.1V to VIN Adjustable ♦ +3V to +5.5V Input Voltage Range ♦ 360µA (max) Operating Supply Current ♦ < 1µA Shutdown Supply Current ♦ Programmable Constant-Off-Time Operation ♦ 350kHz (max) Switching Frequency ♦ Idle Mode Operation at Light Loads ♦ Thermal Shutdown ♦ Adjustable Soft-Start Inrush Current Limiting ♦ 100% Duty Cycle During Low-Dropout Operation ♦ Output Short-Circuit Protection ♦ 16-Pin SSOP Package M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 SHDN LX PGND LX PGND VCC FBSEL REF GND TOP VIEW MAX1644 SSOP IN LX COMP IN SS TOFF FB A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES. 19-1457; Rev 3; 8/05 Pin Configuration Ordering Information Idle Mode is a trademark of Maxim Integrated Products, Inc. Typical Operating Circuit TOFF COMP VCC FBSEL SHDN IN PGND GND REF SS LX FBMAX1644 RTOFF OUTPUT +1.1V TO VIN INPUT +3V TO +5.5V ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at EVALU ATION KIT AVAIL ABLE PART TEMP RANGE PIN-PACKAGE MAX1644EAE 40°C to +85°C 16 SSOP MAX1644EAE+ 40°C to +85°C 16 SSOP +Denotes lead-free package.

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M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches 2 _______________________________________________________________________________________ ABSOLUTE MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS (VIN = VCC = +3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°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. VCC, IN to GND ........................................................-0.3V to +6V IN to VCC.............................................................................±0.3V GND to PGND.....................................................................±0.3V All Other Pins to GND.................................-0.3V to (VCC + 0.3V) LX Current (Note 1)...........................................................±3.75A REF Short Circuit to GND Duration ............................Continuous ESD Protection .....................................................................±2kV Continuous Power Dissipation (TA = +70°C) SSOP (derate 16.7mW/°C above +70°C; part mounted on 1 in.2 of 1oz. copper) ............................1.2W Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Note 1: LX has internal clamp diodes to PGND and IN. Applications that forward bias these diodes should take care not to exceed the IC’s package power dissipation limits. Hysteresis = 15°C SHDN = GND SHDN = GND ILOAD = 0 to 2A, VFB = VOUT VFB = 1.2V (Note 2) VIN = VCC = 3V, ILOAD = 1A, FBSEL = VCC ILX = 0.5A FBSEL = REF, VCC, or unconnected VIN = VCC = 3V to 5.5V, ILOAD = 0, FBSEL = GND or REF FBSEL = GND IREF = -1µA to +10µA CONDITIONS °C150TSHDN Thermal Shutdown Threshold µA15IIN PMOS Switch Off-Leakage Current µA<1 3ICC(SHDN)Shutdown Supply Current µA240 360IIN + ICCNo-Load Supply Current kHz350fSwitching Frequency A0.25 0.45 0.65IIM Idle Mode Current Threshold A2.5 2.9 3.3ILIMITCurrent-Limit Threshold mΩ 100 200 RON, P PMOS Switch On-Resistance 70 150 mV0.5 1ΔVREFReference Load Regulation 2.500 2.525 2.550 V 3.300 3.333 3.366 V3.0 5.5VIN, VCCInput Voltage V1.089 1.100 1.111VREFReference Voltage mV200VDODropout Voltage % 0.4 1.089 1.100 1.111 VOUTPreset Output Voltage Adjustable Output Voltage Range VVREF VIN 0.2 DC Load Regulation Error UNITSMIN TYP MAXSYMBOLPARAMETER VIN = VCC = 4V to 5.5V, FBSEL = unconnected VIN = VCC = 3V to 5.5V, FBSEL = VCC VIN = VCC = 3V to 5.5V, FBSEL = REF VIN = 4.5V VIN = 3V ILX = 0.5A mΩ 100 200 RON, N NMOS Switch On-Resistance 70 150VIN = 4.5V VIN = 3V FBSEL = GND FBSEL = REF, VCC, or unconnected 1 AC Load Regulation Error % 2 A2.5RMS LX Output Current

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M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches _______________________________________________________________________________________ 3 ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = +3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) ELECTRICAL CHARACTERISTICS (VIN = VCC = +3.3V, FBSEL = GND, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3) Note 2: Recommended operating frequency, not production tested. Note 3: Specifications from 0°C to -40°C are guaranteed by design, not production tested. RTOFF = 150kΩ VFB = 1.2V VFB = 1.2V ILX = 0.5A VIN = 3.0V to 5.5V, ILOAD = 0, FBSEL = GND or REF ILX = 0.5A CONDITIONS µs1.03 1.63tOFFOff-Time Default Period nA0 250IFBFB Input Bias Current µA360IIN + ICCNo-Load Supply Current A0.2 0.7IIM Idle Mode Current Threshold A2.3 3.5ILIMITCurrent-Limit Threshold mΩ 200 RON, P PMOS Switch On-Resistance mΩ 150 200 RON, N 2.48 2.57 3.276 3.390 V3.0 5.5VINInput Voltage V1.08 1.12VREFReference Voltage VVREF VINAdjustable Output Voltage 1.08 1.12 UNITSMIN TYP MAXSYMBOLPARAMETER VIN = VCC = 4V to 5.5V, FBSEL = unconnected VIN = 3V to 5.5V, FBSEL = VCC VIN = 3V to 5.5V, FBSEL = REF VIN = 4.5V VIN = 3V NMOS Switch On-Resistance 150VIN = 4.5V VIN = 3V V ILOAD = 0 to 2A, VFB = VOUT VOUTPreset Output Voltage Maximum Output RMS Current ARMS SS Sink Current ISS 100 µA SHDN Input Current ISHDN -0.5 0.5 µA SS Source Current ISS 3.5 5 6.5 µA SHDN Input Low Threshold VIL 0.8 V SHDN Input High Threshold VIH 2.0 V FBSEL Input Current -5 +5 µA 0.9 1.3 5.8 VSS = 1V V SHDN = 0 to VCC FBSEL = REF PARAMETER SYMBOL MIN TYP MAX UNITS Undervoltage Lockout Threshold VUVLO 2.5 2.6 2.7 V FB Input Bias Current IFB 0 80 200 nA tOFF 1.13 1.33 1.53 0.20 0.33 Off-Time Start-Up Period tOFF 4 · tOFF µs On-Time Period tON 0.4 µs CONDITIONS VFB = 1.2V RTOFF = 150kΩ RTOFF = 30.1kΩ VIN falling, hysteresis = 40mV FB = GND Off-Time Default Period 4.3 5.6 µs RTOFF = 499kΩ FBSEL Logic Thresholds 0.2 V FBSEL = GND 0.7 · VCC 0.7 · VCC - 0.2 + 0.2 FBSEL = unconnected VCC - 0.2FBSEL = VCC

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M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches 4 _______________________________________________________________________________________ Typical Operating Characteristics (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) 1 10 0 10 30 20 40 50 70 60 80 90 100 0.001 0.01 0.1 EFFICIENCY vs. OUTPUT CURRENT M A X 1 6 4 4 -0 1 OUTPUT CURRENT (A) EF FI C IE N C Y ( % ) VIN = 5V, VOUT = 3.3V, L = 6.0μH, RTOFF = 120kΩ 100 1 10 0 10 30 20 40 50 70 60 80 90 0.001 0.01 0.1 EFFICIENCY vs. OUTPUT CURRENT M A X 1 6 4 4 -0 2 OUTPUT CURRENT (A) EF FI C IE N C Y ( % ) VIN = 3.3V, VOUT = 1.5V, L = 4.7μH, RTOFF = 200kΩ VIN = 5V, VOUT = 1.5V, L = 6.0μH, RTOFF = 270kΩ 1 10 -1.0 -0.9 -0.7 -0.8 -0.6 -0.5 -0.3 -0.4 -0.2 -0.1 0 0.0001 0.001 0.01 0.1 DC LOAD-REGULATION ERROR vs. OUTPUT CURRENT M A X 1 6 4 4 -0 3 OUTPUT CURRENT (A) D C L O A D -R EG U LA TI O N E R R O R ( % ) A B E C D A: VIN = 3.3V, VOUT = 1.5V, L = 4.7μH, RTOFF = 200kΩ, FBSEL = GND B: VIN = 3.3V, VOUT = 1.5V, L = 4.7μH, RTOFF = 200kΩ, FBSEL = REF C: VIN = 5V, VOUT = 3.3V, L = 6.0μH, RTOFF = 120kΩ, FBSEL = OPEN D: VIN = 5V, VOUT = 1.5V, L = 6.0μH, RTOFF = 270kΩ, FBSEL = GND E: VIN = 5V, VOUT = 1.5V, L = 6.0μH, RTOFF = 270kΩ, FBSEL = REF 0 100 50 250 200 150 300 350 0 1.00.5 1.5 2.0 SWITCHING FREQUENCY vs. OUTPUT CURRENT M A X 1 6 4 4 -0 4 OUTPUT CURRENT (A) S W IT C H IN G F R EQ U EN C Y ( kH z) VIN = 3.3V, VOUT = 1.5V, L = 4.7μH, RTOFF = 200kΩ VIN = 5V, VOUT = 1.5V, L = 6.0μH, RTOFF = 270kΩ VIN = 5V, VOUT = 3.3V, L = 6.0μH, RTOFF = 120kΩ 0 150 100 50 200 250 300 350 400 450 500 0 21 3 4 5 6 SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1644-07 SUPPLY VOLTAGE S U P P LY C U R R EN T I C C (μ A ) 0 0.03 0.02 0.01 0.04 0.05 0.06 0.07 0.08 0.09 0.10 S H U TD O W N S U P P LY C U R R EN T I IN + I C C ( μ A ) IOUT = 0 UNDERVOLTAGE LOCKOUT SHDN = VIN = VCC SHDN = GND 0 1.0 0.5 2.5 2.0 1.5 4.0 3.5 3.0 4.5 0 200100 300 400 500 600 OFF-TIME vs. RTOFF M A X 1 6 4 4 -0 6 RTOFF (kΩ) t O FF ( μ s) VSHDN 5V/div IIN 1A/div 0 0 VOUT 2V/div VSS 1V/div 0 0 2ms/div STARTUP AND SHUTDOWN TRANSIENTS M A X 1 6 4 4 -0 9 VIN = 5.0V, VOUT = 3.3V, IOUT = 2A

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M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches _______________________________________________________________________________________ 5 Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) NAME FUNCTION 1 SHDN Shutdown Control Input. Drive SHDN low to disable the reference, control circuitry, and internal MOSFETs. Drive high or connect to VCC for normal operation. PIN Pin Description VIN VOUT 20mV/div 4V 3V 20μs/div LINE-TRANSIENT RESPONSE M A X 1 6 4 4 -1 0 VOUT = 1.5V, IOUT = 2A IL VOUT 50mV/div 2A 0 20μs/div LOAD-TRANSIENT RESPONSE (FBSEL = REF) M A X 1 6 4 4 -1 1 VIN = 3.3V, VOUT = 1.5V 2, 4 IN Supply Voltage Input for the internal PMOS power switch 3, 14, 16 LX Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch. Connect the inductor from this node to output filter capacitor and load. 5 SS Soft-Start. Connect a capacitor from SS to GND to limit inrush current during start-up. 6 COMP Integrator Compensation. Connect a capacitor from COMP to VCC for integrator compensation. See the Integrator Amplifier section. 7 TOFF Off-Time Select Input. Sets the PMOS power switch off-time during constant-off-time operation. Connect a resistor from TOFF to GND to adjust the PMOS switch off-time. 8 FB Feedback Input for both preset-output and adjustable-output operating modes. Connect directly to output for fixed-voltage operation or to a resistor-divider for adjustable operating modes. 9 GND Analog Ground 10 REF Reference Output. Bypass REF to GND with a 1µF capacitor. 11 FBSEL Feedback Select Input. Selects AC load-regulation error and output voltage. See Table 2 for program- ming instructions. 12 VCC Analog Supply Voltage Input. Supplies internal analog circuitry. Bypass VCC with a 10Ω and 2.2µF low- pass filter. See Figure 1. 13, 15 PGND Power Ground. Internally connected to the internal NMOS synchronous-rectifier switch.

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M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches 6 _______________________________________________________________________________________ _______________Detailed Description The MAX1644 synchronous, current-mode, constant-off- time, PWM DC-DC converter steps down input voltages of +3V to +5.5V to a preset output voltage of either +3.3V or +2.5V, or to an adjustable output voltage from +1.1V to VIN. The device delivers up to 2A of continuous load current. Internal switches composed of a 0.1Ω PMOS power switch and a 0.1Ω NMOS synchronous-rectifier switch improve efficiency, reduce component count, and eliminate the need for an external Schottky diode. The MAX1644 optimizes performance by operating in constant-off-time mode under heavy loads and in Maxim’s proprietary Idle Mode under light loads. A sin- gle resistor-programmable constant-off-time control sets switching frequencies up to 350kHz, allowing the user to optimize performance trade-offs in efficiency, switching noise, component size, and cost. Under low- dropout conditions, the device operates in a 100% duty-cycle mode, where the PMOS switch remains per- manently on. Idle Mode enhances light-load efficiency by skipping cycles, thus reducing transition and gate- charge losses. When power is drawn from a regulated supply, constant- off-time PWM architecture essentially provides constant- frequency operation. This architecture has the inherent advantage of quick response to line and load transients. The MAX1644’s current-mode, constant-off-time PWM architecture regulates the output voltage by changing the PMOS switch on-time relative to the constant off- time. Increasing the on-time increases the peak induc- tor current and the amount of energy transferred to the load per pulse. Modes of Operation The current through the PMOS switch determines the mode of operation: constant-off-time mode (for load currents greater than 0.2A) or Idle Mode (for load cur- rents less than 0.2A). Current sense is achieved through a proprietary architecture that eliminates cur- rent-sensing I2R losses. Constant-Off-Time Mode Constant-off-time operation occurs when the current through the PMOS switch is greater than the Idle Mode threshold current (0.4A, which corresponds to a load current of 0.2A). In this mode, the regulation compara- tor turns the PMOS switch on at the end of each off- time, keeping the device in continuous-conduction mode. The PMOS switch remains on until the output is in regulation or the current limit is reached. When the PMOS switch turns off, it remains off for the pro- grammed off-time (tOFF). If the output falls dramatically out of regulation—approximately VFB / 4—the PMOS switch remains off for approximately four times tOFF. The NMOS synchronous rectifier turns on shortly after the PMOS switch turns off, and it remains on until short- ly before the PMOS switch turns back on. Idle Mode Under light loads, the device improves efficiency by switching to a pulse-skipping Idle Mode. Idle Mode operation occurs when the current through the PMOS switch is less than the Idle Mode threshold current. Idle Mode forces the PMOS to remain on until the current through the switch reaches 0.4A, thus minimizing the unnecessary switching that degrades efficiency under light loads. In Idle Mode, the device operates in discon- tinuous conduction. Current-sense circuitry monitors the current through the NMOS synchronous switch, turning it off before the current reverses. This prevents current from being pulled from the output filter through the inductor and NMOS switch to ground. As the device switches between operating modes, no major shift in cir- cuit behavior occurs. 100% Duty-Cycle Operation When the input voltage drops near the output voltage, the duty cycle increases until the PMOS MOSFET is on continuously. The dropout voltage in 100% duty cycle is the output current multiplied by the on-resistance of the internal PMOS switch and parasitic resistance in the inductor. The PMOS switch remains on continuously as long as the current limit is not reached. Shutdown Drive SHDN to a logic-level low to place the MAX1644 in low-power shutdown mode and reduce supply cur- rent to less than 1µA. In shutdown, all circuitry and internal MOSFETs turn off, and the LX node becomes high impedance. Drive SHDN to a logic-level high or connect to VCC for normal operation. Summing Comparator Three signals are added together at the input of the summing comparator (Figure 1): an output voltage error signal relative to the reference voltage, an integrated output voltage error correction signal, and the sensed PMOS switch current. The integrated error signal is pro- vided by a transconductance amplifier with an external capacitor at COMP. This integrator provides high DC accuracy without the need for a high-gain amplifier. Connecting a capacitor at COMP modifies the overall loop response (see the Integrator Amplifier section).

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Synchronous Rectification In a step-down regulator without synchronous rectifica- tion, an external Schottky diode provides a path for cur- rent to flow when the inductor is discharging. Replacing the Schottky diode with a low-resistance NMOS syn- chronous switch reduces conduction losses and improves efficiency. The NMOS synchronous-rectifier switch turns on follow- ing a short delay after the PMOS power switch turns off, thus preventing cross conduction or “shoot through.” In constant-off-time mode, the synchronous-rectifier switch turns off just prior to the PMOS power switch turning on. While both switches are off, inductor current flows through the internal body diode of the NMOS switch. The internal body diode’s forward voltage is rel- atively high. Thermal Resistance Junction-to-ambient thermal resistance, θJA, is highly dependent on the amount of copper area immediately surrounding the IC leads. The MAX1644 evaluation kit has 0.5 in.2 of copper area and a thermal resistance of 60°C/W with no airflow. Airflow over the IC significantly reduces the junction-to-ambient thermal resistance. For heatsinking purposes, evenly distribute the copper area connected at the IC among the high-current pins. Power Dissipation Power dissipation in the MAX1644 is dominated by conduction losses in the two internal power switches. Power dissipation due to supply current in the control section and average current used to charge and dis- charge the gate capacitance of the internal switches are less than 30mW at 300kHz. This number is reduced when the switching frequency decreases as the part enters Idle Mode. Combined conduction losses in the two power switches are approximated by: PD = IOUT2 · RON The junction-to-ambient thermal resistance required to dissipate this amount of power is calculated by: θJA = (TJ,MAX - TA,MAX) / PD where: θJA = junction-to-ambient thermal resistance TJ,MAX = maximum junction temperature TA,MAX = maximum ambient temperature M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches _______________________________________________________________________________________ 7 MAX1644 VCC 470pF 2.2μF 1μF 10μF 10Ω FBSEL 0.01μF FEEDBACK SELECTION CURRENT SENSE PWM LOGIC AND DRIVERS SS IN FB VIN 3.0V TO 5.5V LX PGNDTOFF RTOFF GND NOTE: HEAVY LINES DENOTE HIGH-CURRENT PATHS. REF REF SUMMING COMPARATOR REF REF COMP SKIP SHDN TIMER VIN CURRENT SENSE Gm COUT VOUT Figure 1. Functional Diagram

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M A X 1 6 4 4 __________________Design Procedure For typical applications, use the recommended compo- nent values in Table 1. For other applications, take the following steps: 1) Select the desired PWM-mode switching frequency; 300kHz is a good starting point. 2) Select the constant-off-time as a function of input voltage, output voltage, and switching frequency. 3) Select RTOFF as a function of off-time. 4) Select the inductor as a function of output voltage, off-time, and peak-to-peak inductor current. Setting the Output Voltage The output of the MAX1644 is selectable between one of two preset output voltages: (2.5V or 3.3V) with a 2% AC load-regulation error, or an adjustable output volt- age from the reference voltage (nominally 1.1V) up to VIN with a 1% or 2% AC load-regulation error. For a preset output voltage, connect FB to the output voltage, and connect FBSEL to VCC (2.5V output voltage) or leave unconnected (3.3V output voltage). Internal resis- tor-dividers divide down the output voltage, regulating the divided voltage to the internal reference voltage. For output voltages other than 2.5V or 3.3V, or for tighter AC load regulation, connect FBSEL to GND (1% regulation) or to REF (2% regulation), and connect FB to a resistor divider between the output voltage and ground (Figure 2). Regulation is maintained for adjustable output voltages when VFB equals VREF. Use 50kΩ for R1. R2 is given by the equation: where VREF is typically 1.1V. Programming the Switching Frequency and Off-Time The MAX1644 features a programmable PWM mode switching frequency, which is set by the input and out- put voltage and the value of RTOFF, connected from TOFF to GND. RTOFF sets the PMOS power switch off- time in PWM mode. Use the following equation to select the off-time according to your desired switching fre- quency in PWM mode (IOUT > 0.2A): where: tOFF = the programmed off-time VIN = the input voltage VOUT = the output voltage VNMOS = the voltage drop across the internal PMOS power switch VPMOS = the voltage drop across the internal NMOS synchronous-rectifier switch t V V V f V V V OFF IN OUT PMOS PWM IN PMOS NMOS – = −( ) − +( ) R2 R1 V V 1OUT REF = − ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches 8 _______________________________________________________________________________________ VOUT (V) RTOFF (kΩ) 6.0 120 L (µH) 5 3.3 6.8 VIN (V) 180 6.8 2405 1.8 3.3 823.3 2.5 4.7 1803.3 1.8 4.7 2003.3 1.5 5 2.5 Table 2. Output Voltage and AC Load- Regulation Selection PIN 2.5 2VCC Output Voltage 3.3 2 Adjustable 2REF Resistor Divider Adjustable 1GND Resistor Divider Unconnected Output Voltage FB AC LOAD- REGULATION ERROR (%) OUTPUT VOLTAGE (V)FBSEL LX R2 R1 R1 = 50kΩ R2 = R1(VOUT / VREF - 1) VREF = 1.1V FB VOUT MAX1644 Figure 2. Adjustable Output Voltage Table 1. Recommended Component Values (IOUT = 2A, fPWM = 300kHz) 6.0 2705 1.5

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fPWM = switching frequency in PWM mode (IOUT > 0.2A) Select RTOFF according to the formula: RTOFF = (tOFF - 0.07µs) (150kΩ / 1.26µs) Recommended values for RTOFF range from 39kΩ to 470kΩ for off-times of 0.4µs to 4µs. Inductor Selection Three key inductor parameters must be specified: inductor value (L), peak current (IPEAK), and DC resis- tance (RDC). The following equation includes a con- stant, denoted as LIR, which is the ratio of peak- to-peak inductor AC current (ripple current) to maxi- mum DC load current. A higher value of LIR allows smaller inductance but results in higher losses and rip- ple. A good compromise between size and losses is found at approximately a 25% ripple-current to load- current ratio (LIR = 0.25), which corresponds to a peak inductor current 1.125 times higher than the DC load current: where: IOUT = maximum DC load current LIR = ratio of peak-to-peak AC inductor current to DC load current, typically 0.25 The peak inductor current at full load is 1.125 · IOUT if the above equation is used; otherwise, the peak current is calculated by: Choose an inductor with a saturation current at least as high as the peak inductor current. To minimize loss, choose an inductor with a low DC resistance. Capacitor Selection The input filter capacitor reduces peak currents and noise at the voltage source. Use a low-ESR and low- ESL capacitor located no further than 5mm from IN. Select the input capacitor according to the RMS input ripple-current requirements and voltage rating: The output filter capacitor affects the output voltage rip- ple, output load-transient response, and feedback loop stability. For stable operation, the MAX1644 requires a minimum output ripple voltage of VRIPPLE ≥ 2% · VOUT (with 2% load regulation setting). The minimum ESR of the output capacitor should be: Stable operation requires the correct output filter capacitor. When choosing the output capacitor, ensure that: COUT ≥ (tOFF / VOUT) ✕ (64µFV / µs) With an AC load regulation setting of 1%, the COUT requirement doubles, and the minimum ESR of the out- put capacitor is halved. Integrator Amplifier An internal transconductance amplifier fine tunes the output DC accuracy. A capacitor, CCOMP, from COMP to VCC compensates the transconductance amplifier. For stability, choose: CCOMP ≥ 470pF A large capacitor value maintains a constant average output voltage but slows the loop response to changes in output voltage. A small capacitor value speeds up the loop response to changes in output voltage but decreases stability. Choose the capacitor values that result in optimal performance. Setting the AC Loop Gain The MAX1644 allows selection of a 1% or 2% AC load- regulation error when the adjustable output voltage mode is selected (Table 2). A 2% setting is automati- cally selected in preset output voltage mode (FBSEL connected to VCC or unconnected). A 2% load-regula- tion error setting reduces output filter capacitor require- ments, allowing the use of smaller and less expensive capacitors. Selecting a 1% load-regulation error reduces transient load errors, but requires larger capac- itors. ESR L tOFF % > ×1 I I V V V V RIPPLE LOAD OUT IN OUT IN = −( ) I I V t L PEAK OUT OUT OFF = + × ×2 L V t I LIR OUT OFF OUT = × × M A X 1 6 4 4 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches _______________________________________________________________________________________ 9

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May 29, 2020

These are a great value at this price.


May 24, 2020

Great product at a good price. No complaints.


May 18, 2020

Items arrived well pakaged, reasonable postage and as described. Top seller


May 14, 2020

Heisener parametric search for specific components is by far better than their competitors.


May 7, 2020

fast delivery and good product, very happy


May 5, 2020

All items individually packed in anti static bags and properly labeled.


April 24, 2020

Easy to browse and order. You have everything I want. I compared the prices and services with others and found you're the best choice.

Ali***** Mody

April 21, 2020

Excellent sales and service. Thank you. Buy with confidence.


April 17, 2020

They work great exactly what I needed.


April 14, 2020

I always enjoy shopping with Heisener, never makes a mistake, most reliable, and no long waiting for deliveries.

MAX1644EAE-T Guarantees

Service Guarantee

Service Guarantees

We guarantee 100% customer satisfaction.

Our experienced sales team and tech support team back our services to satisfy all our customers.

Quality Guarantee

Quality Guarantees

We provide 90 days warranty.

If the items you received were not in perfect quality, we would be responsible for your refund or replacement, but the items must be returned in their original condition.

MAX1644EAE-T Packaging

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Certified Quality

Heisener's commitment to quality has shaped our processes for sourcing, testing, shipping, and every step in between. This foundation underlies each component we sell.

ISO9001:2015, ICAS, IAF, UKAS

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