MAX1644EAE ,2A, low-voltage, step-down regulator with synchronous rectification and intemal switchesfeatures internal' Internal PMOS and NMOS Switchessynchronous rectification for high efficiency and ..
MAX1644EAE+ ,2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal SwitchesFeaturesThe MAX1644 constant-off-time, PWM step-down DC- ±1% Output AccuracyDC converter is ideal ..
MAX1644EAE+T ,2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal SwitchesMAX164419-1457; Rev 2; 3/022A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and I ..
MAX1644EAE-T ,2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal SwitchesELECTRICAL CHARACTERISTICS (continued)(V = V = +3.3V, FBSEL = GND, T = 0°C to +85°C, unless otherwi ..
MAX1645A ,Advanced-Chemistry-Independent, Level-2 Battery Chargers with Input Current LimitingELECTRICAL CHARACTERISTICS(Circuit of Figure 1, V = +3.3V, V = +16.8V, V = +18V, T = 0°C to +85°C, ..
MAX1645AEEI ,Advanced Chemistry-Independent / Level 2 Battery Chargers with Input Current LimitingFeaturesThe MAX1645 are high-efficiency battery chargers capa- Input Current Limitingble of chargi ..
MAX4394ESD ,Ultra-Small / Low-Cost / 85MHz Op Amps with Rail-to-Rail Outputs and DisableFeaturesThe MAX4389/MAX4390/MAX4392–MAX4396 family of Low Costop amps are unity-gain stable devic ..
MAX4394EUD ,Ultra-Small / Low-Cost / 85MHz Op Amps with Rail-to-Rail Outputs and Disableapplications). The MAX4389/MAX4390/ Low Differential Gain/Phase: 0.015%/0.015°MAX4392–MAX4396 cons ..
MAX4394EUD+ ,Ultra-Small, Low-Cost, 85MHz Op Amps with Rail-to-Rail Outputs and DisableElectrical Characteristics—Single Supply (continued)(V = 5V, V = 0V, V = V /2, V = V /2, R = ∞ to V ..
MAX4394EUD+T ,Ultra-Small, Low-Cost, 85MHz Op Amps with Rail-to-Rail Outputs and DisableFeatures● Low CostThe MAX4389/MAX4390/MAX4392–MAX4396 family of op amps are unity-gain stable devic ..
MAX4394EUD+T ,Ultra-Small, Low-Cost, 85MHz Op Amps with Rail-to-Rail Outputs and DisableFeatures● Low CostThe MAX4389/MAX4390/MAX4392–MAX4396 family of op amps are unity-gain stable devic ..
MAX4395ESD ,Ultra-Small / Low-Cost / 85MHz Op Amps with Rail-to-Rail Outputs and DisableApplications Ordering InformationSet-Top BoxesPIN- TOPPART TEMP RANGEPACKAGE MARKSurveillance Video ..
MAX1644EAE
2A, low-voltage, step-down regulator with synchronous rectification and intemal switches
General DescriptionThe 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 0.10ΩPMOS power switch
and 0.10ΩNMOS 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 Accuracy95% EfficiencyInternal PMOS and NMOS Switches
70mΩOn-Resistance at VIN= +4.5V
100mΩOn-Resistance at VIN= +3VOutput Voltage
+3.3V or +2.5V Pin-Selectable
+1.1V to VINAdjustable+3V to +5.5V Input Voltage Range360µA (max) Operating Supply Current< 1µA Shutdown Supply CurrentProgrammable Constant-Off-Time Operation350kHz (max) Switching FrequencyIdle Mode Operation at Light LoadsThermal Shutdown Adjustable Soft-Start Inrush Current Limiting100% Duty Cycle During Low-Dropout OperationOutput Short-Circuit Protection16-Pin SSOP Package
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
Pin Configuration
Ordering Information
Typical Operating Circuit
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
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
LX to PGND.................................................-0.3V to (VIN+ 0.3V)
All Other Pins to GND.................................-0.3V to (VCC+ 0.3V)
Continuous LX Output Current..............................................2.5A
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.2of 1oz. copper)............................1.2W
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10sec)............................+300°C
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
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 2)
Note 1:Recommended operating frequency, not production tested.
Note 2:Specifications from 0°C to -40°C are guaranteed by design, not production tested.
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
Typical Operating Characteristics(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switchesypical Operating Characteristics (continued)(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
Pin Description
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
_______________Detailed DescriptionThe 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 0.1ΩPMOS
power switch and a 0.1ΩNMOS 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 OperationThe 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 ModeConstant-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 ModeUnder 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 OperationWhen 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.
ShutdownDrive SHDNto 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 SHDNto a logic-level high or
connect to VCCfor normal operation.
Summing ComparatorThree 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 Integrator Amplifier section).
