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MAX4372FEUK+ ,Low-Cost, UCSP/SOT23, Micropower, High-Side Current-Sense Amplifier with Voltage OutputApplications+Denotes lead(Pb)-free/RoHS-compliant package.● Power-Management SystemsT = Tape and re ..
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MAX4372HESA ,Low-Cost, SOT23, Micropower, High-Side Current-Sense Amplifier with Voltage OutputApplicationsMAX4372FEUK-T -40°C to +85°C 5 SOT23-5 ADIVMAX4372FESA -40°C to +85°C 8 SO —Power-Manag ..
MAX1626ESA-MAX1627ESA
5V/3.3V or Adjustable / 100% Duty-Cycle / High-Efficiency / Step-Down DC-DC Controllers
_______________General DescriptionThe MAX1626/MAX1627 step-down DC-DC switching
controllers provide high efficiency over loads ranging
from 1mA to more than 2A. A unique current-limited,
pulse-frequency-modulated (PFM) control scheme
operates with up to a 100% duty cycle, resulting in very
low dropout voltages. This control scheme eliminates
minimum load requirements and reduces the supply
current under light loads to 90µA (versus 2mA to 10mA
for common pulse-width modulation controllers).
These step-down controllers drive an external P-chan-
nel MOSFET, allowing design flexibility for applications
to 12W or higher. Soft-start reduces current surges dur-
ing start-up. A high switching frequency (up to 300kHz)
and operation in continuous-conduction mode allow the
use of tiny surface-mount inductors. Output capacitor
requirements are also reduced, minimizing PC board
area and system costs.
The output voltage is preset at 5V or 3.3V for the
MAX1626 and adjustable for the MAX1627. Input volt-
ages can be up to 16.5V. The MAX1626/MAX1627 are
functional upgrades for the MAX1649/MAX1651.
________________________ApplicationsPCMCIA Power Supplies
Personal Digital Assistants
Hand-Held Computers
Portable Terminals
Low-Cost Notebook Computer Supplies
5V to 3.3V Green PC Applications
High-Efficiency Step-Down Regulation
Minimum-Component DC-DC Converters
Battery-Powered Applications
____________________________FeaturesLow Dropout Voltage100% Maximum Duty CycleSoft-Start Limits Start-Up CurrentEfficiency >90% (3mA to 2A Loads)Output Power >12.5W90µA Max Quiescent Current1µA Max Shutdown CurrentUp to 300kHz Switching Frequency16.5V Max Input VoltageOutput Voltage: 5V/3.3V (MAX1626)
Adjustable (MAX1627)Current-Limited Control Scheme
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
________________________________________________________________Maxim Integrated Products1
__________________Pin Configuration
__________Typical Operating Circuit
& the latest literature: http://,
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(V+ = +3V to +16.5V, SHDN = 3/5 = 0V, TA= 0°C to +85°C, unless otherwise noted.)
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.
Supply Voltage, V+ to GND.......................................-0.3V, +17V
OUT, FB, 3/5, SHDN, REF, CS, EXT to GND...-0.3V, (V+ + 0.3V)
Maximum Current at REF (IREF)..........................................15mA
Maximum Current at EXT (IEXT)..........................................50mA
Continuous Power Dissipation (TA= +70°C)
SO (derate 5.88mW/°C above +70°C)..........................471mW
Operating Temperature Range
MAX1626ESA/MAX1627ESA............................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
_______________________________________________________________________________________3
ELECTRICAL CHARACTERISTICS(V+ = +3V to +16.5V, SHDN = 3/5 = 0V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
Note 1:V+ must exceed VOUTto maintain regulation.
Note 2:Specifications from 0°C to -40°C are guaranteed by design, not production tested.
__________________________________________Typical Operating Characteristics(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
0.1m100m11m10m10
EFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)MAX1626-05
LOAD CURRENT (A)
EFFICIENCY (%)40
0.1m100m11m10m10
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5V)MAX1626-03
LOAD CURRENT (A)
EFFICIENCY (%)40
DROPOUT VOLTAGE
vs. LOAD CURRENT
MAX1626-11
LOAD (A)
DROPOUT VOLTAGE (V)
0.15
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
MAX1626 SHUTDOWN CURRENT
vs. TEMPERATURE
MAX1626-04
TEMPERATURE (°C)
SHUTDOWN CURRENT (
EXT RISE AND FALL TIMES
vs. CAPACITANCE
MAX1626-10
CAPACITANCE (pF)
tRISE
AND t
FALL
(ns)
EXT RISE AND FALL TIMES
vs. TEMPERATURE
MAX1626-09
TEMPERATURE (°C)
tRISE
AND t
FALL
(ns)2080
MAX1626
V+ QUIESCENT CURRENT
vs. TEMPERATURE
MAX1626-01
TEMPERATURE (°C)
IQ (
MAX1626 EXT OFF TIME
vs. OUTPUT VOLTAGE
MAX1626-02
OUTPUT VOLTAGE (V)
EXT OFF TIME (
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
_______________________________________________________________________________________5REFERENCE OUTPUT VOLTAGE
vs. TEMPERATURE
MAX1626-13
TEMPERATURE (°C)
REFERENCE OUTPUT VOLTAGE (V)
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA= +25°C, unless otherwise noted.)
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers_______________________________________________________________________________________
______________________________________________________________Pin DescriptionFigure 1. MAX1626 Typical Operating Circuit
MAX1626/MAX1627
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
_______________________________________________________________________________________7
_______________Detailed DescriptionThe MAX1626/MAX1627 are step-down DC-DC con-
trollers designed primarily for use in portable comput-
ers and battery-powered devices. Using an external
MOSFET and current-sense resistor allows design flexi-
bility and the improved efficiencies associated with
high-performance P-channel MOSFETs. A unique, cur-
rent-limited, pulse-frequency-modulated (PFM) control
scheme gives these devices excellent efficiency over
load ranges up to three decades, while drawing around
90µA under no load. This wide dynamic range opti-
mizes the MAX1626/MAX1627 for battery-powered
applications, where load currents can vary consider-
ably as individual circuit blocks are turned on and off to
conserve energy. Operation to a 100% duty cycle
allows the lowest possible dropout voltage, extending
battery life. High switching frequencies and a simple
circuit topology minimize PC board area and compo-
nent costs. Figure 1 shows a typical operating circuit
for the MAX1626.
PFM Control SchemeThe MAX1626/MAX1627 use a proprietary, third-genera-
tion, current-limited PFM control scheme. Improvements
include a reduced current-sense threshold and operation
to a 100% duty cycle. These devices pulse only as need-
ed to maintain regulation, resulting in a variable switching
frequency that increases with the load. This eliminates the
current drain associated with constant-frequency pulse-
width-modulation (PWM) controllers, caused by switching
the MOSFET unnecessarily.
When the output voltage is too low, the error compara-
tor sets a flip-flop, which turns on the external P-chan-
nel MOSFET and begins a switching cycle (Figures 1
and 2). As shown in Figure 3, current through the
inductor ramps up linearly, storing energy in a magnet-
ic field while dumping charge into an output capacitor
and servicing the load. When the MOSFET is turned off,
the magnetic field collapses, diode D1 turns on, and
the current through the inductor ramps back down,
transferring the stored energy to the output capacitor
and load. The output capacitor stores energy when the
inductor current is high and releases it when the induc-
tor current is low.
The MAX1626/MAX1627 use a unique feedback and
control system to govern each pulse. When the output
voltage is too low, the error comparator sets a flip-flop,
which turns on the external P-channel MOSFET. The
MOSFET turns off when the current-sense threshold is
exceeded or when the output voltage is in regulation. A
one-shot enforces a 2µs minimum on-time, except in
current limit. The flip-flop resets when the MOSFET
turns off. Otherwise the MOSFET remains on, allowing a
duty cycle of up to 100%. This feature ensures the low-
est possible dropout. Once the MOSFET is turned off,
the minimum off-time comparator keeps it off. The mini-
mum off-time is normally 2µs, except when the output is
significantly out of regulation. If the output is low by
30% or more, the minimum off-time increases, allowing
soft-start. The error comparator has 0.5% hysteresis for
improved noise immunity.
In the MAX1626, the 3/5 pin selects the output voltage
(Figure 2). In the MAX1627, external feedback resistors
at FB adjust the output.
Operating ModesWhen delivering low and medium output currents, the
MAX1626/MAX1627 operate in discontinuous-conduc-
tion mode. Current through the inductor starts at zero,
rises as high as the peak current limit set by the cur-
rent- sense resistor, then ramps down to zero during
each cycle (Figure 3). Although efficiency is still excel-
lent, output ripple increases and the switch waveform
exhibits ringing. This ringing occurs at the resonant fre-
quency of the inductor and stray capacitance, due to
residual energy trapped in the core when the commuta-
tion diode (D1 in Figure 1) turns off. It is normal and
poses no operational problems.
When delivering high output currents, the MAX1626/
MAX1627 operate in continuous-conduction mode
(Figure 4). In this mode, current always flows through
the inductor and never ramps to zero. The control cir-
cuit adjusts the switch duty cycle to maintain regulation
without exceeding the peak switching current set by
the current-sense resistor. This provides reduced out-
put ripple and high efficiency.
100% Duty Cycle and DropoutThe MAX1626/MAX1627 operate with a duty cycle up
to 100%. This feature extends usable battery life by
turning the MOSFET on continuously when the supply
voltage approaches the output voltage. This services
the load when conventional switching regulators with
less than 100% duty cycle would fail. Dropout voltage
is defined as the difference between the input and out-
put voltages when the input is low enough for the out-
put to drop out of regulation. Dropout depends on the
MOSFET drain-to-source on-resistance, current-sense
resistor, and inductor series resistance, and is propor-
tional to the load current:
MAX1626/MAX1627
EXT Drive Voltage RangeEXT swings from V+ to GND and provides the gate
drive for an external P-channel power MOSFET. A high-
er supply voltage increases the gate drive to the
MOSFET and reduces on-resistance (RDS(ON)). See
External Switching Transistorsection.
Quiescent CurrentThe device’s typical quiescent current is 70µA.
However, actual applications draw additional current to
supply MOSFET switching currents, OUT pin current, or
external feedback resistors (if used), and both the diode
and capacitor leakage currents. For example, in the cir-
cuit of Figure 1, with V+ at 7V and VOUTat 5V, typical
no-load supply current for the entire circuit is 84µA.
When designing a circuit for high-temperature opera-
tion, select a Schottky diode with low reverse leakage.
Shutdown ModeWhen SHDN is high, the device enters shutdown mode.
In this mode, the feedback and control circuit, reference,
and internal biasing circuitry are turned off. EXT goes
high, turning off the external MOSFET. The shutdown
supply current drops to less than 1µA. SHDN is a logic-
level input. Connect SHDN to GND for normal operation.
ReferenceThe 1.3V reference is suitable for driving external loads,
such as an analog-to-digital converter. It has a guaran-
teed 10mV maximum load regulation while sourcing load
currents up to 100µA. The reference is turned off during
shutdown. Bypass the reference with 0.1µF for normal
operation. Place the bypass capacitor within 0.2 inches
(5mm) of REF, with a direct trace to GND (Figure 7).
Soft-StartSoft-start reduces stress and transient voltage slumps
on the power source. When the output voltage is near
ground, the minimum off-time is lengthened to limit peak
switching current. This compensates for reduced nega-
tive inductor current slope due to low output voltages.
________________Design Information
Setting the Output VoltageThe MAX1626’s output voltage can be selected to 3.3V
or 5V under logic control by using the 3/5 pin. The 3/5
pin requires less than 0.5V to ensure a 3.3V output, or
more than (V+ - 0.5)V to guarantee a 5V output. The
voltage sense pin (OUT) must be connected to the out-
put for the MAX1626.
The MAX1627’s output voltage is set using two resis-
tors, R2 and R3 (Figure 5), which form a voltage divider
between the output and GND. R2 is given by:
where VREF= 1.3V. Since the input bias current at FB
has a maximum value of 50nA, large values (10kΩto
200kΩ) can be used for R3 with no significant accuracy
loss. For 1% error, the current through R2 should be at
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers_______________________________________________________________________________________Figure 3. Discontinuous-Conduction Mode, Light-Load-Current
Waveform
Figure 4. Continuous-Conduction Mode, Heavy-Load-Current
Waveform
