MAX1745AUB+ ,High-Voltage, Step-Down DC-DC Controller in µMAXELECTRICAL CHARACTERISTICS(V = V = 5.5V to 36V, 3/5 = GND, I = 0, T = 0°C to +85°C, unless otherwis ..
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MAX1745EUB ,High-Voltage, Step-Down DC-DC Controller in レMAXGeneral Description ________
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MAX4581ASE ,Low-Voltage, CMOS Analog Multiplexers/SwitchesFeaturesThe MAX4581/MAX4582/MAX4583 are low-voltage, ♦ Pin Compatible with Industry-Standard CMOS a ..
MAX4581CEE ,Low-Voltage, CMOS Analog Multiplexers/SwitchesMAX4581/MAX4582/MAX458319-1328; Rev 1; 10/99Low-Voltage, CMOS AnalogMultiplexers/Switches__________ ..
MAX4581CEE ,Low-Voltage, CMOS Analog Multiplexers/SwitchesGeneral Description ________
MAX1744AUB+-MAX1744EUB+-MAX1745AUB+-MAX1745EUB+-MAX1745EUB+T-MAX1745EUB-T
High-Voltage, Step-Down DC-DC Controller in µMAX
General DescriptionThe MAX1744/MAX1745 are step-down DC-DC con-
trollers capable of handling up to 36V inputs. These
parts use a proprietary current-limited control scheme
for excellent light- and full-load efficiency, while their
330kHz (max) switching frequency permits small exter-
nal components for space-critical applications.
Operation to 100% duty cycle permits the lowest possi-
ble dropout voltage.
The MAX1744 contains an internal feedback network
that provides a pin-selectable output voltage of either
3.3V or 5V. The MAX1745 uses an external feedback
network to generate an adjustable output voltage
between 1.25V and 18V.
The MAX1744/MAX1745 are available in a space-sav-
ing 10-pin μMAX®package.
________________________ApplicationsAutomotive Electronics
Telecom Systems
Wall-Cube-Powered Devices
Industrial Control Systems
Firewire®/IEEE®1394
____________________________FeaturesHigh-Voltage Operation (Up to 36V IN)Efficiency > 90%Output Power Capability Exceeds 50W10-Pin µMax PackageLow-Dropout Voltage100% (max) Duty Cycle90µA Quiescent Current4µA Shutdown CurrentUp to 330kHz Switching FrequencyOutput Voltage
5V or 3.3V (MAX1744)
Adjustable 1.25V to 18V (MAX1745)Current-Limited Control Scheme
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX19-1776; Rev 4; 8/09
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1744EUB+ -40°C to +85°C 10 μMAX MAX1744AUB+ -40°C to +125°C 10 μMAX
MAX1744EUB/V+ -40°C to +85°C 10 μMAX
MAX1745EUB+ -40°C to +85°C 10 μMAX MAX1745AUB+ -40°C to +125°C 10 μMAX
MAX1745EUB/V+ -40°C to +85°C 10 μMAX
GNDOUT
REF
MAX1744
3/5
3.3V
OFFSHDNVHEXTP
4.5V TO 36V
OUT
3.3V
OR 5V
Typical Operating CircuitEXT
3/5 (FB)
( ) ARE FOR MAX1745 ONLY.
REF
GND
MAX1744
MAX1745
μMAX
TOP VIEWOUT
SHDN
Pin Configuration
EVALUATION KIT
AVAILABLEμMAX is a registered trademark of Maxim Integrated Products, Inc.
Firewire is a registered trademark of Apple, Inc.
IEEE is a registered service mark of the Institute of Electrical
and Electronics Engineers, Inc.+Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes an automotive qualified part.
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= VSHDN= 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA
= 0°C to +85°C, unless otherwise noted. Typical values at VIN= VSHDN=
36V, 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.
IN, EXT, SHDNto GND...........................................-0.3V to +38V
VH to GND..............................................................-0.3V to +34V
VH, EXT to IN............................................................-7V to +0.3V
CS, OUT to GND....................................................-0.3V to +20V
FB, 3/5, REF to GND.....................................-0.3V to (VL + 0.3V)
VL to GND...................................................................-0.3V to 6V
Continuous Power Dissipation (TA= +70°C)
10-Pin μMAX (derate 5.6mW/°C above 70°C).............444mW
Operating Temperature Range
MAX174_EUB..................................................-40°C to +85°C
MAX174_AUB................................................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................+300°C
PARAMETERCONDITIONSMINTYPMAXUNITSInput Voltage Range4.536V
Supply Current into INVSHDN = VIN = 5.5V to 36V90140μA
Shutdown Supply CurrentSHDN = GND412μA
3/5 = VL4.855.005.15Output Voltage (MAX1744)3/5 = GND3.203.303.40V
OUT Input Current (MAX1744)3/5 = VL, VOUT = 5V2844μA
FB Threshold Voltage (MAX1745)Falling edge, hysteresis = 8mV1.221.251.28V
FB Input Current (MAX1745)-5050nA
VH Output Voltage with Respect to INVIN = 5.5V to 36V, IVH = 100μA to 20mA-6.0-5.3-4.3V
VL Output VoltageVIN = 5.5V to 36V, IVL = 100μA to 2mA4.55.05.5V
VL Undervoltage Lockout2.03.04.1V
VCS = VOUT = 2.5V to 18V85100115CS Threshold VoltageVCS = VOUT = VGND80110150mV
VCS = VOUT = 2.5V to 18V01525CS Input CurrentVCS = VOUT = VGND-250μA
SHDN, 3/5 Logic-High ThresholdVIN = 4.5V to 36V2.4V
SHDN, 3/5 Logic-Low ThresholdVIN = 4.5V to 36V0.4V
3/5 Input CurrentSHDN = GND±1μA
3/5 = GND±1SHDN Input CurrentVSHDN = 36V12μA
EXT Resistance820Ω
Minimum EXT Off-Time1.52.02.5μs
Minimum EXT On-Time0.71.01.5μs
Output Line RegulationFigure 1, 5.5V < VIN < 36V, ILOAD = 1A5mV/V
Output Load RegulationFigure 1, VIN = 12V, 30mA < ILOAD < 2A15mV/A
Reference VoltageIREF = 01.221.251.28V
REF Load Regulation0 ≤ IREF ≤ 100μA410mV
REF Line RegulationVIN = 4.5V to 36V, IREF = 03060μV/V
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
ELECTRICAL CHARACTERISTICS(VIN= VSHDN= 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA
= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETERCONDITIONSMINMAXUNITSInput Voltage Range4.536V
Supply Current into INVSHDN = VIN = 5.5V to 36V140μA
Shutdown Supply CurrentSHDN = GND12μA
3/5 = VL4.855.15Output Voltage (MAX1744)3/5 = GND3.203.40V
OUT Input Current (MAX1744)3/5 = VL, VOUT = 5V44μA
FB Threshold Voltage (MAX1745)Falling edge, hysteresis = 8mV1.221.28V
FB Input Current (MAX1745)-5050nA
VH Output Voltage with Respect to INVIN = 5.5V to 36V, IVH = 100μA to 20mA-6.0V-4.3VV
VL Output VoltageVIN = 5.5V to 36V, IVL = 100μA to 2mA4.55.5V
VL Undervoltage Lockout2.04.1V
VCS = VOUT = 2.5V to 18V85115CS Threshold VoltageVCS = VOUT = VGND80150mV
VCS = VOUT = 2.5V to 18V025CS Input CurrentVCS = VOUT = VGND-250μA
SHDN, 3/5 Logic-High ThresholdVIN = 4.5V to 36V2.4V
SHDN, 3/5 Logic-Low ThresholdVIN = 4.5V to 36V0.4V
3/5 Input CurrentSHDN = GND±1μA
3/5 = GND±1SHDN Input CurrentVSHDN = 36V12μA
EXT Resistance20Ω
Minimum EXT Off-Time1.52.5μs
Minimum EXT On-Time0.71.5μs
Reference VoltageIREF = 01.221.28V
REF Load Regulation0 ≤ IREF ≤ 100μA10mV
REF Line RegulationVIN = 4.5V to 36V, IREF = 060μV/V
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
ELECTRICAL CHARACTERISTICS(VIN= VSHDN= 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA
= -40°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETERCONDITIONSMINMAXUNITSInput Voltage Range4.536V
Supply Current into INVSHDN = VIN = 5.5V to 36V140μA
Shutdown Supply CurrentSHDN = GND15μA
3/5 = VL4.855.15Output Voltage (MAX1744)3/5 = GND3.203.40V
OUT Input Current (MAX1744)3/5 = VL, VOUT = 5V44μA
FB Threshold Voltage (MAX1745)Falling edge, hysteresis = 8mV1.221.28V
FB Input Current (MAX1745)-5050nA
VH Output Voltage with Respect to INVIN = 5.5V to 36V, IVH = 100μA to 20mA-6.0V-4.3VV
VL Output VoltageVIN = 5.5V to 36V, IVL = 100μA to 2mA4.55.5V
VL Undervoltage Lockout1.64.1V
VCS = VOUT = 2.5V to 18V85115CS Threshold VoltageVCS = VOUT = VGND80150mV
VCS = VOUT = 2.5V to 18V025CS Input CurrentVCS = VOUT = VGND-250μA
SHDN, 3/5 Logic-High ThresholdVIN = 4.5V to 36V2.4V
SHDN, 3/5 Logic-Low ThresholdVIN = 4.5V to 36V0.4V
3/5 Input CurrentSHDN = GND±1μA
3/5 = GND±1SHDN Input CurrentVSHDN = 36V12μA
EXT Resistance20Ω
Minimum EXT Off-Time1.52.5μs
Minimum EXT On-Time0.71.5μs
Reference VoltageIREF = 01.221.28V
REF Load Regulation0 ≤ IREF ≤ 100μA10mV
REF Line RegulationVIN = 4.5V to 36V, IREF = 080μV/V
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAXEFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)
MAX1744/5toc01
LOAD CURRENT (A)
EFFICIENCY (%)40
A: VIN = +5.5V
B: VIN = +12.0V
C: VIN = +24.0V
D: VIN = +36.0VD
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5.0V)
MAX1744/5toc02
LOAD CURRENT (A)
EFFICIENCY
(%)
A: VIN = +7.2V
B: VIN = +12.0V
C: VIN = +24.0V
D: VIN = +36.0VC
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (5.5V TO 36V)
MAX1744/5toc03
INPUT VOLTAGE (V)
QUIESCENT CURRENT (
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (3.5V TO 5.5V)
MAX1744/5toc04
INPUT VOLTAGE (V)
QUIESCENT CURRENT (mA)
VOUT = 3.3V
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX1744/5toc05
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)
VOUT = 3.3V
IOUT = 2.0A
IN PIN QUIESCENT CURRENT
vs. TEMPERATUREMAX1744/5toc06
TEMPERATURE (°C)
QUIESCENT CURRENT (
EXT RISE AND FALL TIMES
vs. CAPACITANCE
MAX1744/5toc07
tRISE
AND t
FALL
(ns)
VIN = +5V
tFALL
tRISE
EXT RISE AND FALL TIMES
vs. TEMPERATUREMAX1744/5toc08
RISE
AND t
FALL
(ns)
tRISE
tFALL
VIN = +5V
CL = 1000pF
CURRENT-SENSE TRIP LEVEL
vs. TEMPERATUREMAX1744/5toc09
CURRENT-SENSE TRIP LEVEL (mV)
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25°C, unless otherwise specified.)
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
Typical Operating Characteristics (continued)(Circuit of Figure 1, TA = +25°C, unless otherwise specified.)
REFERENCE OUTPUT VOLTAGE CHANGE
vs. TEMPERATUREMAX1744/5toc10
TEMPERATURE (°C)
REFERENCE OUTPUT VOLTAGE CHANGE (%)
VOUT
2V/div
SHUTDOWN
PULSE
5V/div
MAX1744
ENTERING/EXITING SHUTDOWNMAX1744/5toc11
2ms/div
RL = 3.3Ω
VIN = 7.2V, VOUT = 3.3V, LOAD CURRENT = 0.1A TO 2A
A: VOUT, 50mV/div, 3.3V AC-COUPLED
B: LOAD CURRENT, 1A/div
LOAD-TRANSIENT RESPONSEMAX1744/5toc12A
50μs/div
VOUT = 5V, LOAD CURRENT = 1A
A: VOUT, 100mV/div, AC-COUPLED
B: VIN, 6V TO 12V, 5V/div
LINE-TRANSIENT RESPONSEMAX1744/5toc13A
4ms/div
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
Detailed DescriptionThe MAX1744/MAX1745 are high-voltage step-down
DC-DC converter controllers. These devices offer high
efficiency over a wide range of input/output voltages
and currents, making them optimal for use in applica-
tions such as telecom, automotive, and industrial con-
trol. Using an external P-channel MOSFET and
current-sense resistor allows design flexibility and
improved efficiency. The MAX1744/MAX1745 automati-
cally switch from PWM operation at medium and heavy
loads to pulse-skipping operation at light loads to
improve light-load efficiency. The low 90μA quiescent
current further optimizes these parts for applications
where low input current is critical. Operation to 100%
duty cycle allows the lowest possible dropout voltage,
which allows a wider input voltage variation. The small
size, high switching frequency, and low parts count
minimize the required circuit board area and compo-
nent cost. Figure 1 shows the MAX1744 typical applica-
Operating ModesWhen delivering low output currents, the MAX1744/
MAX1745 operate in discontinuous-conduction mode.
Current through the inductor starts at zero, rises as
high as the current limit, then ramps down to zero dur-
ing each cycle (Figure 3). The switch waveform exhibits
ringing, which occurs at the resonant frequency of the
inductor and stray capacitance, due to residual energy
trapped in the core when the commutation diode (D1 in
Figure 1) turns off.
When delivering medium-to-high output currents, the
MAX1744/MAX1745 operate in PWM continuous-con-
duction mode (Figure 4). In this mode, current always
flows through the inductor and never ramps to zero.
The control circuit adjusts the switch duty cycle to
maintain regulation without exceeding the peak switch-
ing current set by the current-sense resistor.
Pin Description
NAME
PIN
MAX1744MAX1745
FUNCTIONGNDGNDGround
2VLVL5V Linear Regulator Output. VL provides power to the internal circuitry and can supply up
to 1mA to an external load. Bypass VL to GND with 4.7μF or greater capacitor.REFREF1.25V Reference Output. REF can supply up to 100μA to an external load. Bypass REF to
GND with a 0.1μF or greater ceramic capacitor.3/5—3.3V or 5V Selection. Connect 3/5 to GND to set the output voltage to 3.3V. Connect 3/5 to
VL to set the output voltage to 5V.FB
Feedback Input for Adjustable Output Operation. Connect to an external voltage-divider
between the output and FB to set the output voltage. The regulation voltage threshold is
1.25V.OUTOUT
Sense Input for Fixed 5V or 3.3V Output Operation (MAX1744) and Negative Current-Sense
Input (MAX1744/5). OUT is connected to an internal voltage-divider (MAX1744). OUT does
not supply current.
6CSCS
Current-Sense Input. Connect the current-sense resistor between CS and OUT. External
MOSFET is turned off when the voltage across the resistor is equal to or greater than the
current limit trip level (100mV).SHDNSHDN
Active-Low Shutdown Input. Connect SHDN to IN for normal operation. Drive SHDN to low
to shut the part off. In shutdown mode, the reference, output, external MOSFET, and
internal regulators are turned off.
8VHVH
High-Side Linear Regulator Output. VH provides a regulated output voltage that is 5V below
IN. The external P-channel MOSFET gate is driven between IN and VH. Bypass VH to IN
with a 4.7μF or greater capacitor (see the Capacitor Selection section).EXTEXTGate Drive for External P-Channel MOSFET. EXT swings between IN and VH.ININPositive Supply Input. Bypass IN to GND with a 0.47μF or greater ceramic capacitor.
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controllers in µMAX
100% Duty Cycle and DropoutThe MAX1744/MAX1745 operate with a duty cycle up to
100%. This feature extends the input voltage range 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 output
voltages when the input is low enough for the output 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:
Regulation Control SchemeThe MAX1744/MAX1755 have a unique operating
scheme that allows PWM operation at medium and high
current, with automatic switching to pulse-skipping
mode at lower currents to improve light-load efficiency.
Figure 2 shows the simplified block diagram.
Under medium- and heavy-load operation, the inductor
current is continuous and the part operates in PWM
mode. In this mode, the switching frequency is set by
either the 1μs minimum on-time or the 2μs minimum off-
time, depending on the duty cycle. The duty cycle is
approximately the output voltage divided by the input
voltage. If the duty cycle is less than 33%, the minimum
on-time controls the frequency; and the frequency is
approximately f ≈1MHz ✕D, where D is the duty cycle.
If the duty cycle is greater than 33%, the off-time sets the
frequency; and the frequency is approximately f ≈500kHz(1 - D).
In both cases, the voltage is regulated by the error
comparator. For low duty cycles (<33%), the MOSFET
is turned on for the minimum on-time, causing fixed-on-
time operation. During the MOSFET on-time, the output
voltage rises. Once the MOSFET is turned off, the volt-
age drops to the regulation threshold (set by the inter-
nal voltage-divider for the MAX1745 and by the external
voltage-divider for the MAX1744), at which time another
cycle is initiated. For high duty cycles (>33%), the
MOSFET remains off for the minimum off-time, causing
fixed-off-time operation. In this case, the MOSFET
remains on until the output voltage rises to the regula-
tion threshold. Then the MOSFET turns off for the mini-
mum off-time, initiating another cycle.
By switching between fixed-on-time and fixed-off-time
operation, the MAX1744/MAX1745 can operate at high
input-output ratios, yet still operate up to 100% duty
cycle for low dropout. Note that when transitioning from
fixed-on-time to fixed-off-time operation, the output volt-
age drops slightly due to the output ripple voltage. In
fixed-on-time operation, the minimum output voltage is
regulated, but in fixed-off-time operation, the maximum
output voltage is regulated. Thus, as the input voltage
drops below approximately three times the output volt-
age, a decrease in line regulation can be expected.
The drop in voltage is approximately VDROP≈VRIPPLE/ 2.
At light output loads, the inductor current is discontinu-
ous, causing the MAX1744/MAX1745 to operate at
Figure 1. Typical Application Circuit
GND
REF
MAX1744
3/5
3.3V
OFFSHDN
EXT
INPUT
4.5V TO 36V
NIHON
EC2IQ506
FAIRCHILD
NDS9407
OUT
OUT
3.3V OR 5V
220μF
22μH
RSENSE
40mΩ
4.7μFC2
4.7μF
LOW ESR
0.47μF
Dropoutvoltage=R+ROUTDS(ON)SENNSEINDUCTOR+R⎡⎣⎤⎦
