MAX1954EUB ,Low-Cost / High-Frequency / Current-Mode PWM Buck ControllerELECTRICAL CHARACTERISTICS(V = 5V, V - V = 5V, T = -40°C to +85°C, unless otherwise noted. Typical ..
MAX1954EUB ,Low-Cost / High-Frequency / Current-Mode PWM Buck ControllerELECTRICAL CHARACTERISTICS (continued)(V = 5V, V - V = 5V, T = -40°C to +85°C, unless otherwise not ..
MAX1954EUB ,Low-Cost / High-Frequency / Current-Mode PWM Buck ControllerELECTRICAL CHARACTERISTICS (continued)(V = 5V, V - V = 5V, T = -40°C to +85°C, unless otherwise not ..
MAX1954EUB+ ,Low-Cost, High-Frequency, Current-Mode PWM Buck ControllersApplicationsPrinters and ScannersILIM 1 10 BSTGraphic Cards and Video CardsCOMP 2 9 LXPCs and Serve ..
MAX1954EUB+ ,Low-Cost, High-Frequency, Current-Mode PWM Buck ControllersApplicationsPrinters and ScannersILIM 1 10 BSTGraphic Cards and Video CardsCOMP 2 9 LXPCs and Serve ..
MAX1954EUB+T ,Low-Cost, High-Frequency, Current-Mode PWM Buck ControllersELECTRICAL CHARACTERISTICS (continued)(V = 5V, V - V = 5V, T = -40°C to +85°C, unless otherwise not ..
MAX491 ,Low-Power, Slew-Rate-Limited RS-485/RS-422 TransceiversApplicationsIndustrial-Control Local Area Networks Ordering Information appears at end of data shee ..
MAX491CPD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversGeneral Description ________
MAX491CPD+ ,Low-Power, Slew-Rate-Limited RS-485/RS-422 TransceiversApplicationsMAX3483E/MAX3485E/MAX3486E/MAX3488E/Low-Power RS-485 TransceiversMAX3490E/MAX3491E: +3. ..
MAX491CSD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversApplications ______________Ordering InformationLow-Power RS-485 TransceiversPART TEMP. RANGE PIN-PA ..
MAX491CSD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversMAX481/MAX483/MAX485/MAX487–MAX491/MAX148719-0122; Rev 5; 2/96Low-Power, Slew-Rate-LimitedRS-485/RS ..
MAX491CSD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversELECTRICAL CHARACTERISTICS(V = 5V ±5%, T = T to T , unless otherwise noted.) (Notes 1, 2)CC A MIN M ..
MAX1953EUB-MAX1954EUB-MAX1957EUB
Low-Cost / High-Frequency / Current-Mode PWM Buck Controller
General DescriptionThe MAX1953/MAX1954/MAX1957 is a family of versa-
tile, economical, synchronous current-mode, pulse-width
modulation (PWM) buck controllers. These step-down
controllers are targeted for applications where cost and
size are critical.
The MAX1953 operates at a fixed 1MHz switching fre-
quency, thus significantly reducing external component
size and cost. Additionally, excellent transient response
is obtained using less output capacitance. The MAX1953
operates from low 3V to 5.5V input voltage and can sup-
ply up to 10A of output current. Selectable current limit is
provided to tailor to the external MOSFETs’ on-resistance
for optimum cost and performance. The output voltage is
adjustable from 0.8V to 0.86VIN.
With the MAX1954, the drain-voltage range on the high-
side FET is 3V to 13.2V and is independent of the supply
voltage. It operates at a fixed 300kHz switching frequen-
cy and can be used to provide up to 25A of output cur-
rent with high efficiency. The output voltage is adjustable
from 0.8V to 0.86VHSD.
The MAX1957 features a tracking output voltage range of
0.4V to 0.86VINand is capable of sourcing or sinking
current for applications such as DDR bus termination
and PowerPC™/ASIC/DSP core supplies. The MAX1957
operates from a 3V to 5.5V input voltage and at a fixed
300kHz switching frequency.
The MAX1953/MAX1954/MAX1957 provide a COMP pin
that can be pulled low to shut down the converter in
addition to providing compensation to the error amplifier.
An input undervoltage lockout (ULVO) is provided to
ensure proper operation under power-sag conditions to
prevent the external power MOSFETs from overheating.
Internal digital soft-start is included to reduce inrush cur-
rent. The MAX1953/MAX1954/MAX1957 are available in
tiny 10-pin µMAX packages.
ApplicationsPrinters and Scanners
Graphic Cards and Video Cards
PCs and Servers
Microprocessor Core Supply
Low-Voltage Distributed Power
Telecommunications and Networking
FeaturesLow-Cost Current-Mode ControllersFixed-Frequency PWMMAX1953
1MHz Switching Frequency
Small Component Size, Low Cost
Adjustable Current LimitMAX1954
3V to 13.2V Input Voltage
25A Output Current Capability
93% Efficiency
300kHz Switching FrequencyMAX1957
Tracking 0.4V to 0.86VINOutput Voltage Range
Sinking and Sourcing Capability of 3AShutdown FeatureAll N-Channel MOSFET Design for Low CostNo Current-Sense Resistor NeededInternal Digital†
Soft-StartThermal Overload ProtectionSmall 10-Pin µMAX Package
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
Ordering Information19-2373; Rev 0; 4/02
Pin Configurations†Patent Pending
PowerPC is a trademark of Motorola, Inc.
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
ABSOLUTE MAXIMUM RATINGSStresses 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, FB to GND...........................................................-0.3V to +6V
LX to BST..................................................................-6V to +0.3V
BST to GND............................................................-0.3V to +20V
DH to LX....................................................-0.3V to (VBST+ 0.3V)
DL, COMP to GND.......................................-0.3V to (VIN+ 0.3V)
HSD, ILIM, REFIN to GND........................................-0.3V to 14V
PGND to GND.......................................................-0.3V to +0.3V
IDH, IDL................................................................±100mA (RMS)
Continuous Power Dissipation (TA= +70°C)
(derate 5.6mW/°C above +70°C)..................................444mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
ELECTRICAL CHARACTERISTICS (continued)(VIN= 5V, VBST- VLX= 5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)(Note 1)
Note 2:HSD and IN are externally connected for applications where VHSD< 5.5V.
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controllerypical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
Pin Description
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
Detailed DescriptionThe MAX1953/MAX1954/MAX1957 are single-output,
fixed-frequency, current-mode, step-down, PWM, DC-
DC converter controllers. The MAX1953 switches at
1MHz, allowing the use of small external components for
small applications. Table 1 lists suggested components.
The MAX1954 switches at 300kHz for higher efficiency
and operates from a wider range of input voltages.
Figure 1 is the MAX1953 typical application circuit. The
MAX1953/MAX1954/MAX1957 are designed to drive a
pair of external N-channel power MOSFETs in a syn-
chronous buck topology to improve efficiency and cost
compared with a P-channel power MOSFET topology.
The on-resistance of the low-side MOSFET is used for
short-circuit current-limit sensing, while the high-side
MOSFET on-resistance is used for current-mode feed-
back and current-limit sensing, thus eliminating the
need for current-sense resistors. The MAX1953 has
three selectable short-circuit current-limit thresholds:
105mV, 210mV, and 320mV. The MAX1954 and
MAX1957 have 210mV fixed short-circuit current-limit
thresholds. The MAX1953/MAX1954/MAX1957 accept
input voltages from 3V to 5.5V. The MAX1954 is config-
ured with a high-side drain input (HSD) allowing an
extended input voltage range of 3V to 13.2V that is
independent of the input supply (Figure 2). The
MAX1957 is tailored for tracking output voltage applica-
tions such as DDR bus termination supplies, referred to
as VTT. It utilizes a resistor-divider network connected
to REFIN to keep the 1/2 ratio tracking between VTT
and VDDQ(Figure 3). The MAX1957 can source and
sink up to 3A. Figure 4 shows the MAX1954 20A circuit.
DC-DC Converter Control ArchitectureThe MAX1953/MAX1954/MAX1957 step-down convert-
ers use a PWM, current-mode control scheme. An inter-
nal transconductance amplifier establishes an integrated
error voltage. The heart of the PWM controller is an open-
loop comparator that compares the integrated voltage-
feedback signal against the amplified current-sense
signal plus the slope compensation ramp, which are
summed into the main PWM comparator to preserve
inner-loop stability and eliminate inductor staircasing. At
each rising edge of the internal clock, the high-side
MOSFET turns on until the PWM comparator trips or the
maximum duty cycle is reached. During this on-time, cur-
rent ramps up through the inductor, storing energy in a
magnetic field and sourcing current to the output. The
current-mode feedback system regulates the peak
inductor current as a function of the output voltage error
signal. The circuit acts as a switch-mode transconduc-
tance amplifier and pushes the output LC filter pole nor-
mally found in a voltage-mode PWM to a higher
frequency.
During the second half of the cycle, the high-side MOS-
FET turns off and the low-side MOSFET turns on. The
inductor releases the stored energy as the current ramps
down, providing current to the output. The output capaci-
tor stores charge when the inductor current exceeds the
required load current and discharges when the inductor
current is lower, smoothing the voltage across the load.
Under overload conditions, when the inductor current
exceeds the selected current-limit (see the Current Limit
Circuitsection), the high-side MOSFET is not turned on
at the rising clock edge and the low-side MOSFET
remains on to let the inductor current ramp down.
The MAX1953/MAX1954/MAX1957 operate in a forced-
PWM mode. As a result, the controller maintains a con-
stant switching frequency, regardless of load, to allow for
easier postfiltering of the switching noise.
MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
