MAX1954AEUB ,3.0 V to 13.2 V, low-cost, current-mode PWM buck controller with foldback current limitELECTRICAL CHARACTERISTICS(V = 5V, V - V = 5V, T = 0°C to +85°C, unless otherwise noted.)IN BST LX ..
MAX1954AEUB ,3.0 V to 13.2 V, low-cost, current-mode PWM buck controller with foldback current limitApplications Ordering InformationPrinters and Scanners PART TEMP RANGE PIN-PACKAGE Graphic Cards an ..
MAX1954AEUB+ ,Low-Cost, Current-Mode PWM Buck Controller with Foldback Current LimitApplicationsOrdering InformationPrinters and Scanners PART TEMP RANGE PIN-PACKAGEGraphic Cards and ..
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 ..
MAX490ESA+T ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplications:state. The receiver input has a fail-safe feature that guar-MAX3440E–MAX3444E: ±15kV E ..
MAX490MJA ,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 ..
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 ..
MAX1954AEUB
3.0 V to 13.2 V, low-cost, current-mode PWM buck controller with foldback current limit
General DescriptionThe MAX1954A synchronous current-mode, pulse-
width modulation (PWM) buck controller is pin compati-
ble with the popular MAX1954 and is suitable for
applications where cost and size are critical.
The MAX1954A operates from an input voltage range of
3.0V to 13.2V, independent of the IC supply. The output
voltage is adjustable down to 0.8V. The IC operates at
a fixed 300kHz switching frequency and provides up to
25A of output current with efficiency up to 95%. This
controller has excellent transient response resulting in
smaller output capacitance.
The MAX1954A features foldback current limiting that
greatly reduces input current and component power
dissipation during output overload or short-circuit
conditions.
The compensation and shutdown control (COMP) input,
in addition to providing compensation to the error
amplifier, can be pulled low to shut down the converter.
An input undervoltage lockout is provided to ensure
proper operation during power sags to prevent the
external power MOSFETs from overheating. Internal
digital soft-start is included to reduce inrush current
and save an external capacitor.
The MAX1954A is available in a tiny 10-pin µMAX pack-
age to minimize PC board space.
ApplicationsPrinters and Scanners
Graphic Cards and Video Cards
PCs and Servers
Microprocessor Cores
Low-Voltage Distributed Power
Telecom/Networks
FeaturesCurrent-Mode ControllerFixed-Frequency PWMFoldback Current LimitOutput Down to 0.8V with ±1% FB Accuracy3.0V to 13.2V Input Voltage300kHz Switching Frequency25A Output-Current Capability93% EfficiencyAll-N-Channel-MOSFET Design for Low CostNo Current-Sense Resistor NeededInternal Digital Soft-StartSmall 10-Pin µMAX Package
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
Ordering Information
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
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 to GND..............................................................-0.3V to 14V
PGND to GND.......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (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
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
ELECTRICAL CHARACTERISTICS (continued)(VIN = 5V, VBST - VLX = 5V, TA
= 0°C to +85°C,unless otherwise noted.)
ELECTRICAL CHARACTERISTICS
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
Note 2:Specifications to -40°C are guaranteed by design and not production tested.
ELECTRICAL CHARACTERISTICS (continued)(VIN = 5V, VBST - VLX = 5V, TA
= -40°C to +85°C,unless otherwise noted.) (Note 2)
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limitypical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
Detailed DescriptionThe MAX1954A single-output, current-mode, PWM, step-
down DC-DC controller features foldback current limit
and switches at 300kHz for high efficiency. The
MAX1954A is designed to drive a pair of external N-
channel power MOSFETs in a synchronous buck topolo-
gy 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’s on-resis-
tance is used for current-mode feedback, thus
eliminating the need for current-sense resistors. The
short-circuit current limit is fixed at 135mV. The foldback
current scheme reduces the input current during short-
circuit and severe-overload conditions. The MAX1954A
is configured with a high-side drain input (HSD) allowing
an extended input voltage range of 3V to 13.2V that is
independent of the IC input supply (Figure 1).
DC-DC Converter Control ArchitectureThe MAX1954A step-down converter uses a PWM, cur-
rent-mode control scheme. An internal transconductance
amplifier establishes an integrated error voltage. An
open-loop comparator compares the integrated voltage-
feedback signal against the amplified current-sense sig-
nal plus the slope compensation ramp, which is summed
into the main PWM comparator to preserve inner-loop sta-
bility 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, current 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 transconductance amplifier because
the average inductor current is close to the peak inductor
current (assuming the inductor is large enough to provide
a reasonably small ripple current). This pushes the output
inductance-capacitance filter pole normally found in a
voltage-mode PWM to a higher frequency.
Pin Description
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current LimitDuring the second half of the cycle, the high-side
MOSFET 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 current limit (see the Current-LimitCircuit
section), the high-side MOSFET is not turned on at the ris-
ing clock edge and the low-side MOSFET remains on to
let the inductor current ramp down.
The MAX1954A operates in a forced-PWM mode; there-
fore, the controller maintains a constant switching fre-
quency, regardless of load, to allow for easier post-
filtering of the switching noise.
Current-Sense AmplifierThe current-sense circuit amplifies the current-sense
voltage (the high-side MOSFET’s on-resistance
(RDS(ON)) multiplied by the inductor current). This ampli-
fied current-sense signal and the internal slope-compen-
sation signal are summed (VSUM) together and fed into
the PWM comparator’s inverting input. The PWM com-
parator shuts off the high-side MOSFET when VSUM
exceeds the integrated feedback voltage (VCOMP).
MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current LimitPlace the high-side MOSFET as close as possible to
the controller and connect HSD and LX to the MOSFET
using Kelvin-sense connections to guarantee current-
sense accuracy and improve stability.
Current-Limit CircuitThe current-limit circuit employs a lossless, foldback,
valley current-limiting algorithm that uses the low-side
MOSFET’s on-resistance as the sensing element. Once
the high-side MOSFET turns off, the voltage across the
low-side MOSFET is monitored. If the voltage across the
low-side MOSFET (RDS(ON)x IINDUCTOR) does not
exceed the current limit, the high-side MOSFET turns on
normally. In this condition, the output drops smoothly out
of regulation. If the voltage across the low-side MOSFET
exceeds the current-limit threshold at the beginning of a
new oscillator cycle, the low-side MOSFET remains on
and the high-side MOSFET remains off.
