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The MAX1533/MAX1537 are dual step-down, switch-mode
power-supply (SMPS) controllers with synchronous
rectification, intended for main 5V/3.3V power
generation in battery-powered systems. Fixed-frequency
operation with optimal interleaving minimizes input
ripple current from the lowest input voltages up to the
26V maximum input. Optimal 40/60 interleaving allows
the input voltage to go down to 8.3V before duty-cycle
overlap occurs, compared to 180° out-of-phase regulators
where the duty-cycle overlap occurs when the
input drops below 10V. Output current sensing provides
accurate current limit using a sense resistor.
Alternatively, power dissipation can be reduced using
lossless inductor current sensing.
Internal 5V and 3.3V linear regulators power the
MAX1533/MAX1537 and their gate drivers, as well as
external keep-alive loads, up to a total of 100mA. When
the main PWM regulators are in regulation, automatic
bootstrap switches bypass the internal linear regulators,
providing currents up to 200mA from each linear output.
An additional 5V to 23V adjustable internal 150mA linear
regulator is typically used with a secondary winding to
provide a 12V supply.
The MAX1533/MAX1537 include on-board power-up
sequencing, a power-good (PGOOD) output, digital
soft-start, and internal soft-shutdown output discharge
that prevents negative voltages on shutdown. The
MAX1533 is available in a 32-pin 5mm x 5mm thin QFN
package, and the MAX1537 is available in a 36-pin
6mm x 6mm thin QFN package. The exposed backside
pad improves thermal characteristics for demanding
linear keep-alive applications.
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