MAX15053_1107 Datasheet, PDF (11/21 Pages) Maxim Integrated Products – High-Efficiency, 2A, Current-Mode Synchronous, Step-Down Switching Regulator

High-Efficiency, 2A, Current-Mode
Synchronous, Step-Down Switching Regulator
Detailed Description
The MAX15053 high-efficiency, current-mode switching
regulator can deliver up to 2A of output current. The
MAX15053 provides output voltages from 0.6V to 0.94 x
VIN from 2.7V to 5.5V input supplies, making the device
ideal for on-board point-of-load applications.
The MAX15053 delivers current-mode control architec-
ture using a high gain transconductance error amplifier.
The current-mode control architecture facilitates easy
compensation design and ensures cycle-by-cycle cur-
rent limit with fast response to line and load transients.
The MAX15053 features a 1MHz fixed switching frequen-
cy, allowing for all-ceramic capacitor designs and fast
transient responses. The high operating frequency mini-
mizes the size of external components. The MAX15053
is available in a 1.5mm x 1.5mm (3 x 3 array) x 0.5mm
pitch WLP package.
The MAX15053 offers a selectable skip-mode functional-
ity to reduce current consumption and achieve a higher
efficiency at light output loads. The low RDS(ON) integrat-
ed switches (30mI high-side and 18mI low-side, typ)
ensure high efficiency at heavy loads while minimizing
critical inductances, making the layout design a much
simpler task with respect to discrete solutions. Utilizing
a simple layout and footprint assures first-pass success
in new designs.
The MAX15053 features 1MHz Q15%, factory-trimmed,
fixed-frequency PWM mode operation. The MAX15053 also
offers capacitor-programmable, soft-start reducing inrush
current, startup into PREBIAS operation, and a PGOOD
open-drain output for sequencing with other devices.
Controller Function–PWM Logic
The controller logic block is the central processor that
determines the duty cycle of the high-side MOSFET
under different line, load, and temperature conditions.
Under normal operation, where the current-limit and
temperature protection are not triggered, the controller
logic block takes the output from the PWM comparator
and generates the driver signals for both high-side and
low-side MOSFETs. The control logic block controls the
break-before-make logic and all the necessary timing.
The high-side MOSFET turns on at the beginning of
the oscillator cycle and turns off when the COMP volt-
age crosses the internal current-mode ramp waveform,
which is the sum of the slope compensation ramp and
the current-mode ramp derived from inductor current
(current-sense block). The high-side MOSFET also turns
off if the maximum duty cycle is 94%, or when the current
limit is reached. The low-side MOSFET turns on for the
remainder of the oscillation cycle.
Starting into a Prebiased Output
The MAX15053 can soft-start into a prebiased output
without discharging the output capacitor. In safe pre-
biased startup, both low-side and high-side MOSFETs
remain off to avoid discharging the prebiased output.
PWM operation starts when the voltage on SS/REFIN
crosses the voltage on FB.
The MAX15053 can start into a prebiased voltage higher
than the nominal set point without abruptly discharg-
ing the output. Forced PWM operation starts when the
SS/REFIN voltage reaches 0.58V (typ), forcing the
converter to start. In case of prebiased output, below
or above the output nominal set point, if low-side sink
current-limit threshold (set to the reduced value of -0.4A
(typ) for the first 32 clock cycles and then set to -4A typ)
is reached, the low-side switch turns off before the end of
the clock period, and the high-side switch turns on until
one of the following conditions is satisfied:
• High-side source current hits the reduced high-side
current limit (0.4A, typ); in this case, the high-side
switch is turned off for the remaining time of the clock
period.
• The clock period ends. Reduced high-side current
limit is activated to recirculate the current into the
high-side power switch rather than into the internal
high-side body diode, which could be damaged.
Low-side sink current limit is provided to protect the
low-side switch from excessive reverse current dur-
ing prebiased operation.
In skip mode operation, the prebias output needs to be
lower than the set point.
Enable Input
The MAX15053 features independent device enable
control and power-good signal that allow for flexible
power sequencing. Drive the enable input (EN) high to
enable the regulator, or connect EN to IN for always-on
operation. Power-good (PGOOD) is an open-drain out-
put that asserts when VFB is above 555mV (typ), and
deasserts low if VFB is below 527mV (typ).
Programmable Soft-Start (SS/REFIN)
The MAX15053 utilizes a soft-start feature to slowly
ramp up the regulated output voltage to reduce input
inrush current during startup. Connect a capacitor from
SS/REFIN to GND to set the startup time (see the Setting
the Soft-Start Time section for capacitor selection details).
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