Datasheet

11Maxim Integrated
High-Efficiency, 4A, Step-Down DC-DC
Regulators with Internal Power Switches
MAX15066/MAX15166
Detailed Description
The MAX15066/MAX15166 are high-efficiency, peak
current-mode, step-down DC-DC converters with inte-
grated high-side (40mI) and low-side (18.5mI) power
switches. The output voltage is set from 0.606V to 0.9 x
V
IN
by using an external resistive divider and can deliver
up to 4A of load current. The input voltage range is 4.5V
to 16V, making these devices ideal for distributed power
systems, notebook computers, nonportable consumer
applications, and preregulation applications.
The devices feature a PWM, internally fixed switching fre-
quency of 500kHz (MAX15066) and 350kHz (MAX15166)
with a 90% maximum duty cycle. PWM current-mode
control allows for an all-ceramic capacitor solution. The
devices include a high gain transconductance error
amplifier. The current-mode control architecture simplifies
compensation design, and ensures a cycle-by-cycle cur-
rent limit and fast reaction to line and load transients. The
low R
DS-ON
, internal MOSFET switches ensure high effi-
ciency at heavy loads and minimize critical inductances,
reducing layout sensitivity.
The devices feature thermal shutdown, overcurrent
protection (high-side sourcing and hiccup protection),
and an internal 5V (25mA) LDO with undervoltage lock-
out. An externally adjustable voltage soft-start gradu-
ally ramps up the output voltage and reduces inrush
current. At light loads, as soon as a low-side MOSFET
zero-crossing event is detected, the devices auto-
matically switch to pulse-skipping mode to keep the
quiescent supply current low and enhances the light load
efficiency. An independent enable input controls and the
power-good output allow for flexible power sequencing.
The devices also provide the ability to start up into a
prebiased output.
Controller Function—PWM Logic
and Skip Mode
The devices employ PWM control with a constant
switching frequency of 500kHz (MAX15066) or 350kHz
(MAX15166) at medium and heavy loads, and skip mode
at light loads. When EN is high, after a brief settling time,
PWM operation starts when V
SS
exceeds the FB voltage,
at the beginning of soft-start.
The first operation is always a high-side turn-on at the
beginning of the clock cycle. The high side is turned off
when any of the following conditions occur:
1) COMP voltage exceeds the internal current-mode
ramp waveform, which is the sum of the slope com-
pensation ramp and the current-mode ramp derived
from the inductor current waveform (through the
current-sense block).
2) The high-side current limit is reached.
3) The maximum duty cycle of 90% is reached.
The low side turns off when the clock period ends or
when the zero-crossing current threshold is intercepted.
The devices monitor the inductor current during every
switch cycle and automatically enters discontinuous
mode when the inductor current valley intercepts the
zero-crossing threshold (under light loads); under very
light load conditions, skip mode is activated/deactivated
on a cycle-by-cycle basis.
Figure 1. Reference Circuit
FB
COMP
22µF
2.2µH
1µF
C
OUT
270pF
C
COMP
10nF
10nF
10kI
R1
R
COMP
10kI
BST
LX
GND
V
DD
PGOOD
IN
EN
SS
INPUT
4.5V TO 16V
OUTPUT
MAX15066
MAX15166
COMPONENT
C
OUT
R
COMP
C
COMP
V
OUT
R1
MAX15066
1 x 47µF 4 x 47µF
1.8V 0.9V
2700pF 2700pF
7.5kI 7.5kI
20kI 5.1kI
MAX15166