MAX15021 Datasheet, PDF (10/24 Pages) Maxim Integrated Products – Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability

MAX15021
Dual, 4A/2A, 4MHz, Step-Down DC-DC
Regulator with Tracking/Sequencing Capability
Detailed Description
The MAX15021 incorporates dual-output, PWM, step-
down, DC-DC regulators with tracking and sequencing
options. The device operates over the input-voltage
range of 2.5V to 5.5V. Each PWM regulator provides an
adjustable output down to 0.6V and delivers up to 4A
(regulator 1) and 2A (regulator 2) of load current. The
high switching frequency (up to 4MHz) and integrated
power switches optimize the MAX15021 for high-perfor-
mance and small-size power management solutions.
Each of the MAX15021 PWM regulator sections utilizes
a voltage-mode control scheme for good noise immuni-
ty and offers external compensation allowing for maxi-
mum flexibility with a wide selection of inductor values
and capacitor types. The device operates at a fixed
switching frequency that is programmable from 500kHz
to 4MHz with a single resistor. Operating the regulators
with 180° out-of-phase clocking, and at frequencies up
to 4MHz, significantly reduces the RMS input ripple
current. The resulting peak input current reduction (and
increase in the ripple frequency) significantly reduces
the required amount of input bypass capacitance.
The MAX15021 provides coincident tracking, ratiomet-
ric tracking, or sequencing to allow tailoring of power-
up/power-down sequence depending on the system
requirements. When sequencing, it powers up glitch-
free into a prebiased output.
The MAX15021 includes internal undervoltage lockout
with hysteresis, digital soft-start/soft-stop for “glitch-free”
power-up and power-down. Protection features include
lossless, cycle-by-cycle current limit, hiccup-mode out-
put short-circuit protection, and thermal shutdown.
Undervoltage Lockout (UVLO)
The supply voltage (V_AVIN) must exceed the default
UVLO threshold before any operation starts. The UVLO
circuitry keeps the MOSFET drivers, oscillator, and all
the internal circuitry shut down to reduce current con-
sumption. The UVLO rising threshold is 2.2V (typ) with
a 120mV (typ) hysteresis.
Digital Soft-Start/Soft-Stop
The MAX15021 soft-start feature allows the load volt-
age to ramp up in a controlled manner, eliminating out-
put-voltage overshoot. Soft-start begins after V_AVIN
exceeds the undervoltage lockout threshold and the
enable input is above 1.225V (typ). The soft-start cir-
cuitry ramps up the reference voltage, controlling the
rate of rise of the output voltage, and reducing input
surge currents during startup. The soft-start duration is
4096 clock cycles. The output voltage is incremented
through 64 equal steps. The output reaches regulation
when soft-start is completed, regardless of the output
capacitance and load.
For tracking applications, soft-stop commences when the
enable input falls below 1.1V (typ). The soft-stop circuitry
ramps down the reference voltage controlling the output-
voltage rate of fall. The output voltage is decremented
through 64 equal steps in 4096 clock cycles.
Oscillator
Use an external resistor at RT to program the
MAX15021 switching frequency from 500kHz to 4MHz.
Calculate the appropriate resistor at RT for the desired
output switching frequency (f_SW):
R_T[kΩ]
=
f_SW[kHz] × 1.067[V]
32[μA] × 4[MHz]
Tracking/Sequencing
The MAX15021 features coincident/ratiometric tracking
and sequencing (see Figure 1). Connect SEL to ground
to configure the device as sequencer. Connect SEL to
AVIN for tracking with output 1 as the master. Leave SEL
unconnected for tracking with output 2 as the master.
Assign the output with the higher voltage as the master.
VOUT1
VOUT2
SOFT-START
SOFT-START
SOFT-STOP
a) COINCIDENT TRACKING OUTPUTS
VOUT1
VOUT2
SOFT-STOP
b) RATIOMETRIC TRACKING OUTPUTS
VOUT1
VOUT2
SOFT-START
SOFT-STOP
c) SEQUENCED OUTPUTS
Figure 1. Graphical Representation of Coincident Tracking,
Ratiometric Tracking, and Sequencing
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Maxim Integrated