Rainbow Electronics MAX15022 - Manual (Page 12)

MAX15022
Dual, 4A/2A, 4MHz, Step-Down DC-DC
Regulator with Dual LDO Controllers
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Detailed Description
The MAX15022 incorporates dual-output, PWM, step-
down, DC-DC regulators and dual LDO controllers 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
MAX15022 for high-performance and small-size power
management solutions.
Each of the MAX15022 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 MAX15022 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 MAX15022 features
two LDO controllers for external PNP pass transistors to
provide two additional outputs.
The MAX15022 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 MAX15022 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
MAX15022 switching frequency from 500kHz to 4MHz.
Calculate the appropriate resistor value at RT for the
desired output switching frequency (f
SW ):
Tracking/Sequencing
The MAX15022 features coincident/ratiometric tracking
and sequencing (see Figure 1). Connect SEL to ground
to configure the device as a 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.
R k
A
T
[ ]
.
[ ]
Ω =
Ч
Ч
f [kHz] 1 [V]
4[MHz]
SW
067
32 μ
V OUT1
SOFT-START
SOFT-START
SOFT-START
SOFT-STOP
a) COINCIDENT TRACKING OUTPUTS
b) RATIOMETRIC TRACKING OUTPUTS
c) SEQUENCED OUTPUTS
SOFT-STOP
SOFT-STOP
V OUT2
V OUT1
V OUT2
V OUT1
V OUT2
Figure 1. Graphical Representation of Coincident Tracking,
Ratiometric Tracking, and Sequencing