Rainbow Electronics MAX15022 - Manual (Page 13)

MAX15022
Dual, 4A/2A, 4MHz, Step-Down DC-DC
Regulator with Dual LDO Controllers
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Coincident/Ratiometric Tracking
The enable inputs in conjunction with digital soft-start
and soft-stop provide coincident/ratiometric tracking.
Track an output voltage by connecting a resistive
divider from the output being tracked to its enable
input. For example, for V
OUT2 to coincidentally track
V OUT1 , connect the same resistive divider used for
FB2, from V OUT1 to EN2 to SGND (see Figure 2).
Track ratiometrically by connecting EN_ to SGND. This
synchonizes the soft-start and soft-stop of all the regu-
lator references, and hence their respective output volt-
ages will track ratiometrically (see Figure 2).
When the MAX15022 regulators are configured as volt-
age trackers, output short-circuit fault conditions at
either master or slave output are handled carefully—nei-
ther the master nor slave output will remain energized
when the other output is shorted to ground. When the
slave is shorted and enters into hiccup mode, the mas-
ter will soft-stop. When the master is shorted and the
part enters into hiccup mode, the slave will ratiometrical-
ly soft-stop. Coming out of hiccup mode, both outputs
will soft-start coincidently or ratiometrically depending
on their initial configuration. During the thermal shut-
down or power-off when the input falls below its UVLO,
the output voltages track down depending on the
respective output capacitance and load.
See Figure 1 for a graphical representation of coinci-
dent/ratiometric tracking.
Sequencing
When sequencing, the voltage at the enable inputs
must exceed 1.225V (typ) for each PWM controller to
start (see Figure 1c).
V PVIN1
EN2
EN1
SEL AVIN
OUTPUT 1 IS THE MASTER AND
OUTPUT 2 IS THE SLAVE.
RATIOMETRIC TRACKING a) b) c) COINCIDENT TRACKING COINCIDENT TRACKING
SEL AVIN
OUTPUT 1 IS THE MASTER AND
OUTPUT 2 IS THE SLAVE.
V PVIN1
R A
R B
R A
R B
EN1
V OUT1
EN2
V OUT2
FB2
SEL UNCONNECTED
OUTPUT 2 IS THE MASTER AND
OUTPUT 1 IS THE SLAVE.
V PVIN2
R C
R D
R C
R D
EN2
V OUT2
EN1
V OUT1
FB1
V PVIN2
EN1
EN2
SEL UNCONNECTED
OUTPUT 2 IS THE MASTER AND
OUTPUT 1 IS THE SLAVE.
Figure 2. Ratiometric Tracking and Coincident Tracking Configurations