MAX15021 datasheet(11/24 Pages) MAXIM

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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 VOUT2 to coincidentally track

VOUT1, connect the same resistive divider used for

FB2, from VOUT1 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 MAX15021 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 hiccup mode, the master will

soft-stop. When the master is shorted and the part

enters in hiccup mode, the slave will ratiometrically soft-

stop. Coming out of hiccup mode, both outputs will soft-

start coincidently or ratiometrically depending on their

initial configuration. During the thermal shutdown or

power-off when the input falls below its UVLO, the out-

put voltages decrease at a rate 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).

Dual, 4A/2A, 4MHz, Step-Down DC-DC

Regulator with Tracking/Sequencing Capability

MAX15021

Maxim Integrated

VRIN1

EN2

EN1

SEL

AVIN

OUTPUT 1 IS THE MASTER AND

OUTPUT 2 IS THE SLAVE.

RATIOMETRIC TRACKING

COINCIDENT TRACKING

SEL

AVIN

OUTPUT 1 IS THE MASTER AND

OUTPUT 2 IS THE SLAVE.

VRIN1

EN1

VOUT1

EN2

VOUT2

FB2

SEL

UNCONNECTED

OUTPUT 2 IS THE MASTER AND

OUTPUT 1 IS THE SLAVE.

VRIN2

EN2

VOUT2

EN1

VOUT1

FB1

VRIN2

EN1

EN2

SEL

UNCONNECTED

OUTPUT 2 IS THE MASTER AND

OUTPUT 1 IS THE SLAVE.

Figure 2. Ratiometric Tracking and Coincident Tracking Configurations

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