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

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

11

EN2

EN1

SEL

AVIN

OUTPUT 1 IS THE MASTER AND

OUTPUT 2 IS THE SLAVE.

RATIOMETRIC TRACKING

COINCIDENT TRACKING

COINCIDENT TRACKING

SEL

AVIN

OUTPUT 1 IS THE MASTER AND

OUTPUT 2 IS THE SLAVE.

EN1

EN2

FB2

SEL

UNCONNECTED

OUTPUT 2 IS THE MASTER AND

OUTPUT 1 IS THE SLAVE.

EN2

EN1

FB1

EN1

EN2

SEL

UNCONNECTED

OUTPUT 2 IS THE MASTER AND

OUTPUT 1 IS THE SLAVE.

Figure 2. Ratiometric Tracking and Coincident Tracking Configurations