MAX15003 Datasheet, PDF (16/32 Pages) Maxim Integrated Products – Triple-Output Buck Controller with Tracking/Sequencing

Triple-Output Buck Controller with
Tracking/Sequencing
Coincident/Ratiometric
Tracking (SEL, EN/TRACK_)
The enable/tracking input in conjunction with digital soft-
start and soft-stop provides coincident/ratiometric track-
ing (see Figure 1). Track an output voltage by
connecting a resistive divider from the output being
tracked to the enable/tracking input. For example, for
V_OUT2 to coincidentally track V_OUT1, connect the same
resistive divider used for FB2, from OUT1 to
EN/TRACK2 to SGND. See Figure 2 and the Coincident
Startup and Coincident Shutdown graphs in the Typical
Operating Characteristics.
Track ratiometrically by connecting EN/TRACK_ to
SGND. This synchonizes the soft-start and soft-stop of
all the controllers’ references, and hence their respec-
tive output voltages track ratiometrically. See Figure 2
and the Typical Operating Characteristics (Ratiometric
Startup and Ratiometric Shutdown graphs).
Connect SEL to REG to configure as a triple tracker.
When the MAX15003 converter is configured as a
tracker, the output short-circuit fault situations at master
or slave outputs are handled carefully so that either the
master or slave output does not stay on when the other
outputs are shorted to the ground. When the slave is
shorted and enters in hiccup mode, both the master
and the other slave soft-stop. When the master is short-
ed and the part enters in hiccup mode, the slaves ratio-
metrically soft-stop. Coming out of the hiccup, all
outputs soft-start coincidently or ratiometrically
depending on their initial configuration. See the Typical
Operating Characteristics for the output behaviour dur-
ing the fault conditions. During power-off, when the
input falls below its UVLO, the output voltages fall down
at the rate depending on the respective output capaci-
tor and load.
Output-Voltage Sequencing
(SEL, EN/TRACK_, PGOOD)
Referring to Figure 1c, when sequencing, the
enable/tracking input must be above 1.24V for each PWM
controller to start. The PGOOD_ outputs and EN/TRACK_
inputs can be daisy-chained to generate power sequenc-
ing. Open-drain PGOOD_ outputs go high impedance
V_OUT1
V_OUT2
V_OUT3
SOFT-START
SOFT-STOP
A) COINCIDENT TRACKING OUTPUTS
V_OUT1
V_OUT2
V_OUT3
SOFT-START
SOFT-STOP
B) RATIOMETRIC TRACKING OUTPUTS
SOFT-
START
V_OUT1
V_OUT2
V_OUT3
SOFT-STOP
C) SEQUENCED OUTPUTS
Figure 1. Graphical Representation of Coincident Tracking,
Ratiometric Tracking, or PGOOD Sequencing
when FB_ is above the PGOOD_ threshold (555mV typ).
Connect a resistive divider from the power-good output to
the enable/tracking input to SGND to set when each con-
troller will start. See Figure 2. Connect SEL to SGND to
configure as a triple sequencer.
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