MAX15002 Datasheet, PDF (14/30 Pages) Maxim Integrated Products – Dual-Output Buck Controller with Tracking/Sequencing

Dual-Output Buck Controller with
Tracking/Sequencing
Coincident/Ratiometric
Tracking (SEL, EN/TRACK2)
The enable/tracking input in conjunction with digital
soft-start and soft-stop provides coincident/ratiometric
tracking. See Figure 1. Track an output voltage by con-
necting 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/TRACK2 to
SGND. This synchonizes the soft-start and soft-stop of all
the controllers’ references, and hence their respective
output voltages will track ratiometrically. See Figure 2
and the Ratiometric Startup and Ratiometric Shutdown
graphs in the Typical Operating Characteristics.
Connect SEL to REG to configure as a dual tracker.
When the MAX15002 converter is configured as a
tracker, the output short-circuit fault situations at master
or slave output is handled carefully so that either the
master or slave output does not stay on when the other
output is shorted to the ground. When the slave is
shorted and enters in 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 the hiccup, all outputs will soft-start coin-
cidently or ratiometrically depending on their initial con-
figuration. See the Typical Operating Characteristics for
the output behaviour during the fault conditions. During
the thermal shutdown or power-off, when the input falls
below its UVLO, the output voltages fall down at the
rate depending on the respective output capacitor and
load. See Figure 1.
Output-Voltage Sequencing
(SEL, EN/TRACK2, 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/TRACK2
inputs can be daisy-chained to generate power sequenc-
ing. Open-drain PGOOD_ outputs go high impedance
when FB_ is above the PGOOD_ threshold (555mV typ).
V_OUT1
V_OUT2
SOFT-START
SOFT-STOP
A) COINCIDENT TRACKING OUTPUTS
V_OUT1
V_OUT2
SOFT-START
SOFT-STOP
B) RATIOMETRIC TRACKING OUTPUTS
V_OUT1
V_OUT2
SOFT-
START
SOFT-STOP
C) SEQUENCED OUTPUTS
Figure 1. Graphical Representation of Coincident Tracking,
Ratiometric Tracking, and PGOOD Sequencing
Connect the power-good output to the enable/tracking
input to set when the other controller will start. See
Figure 2. Connect SEL to SGND to configure as a dual
sequencer.
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