Datasheet

MAX8855/MAX8855A
Dual, 5A, 2MHz Step-Down Regulators
______________________________________________________________________________________ 11
Figure 3b. Startup and Sequencing Options—Ratiometric Tracking Startup and Shutdown Waveforms V
OUT1
Track V
OUT2
EN
OUT2
OUT1
PWRGD1
PWRGD2
OUT2
EN1
SS2
PWRGD1
EN2
SS1
PWRGD2
V
DD
REFIN
10kΩ
10kΩ
10kΩ 10kΩ
EN
reference with soft-start time set independently by the
SS1 capacitor (see Figure 3a).
For ratiometric tracking applications, connect REFIN to
the center of a voltage-divider from the output of regula-
tor 2 to GND (see Figure 3b). In this application, the EN_
inputs are connected to each other and driven as a sin-
gle enable input. Regulator 2 starts up with a normal soft-
start (C
SS2
sets the time), and regulator 1 output
ratiometrically tracks the regulator 2 output voltage. The
voltage-divider resistors set the V
OUT1
/V
OUT2
ratio (see
the
Setting the Output Voltage section). In Figure 3b,
V
OUT1
regulates to half of V
OUT2
. Note that a capaci-
tance of 1000pF should be connected to SS1 for stability.
Figure 3c shows the output sequencing application
using an external reference.
Figure 3c. Startup and Sequencing Options—Sequencing Startup and Shutdown Waveforms with External Reference
EN1
OUT1
OUT2
PWRGD2
PWRGD1
EN1
SS2
PWRGD1
EN2
SS1
PWRGD2
V
DD
REFIN
REFIN
10kΩ
10kΩ
EN1