MAX8664
Low-Cost, Dual-Output, Step-Down
Controller with Fast Transient Response
18 ______________________________________________________________________________________
Power-Up and Sequencing
The MAX8664 features an OSC/EN12 input that is used
both for setting the switching frequency and as an
enable input for both controllers. A resistor from
OSC/EN12 to GND sets the switching frequency, and
when OSC/EN12 is high impedance, both controllers
enter low-power shutdown mode. This is easily
achieved with a transistor between the resistor and
GND. Figure 6a shows the startup configuration with
independent outputs. With REFIN2 connected to V
CC
,
both controllers use the internal reference.
For tracking applications, connect REFIN2 to the center
of a resistive voltage-divider between the output of con-
troller 1 and GND. See Figure 6b. In this application,
the output of regulator 2 tracks the output voltage of
controller 1. The voltage-divider resistors set the
V
OUT2
/V
OUT1
ratio. A typical tracking application is for
the VTT supply of DDR memory.
Figure 6c shows one method of sequencing the out-
puts. Output 1 rises first. When PWRGD goes high, the
transistors allow the external reference to drive REFIN2
and output 2 rises. The circuit in Figure 6d functions
similarly, except the enable signal is supplied externally
instead of being driven by the PWRGD signal.
Table 5. Component List for Figure 5
