Detailed Description
DC-to-DC PWM Controller
The MAX8529 step-down converter uses a PWM volt-
age-mode control scheme (Figure 2) for each out-of-
phase controller. The controller generates the clock
signal by dividing down the internal oscillator or SYNC
input when driven by an external clock, so each con-
troller’s switching frequency equals half the oscillator fre-
quency (f
SW
= f
OSC
/ 2). An internal transconductance
error amplifier produces an integrated error voltage at
the COMP pin, providing high DC accuracy. The voltage
at COMP sets the duty cycle using a PWM comparator
and a ramp generator. At each rising edge of the clock,
REG1’s high-side n-channel MOSFET turns on and
remains on until either the appropriate duty cycle or until
the maximum duty cycle is reached. REG2 operates out-
of-phase, so the second high-side MOSFET turns on at
each falling edge of the clock. During each high-side
MOSFET’s on-time, the associated inductor current
ramps up.
During the second-half of the switching cycle, the high-
side MOSFET turns off and the low-side n-channel
MOSFET turns on. Now the inductor releases the stored
energy as its current ramps down, providing current to
the output. Under overload conditions, when the induc-
tor current exceeds the selected valley current limit
(see the Current-Limit Circuit (ILIM_) section), the high-
side MOSFET does not turn on at the appropriate clock
edge and the low-side MOSFET remains on to let the
inductor current ramp down.
Synchronized Out-of-Phase Operation
The two independent regulators in the MAX8529 operate
180 degrees out-of-phase to reduce input filtering
requirements, reduce electromagnetic interference (EMI),
and improve efficiency. This effectively lowers component
cost and saves board space, making the MAX8529 ideal
for cost-sensitive applications.
Dual-switching regulators typically operate both
controllers in-phase, and turn on both high-side MOSFETs
at the same time. The input capacitor must then support
the instantaneous current requirements of both controllers
simultaneously, resulting in increased ripple voltage and
current when compared to a single switching regulator.
The higher RMS ripple current lowers efficiency due to
power loss associated with the input capacitor’s effective
series resistance (ESR). This typically requires more low-
ESR input capacitors in parallel to minimize input voltage
ripple and ESR-related losses, or to meet the necessary
ripple-current rating.
MAX8529
1.5MHz Dual 180° Out-of-Phase
PWM Step-Down Controller with POR
_______________________________________________________________________________________ 7
Pin Description (continued)
External Inductor Connection for Regulator 1 (REG1). Connect LX1 to the switched side of the
inductor. LX1 serves as the lower supply rail for the DH1 high-side gate driver.
Boost Flying-Capacitor Connection for Regulator 1 (REG1). Connect BST1 to an external ceramic
capacitor and diode according to Figure 1.
.
Internal 5V Linear-Regulator Output. Supplies the regulators and powers the low-side gate drivers
and external boost circuitry for the high-side gate drivers.
.
Boost Flying-Capacitor Connection for Regulator 2 (REG2). Connect BST2 to an external ceramic
capacitor and diode according to Figure 1.
External Inductor Connection for Regulator 2 (REG2). Connect LX2 to the switched side of the
inductor. LX2 serves as the lower supply rail for the DH2 high-side gate driver.
Active-High Enable Input. A logic low shuts down both controllers. Connect to V
operation.
