Rainbow Electronics MAX1545 - Manual (Page 16)

MAX1519/MAX1545
Dual-Phase, Quick-PWM Controllers for
Programmable CPU Core Power Supplies
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Detailed Description
Dual 180° Out-of-Phase Operation
The two phases in the MAX1519/MAX1545 operate
180° out-of-phase (SKIP = REF or high) to minimize
input and output filtering requirements, reduce electro-
magnetic interference (EMI), and improve efficiency.
This effectively lowers component count—reducing
cost, board space, and component power require-
ments—making the MAX1519/MAX1545 ideal for high-
power, cost-sensitive applications.
Typically, switching regulators provide transfer power
using only one phase instead of dividing the power
among several phases. In these applications, the input
capacitors must support high instantaneous current
requirements. The high-RMS ripple current can lower
efficiency due to I
2 R power loss associated with the input
capacitor’s effective series resistance (ESR). Therefore,
the system typically requires several low-ESR input
capacitors in parallel to minimize input voltage
ripple, reduce ESR-related power losses, and to meet
the necessary RMS ripple current rating.
With the MAX1519/MAX1545, the controller shares the
current between two phases that operate 180° out-of-
phase, so the high-side MOSFETs never turn on simul-
taneously during normal operation. The instantaneous
input current of either phase is effectively cut in half,
resulting in reduced input voltage ripple, ESR power
loss, and RMS ripple current (see the Input Capacitor
Selection section). As a result, the same performance
can be achieved with fewer or less expensive input
capacitors.
Transient Overlap Operation
When a transient occurs, the response time of the con-
troller depends on how quickly it can slew the inductor
current. Multiphase controllers that remain 180° out-of-
phase when a transient occurs actually respond slower
than an equivalent single-phase controller. In order to
provide fast transient response, the MAX1519/
MAX1545 support a phase-overlap mode, which allows
the dual regulators to operate in-phase when heavy
load transients are detected, reducing the response
time. After either high-side MOSFET turns off and if the
output voltage does not exceed the regulation voltage
when the minimum off-time expires, the controller simul-
taneously turns on both high-side MOSFETs during the
next on-time cycle. This maximizes the total inductor-
current slew rate. The phases remain overlapped until
the output voltage exceeds the regulation voltage and
after the minimum off-time expires.
After the phase-overlap mode ends, the controller auto-
matically begins with the opposite phase. For example, if
the secondary phase provided the last on-time pulse
before overlap operation began, the controller starts
switching with the main phase when overlap operation
ends.
Pin Description (continued)
PIN NAME FUNCTION
31 PGND Power Ground. Ground connection for low-side gate drivers DLM and DLS.
32 DLS
Secondary Low-Side Gate-Driver Output. DLS swings from PGND to V DD . DLS is forced high after the
MAX1519/MAX1545 power down.
33 DHS Secondary High-Side Gate-Driver Output. Swings LXS to BSTS.
34 LXS
Secondary Inductor Connection. LXS is the internal lower supply rail for the DHS high-side gate
driver.
35 BSTS
Secondary Boost Flying Capacitor Connection. An optional resistor in series with BSTS allows the
DHS pullup current to be adjusted.
36 V+
Battery Voltage-Sense Connection. Used only for PWM one-shot timing. DH_ on-time is inversely
proportional to input voltage over a range of 4V to 28V.
37 CMP Main Inductor Positive Current-Sense Input
38 CMN Main Inductor Negative Current-Sense Input
39 CSN Secondary Inductor Positive Current-Sense Input
40 CSP Secondary Inductor Negative Current-Sense Input