MAX1544 Datasheet, PDF (16/42 Pages) Maxim Integrated Products – Dual-Phase, Quick-PWM Controller for AMD Hammer CPU Core Power Supplies

Dual-Phase, Quick-PWM Controller for
AMD Hammer CPU Core Power Supplies
Pin Description (continued)
PIN
NAME
FUNCTION
32
DLS
Secondary Low-Side Gate-Driver Output. DLS swings from PGND to V_DD. DLS is forced high after the
MAX1544 powers 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
Detailed Description
Dual 180° Out-of-Phase Operation
The two phases in the MAX1544 operate 180° out-of-
phase (SKIP = REF or high) to minimize input and output
filtering requirements, reduce electromagnetic interfer-
ence (EMI), and improve efficiency. This effectively low-
ers component count—reducing cost, board space, and
component power requirements—making the MAX1544
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 I²R 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, to reduce ESR-related power losses, and to meet
the necessary RMS ripple current rating.
With the MAX1544, the controller shares the current
between two phases that operate 180° out-of-phase, so
the high-side MOSFETs never turn on simultaneously
during normal operation. The instantaneous input cur-
rent 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 sec-
tion). As a result, the same performance can be
achieved with fewer or less-expensive input capacitors.
Table 1 lists component selection for standard multi-
phase selections and Table 2 is a list of component
suppliers.
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 degrees
out-of-phase when a transient occurs actually respond
slower than an equivalent single-phase controller. In
order to provide fast transient response, the MAX1544
supports a phase-overlap mode, which allows the dual
regulators to operate in-phase when heavy-load tran-
sients are detected, reducing the response time. After
either high-side MOSFET turns off, if the output voltage
does not exceed the regulation voltage when the mini-
mum off-time expires, the controller simultaneously
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 out-
put voltage exceeds the regulation voltage after the
minimum off-time expires.
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