Rainbow Electronics MAX1625 - Manual (Page 12)

MAX1624/MAX1625
High-Speed Step-Down Controllers with
Synchronous Rectification for CPU Power
12 ______________________________________________________________________________________
AVX (803) 946-0690 (803) 626-3123
Coilcraft (847) 639-6400 (847) 639-1469
Dale Inductors (605) 668-4131 (605) 665-1627
Coiltronics (561) 241-7876 (561) 241-9339
International
Rectifier
(310) 322-3331 (310) 322-3332
Central
Semiconductor
(516) 435-1110 (516) 435-1824
IRC (512) 992-7900 (512) 992-3377
Matsuo (714) 969-2491 (714) 960-6492
Motorola (602) 303-5454 (602) 994-6430
Murata-Erie (814) 237-1431 (814) 238-0490
Nichicon (847) 843-7500 (847) 843-2798
NIEC (805) 867-2555* [81] 3-3494-7414
Sanyo (619) 661-6835 [81] 7-2070-1174
Siliconix (408) 988-8000 (408) 970-3950
SUPPLIER USA PHONE FACTORY FAX
Sprague (603) 224-1961 (603) 224-1430
Sumida (847) 956-0666 [81] 3-3607-5144
* Distributor
† See Table 4 for a complete listing.
D4 D2 D0
1 0 1
1 1 0
1 — —
1 1 1
1 0 0
0 0 0
0 0 1
0 — —
0 1 1
0 0 0
0 — —
0 1 0
0 1 1
D3
0
1
—
1
0
0
0
0
0
1
1
1
1
D1
0
1
—
1
0
0
0
—
1
0
—
1
1
OUTPUT
VOLTAGE
(V)
3.4
2.1
Decreases
in 100mV
increments
No CPU (OFF)
3.5
1.9
1.8
Decreases
in 100mV
increments
1.2
1.1
1.1
1.1
No CPU (OFF)
COMPATIBILITY
Intel-compatible
codes
Non-Intel
compatible codes
Table 2. Component Suppliers Table 3. MAX1624 Output Voltage
Adjustment Settings (Abbreviated
† )
_____Standard Application Circuits
The predesigned MAX1624/MAX1625 circuits shown in
Figures 1 and 2 meet a wide range of applications with
output currents up to 12A and higher. Use Table 1 to
select components appropriate for the desired output
current range, and adapt the evaluation kit PC board
layout as necessary. Table 2 lists suggested vendors.
These circuits represent a good set of trade-offs
between cost, size, and efficiency while staying within
the worst-case specification limits for stress-related
parameters, such as capacitor ripple current.
These MAX1624/MAX1625 circuits were designed for
the specified frequencies. Do not change the switching
frequency without first recalculating component val-
ues—particularly the inductance, output filter capaci-
tance, and RC1 resistance values. Recalculate the
voltage-feedback resistor and compensation-capacitor
values (CC1 and CC2) as necessary to reconfigure
them for different output voltages. Table 3 lists voltage
adjustment DAC codes for the MAX1624.
_______________Detailed Description
The MAX1624/MAX1625 are BiCMOS switch-mode,
power-supply controllers designed for buck-topology
regulators. They are optimized for powering the latest
high-performance CPUs—demanding applications
where output voltage precision, good transient
response, and high efficiency are critical for proper
operation. With appropriate external components, the
MAX1624/MAX1625 deliver over 15A between 1.1V and
3.5V with ±1% accuracy. The MAX1625 offers 1% typi-
cal transient-load regulation from a +5V supply, while the
MAX1624 offers a selectable transient-load regulation of
0.5%, 1%, or 2%. Remote output sensing ensures volt-
age precision by eliminating errors caused by PC board
trace impedance. These controllers achieve 90% effi-
ciency by using synchronous rectification.
A typical application circuit consists of two N-channel
MOSFETs, a rectifier, and an LC output filter (Figure 1).
At each of the internal oscillator’s rising edges, the
high-side MOSFET switch (N1) is turned on and allows
current to ramp up through the inductor to the output
filter capacitor and load, storing energy in a magnetic
field. The current is monitored by reading the voltage