MAX1540 Datasheet, PDF (22/49 Pages) Maxim Integrated Products – Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear Regulator

Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Table 2. Component Suppliers
SUPPLIER
Central
Semiconductor
PHONE
631-435-1110
(USA)
WEBSITE
www.centralsemi.com
Coilcraft
800-322-2645
(USA)
www.coilcraft.com
Fairchild
Semiconductor
888-522-5372
(USA)
www.fairchildsemi.com
International
Rectifier
310-322-3331
(USA)
www.irf.com
Kemet
Panasonic
Sanyo
Siliconix
(Vishay)
Sumida
408-986-0424
(USA)
65-6231-3226
(Singapore),
408-749-9714
(USA)
619-661-6835
(USA)
203-268-6261
(USA)
408-982-9660
(USA)
www.kemet.com
www.panasonic.com
www.sanyovideo.com
www.vishay.com
www.sumida.com
Taiyo Yuden
03-3667-3408
(Japan),
408-573-4150
(USA)
www.t-yuden.com
847-803-6100
(USA),
TDK
www.component.tdk.com
81-3-5201-7241
(Japan)
TOKO
858-675-8013
(USA)
www.tokoam.com
Standard Application Circuits
The MAX1540 Standard Application Circuit (Figure 1)
generates a 1.8V and 2.5V rail for general-purpose use
in a notebook computer. The MAX1541 Standard
Application Circuit (Figure 12) generates a dynamically
adjustable output voltage (OUT1), typical of a graphics-
processor core requirement, and a fixed 2.5V output
(OUT2).
See Table 1 for component selections. Table 2 lists the
component manufacturers.
Detailed Description
The MAX1540/MAX1541 provide three independent out-
puts with independent enable controls. They contain two
Quick-PWM step-down controllers ideal for low-voltage
power supplies for notebook computers, and a 100mA
linear regulator. Maxim’s proprietary Quick-PWM pulse-
width modulators in the MAX1540/ MAX1541 are specifi-
cally designed for handling fast load steps while
maintaining a relatively constant operating frequency and
inductor operating point over a wide range of input volt-
ages. The Quick-PWM architecture circumvents the poor
load-transient timing problems of fixed-frequency current-
mode PWMs, while also avoiding the problems caused
by widely varying switching frequencies in conventional
constant-on-time and constant-off-time PWM schemes.
The MAX1540 linear regulator draws power from the
battery voltage and generates a preset 5V, which can
be used to bootstrap the buck controllers for automatic
startup. The MAX1541’s linear regulator can be con-
nected to any input source from 4.5V to 28V to gener-
ate an adjustable output voltage as low as 1.25V, or as
high as the input source with 800mV of dropout at
50mA load.
Single-stage buck conversion allows the MAX1540/
MAX1541 to directly step down high-voltage batteries
for the highest possible efficiency. Alternatively, two-
stage conversion (stepping down from another system
supply rail instead of the battery at a higher switching
frequency) allows the minimum possible physical size.
The MAX1540 generates chipset, dynamic random-
access memory (DRAM), CPU I/O, or other low-voltage
supplies down to 0.7V. The MAX1541 powers chipsets
and graphics processor cores that require dynamically
adjustable output voltages, or generates the active ter-
mination bus that must track the input reference. The
MAX1540 is available in a 32-pin thin QFN package
with optional inductor-saturation protection and over-
voltage/undervoltage protection. The MAX1541 is avail-
able in a 40-pin thin QFN package with optional
inductor-saturation protection and overvoltage/under-
voltage protection.
+5V Bias Supply (V_CC and V_DD)
The MAX1540/MAX1541 require a 5V bias supply in
addition to the battery. This 5V bias supply is either the
MAX1540/MAX1541s’ internal linear regulator or the
notebook’s 95%-efficient 5V system supply. Keeping the
bias supply external to the IC can improve efficiency
and allows the fixed 5V or adjustable linear regulator
(MAX1541) to be used for other applications. For the
MAX1540, the gate-driver input supply (V_DD) is connect-
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