Dual, Interleaved, Fixed-Frequency Step-Down Controller with a Dynamically Adjustable Output
Dual, Interleaved, Fixed-Frequency Step-Down Controller with a Dynamically Adjustable Output Designed for Generation of Low-Voltage Chipset and RAM Power Supplies in Notebook Computers
The MAX1549 dual pulse-width modulation (PWM) stepdown
controller provides the high efficiency, excellent
transient response, and high DC-output accuracy necessary
for generating low-voltage chipset and RAM
power supplies in notebook computers. The controller
employs a fixed-frequency, current-mode PWM architecture
that does not require complex compensation.
The MAX1549 also interleaves the dual step-down regulators,
minimizing the input capacitor requirements.
The MAX1549 features differential current-sense inputs
for accurately sensing the inductor current across an
external current-sense resistor in series with the output
to ensure reliable overload protection. Alternatively, the
controller can provide overload protection using lossless
inductor current-sensing methods, lowering power
dissipation and reducing system cost.
Single-stage buck conversion allows the MAX1549 to
directly step down high-voltage batteries for the highest
possible efficiency. Very low output-voltage applications
require two-stage conversion—stepping down
from another system supply rail instead of the battery.
The MAX1549 powers chipsets and graphics processor
cores that require dynamically adjustable output voltages,
or generates the active termination bus that must track
the input reference. The main step-down controller
(OUT1) regulates the dedicated reference input (REFIN)
voltage generated by a resistive voltage-divider from the
MAX1549's reference. The MAX1549 also includes internal
open-drain pulldowns with logic-level control inputs to
dynamically adjust the REFIN resistive-divider ratio. When
a transition occurs on these control inputs, the controller
enters forced-PWM mode and blanks the power-good
(PGOOD1) output and output fault protection. OUT2 uses
a Dual-Mode™ feedback input to provide either fixed
2.5V/1.8V or adjustable output voltage regulation. The
MAX1549 is available in a 40-pin, 6mm x 6mm thin QFN
package.
Key Features
Applications/Uses
Interleaved, Fixed-Frequency, Current-Mode Control Architecture
1% VOUT Accuracy Over Line and Load
Main Output (OUT1)
0.5V to 2.0V Adjustable Output
External Reference Input for Dynamically Selectable Output Voltages
Four Digitally Selectable Output Voltages
Power-Good and Fault Blanking During Transitions
Second Output (OUT2)
2.5V/1.8V Fixed or 0.5V to 2.7V Adjustable Output
Accurate Differential Current-Sense Inputs
100kHz/200kHz/300kHz/400kHz Selectable Switching Frequency
Output Overvoltage/Undervoltage Protection
Soft-Start and Soft-Shutdown
Drives Large Synchronous-Rectifier FETs
2V ±0.6% Reference Output
Separate Enable Inputs with Accurate Threshold Voltages
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