Design Challenges: Avoiding the Pitfalls, winning the game - Xilinx

Versatile FPGA Power Solutions from National Semiconductor
LM2743/44 Low-Voltage Synchronous Buck Controllers
3V to 6V
(Bias)
ON
OFF
Output power good
LM2743 Typical application diagram
V CC
SD
PGOOD
LM2743
SS/TRK
EAO GND
HG
ISEN
LG
FB
Input power
1V to 16V
V OUT = O.6V to 0.85 *V IN
Up to 25A loads
• Highly efficient 2A to 25A solution
• Input voltage from 1V to 16V
• Adjustable output voltage as low as 0.6V
• Power-good flag and output enable
• 1.5% reference accuracy over temperature
• Current limit without sense resistor
• Programmable softstart
• Switching frequency from 50 kHz to 1 MHz
• Available in small TSSOP-14 packaging
The LM2743 and LM2744 are high-speed synchronous buck regulator
controllers that drive external MOSFETs to supply as much
as 25A of current. They can provide simple down conversion to
output voltages as low as 0.6V. Although the control sections of the
ICs are rated for 3 to 6V, the driver sections are designed to accept
input supply rails as high as 16V. The use of adaptive non-overlapping
MOSFET gate drivers helps avoid potential shoot-through
problems while maintaining high efficiency.
A wide range of switching frequencies from 50 kHz to 1 MHz
gives Xilinx ® FPGA and system power supply designers the flexibility
to make better trade-offs between component size, cost, and efficiency.
A versatile softstart and tracking pin allows ratiometric,
coincidental, or offset tracking, which are critical for FPGA systems.
An evaluation board is available.
For free samples, evaluation boards, or more information,
visit power.national.com or call 1-800-272-9959.
• Complete, easy-to-use switcher solution has the smallest footprint
and highest power density in the industry
• Choice of switching frequencies allows designers to
trade-off efficiency against solution size and EMI
• Current mode control improves phase margin, line regulation,
and rejection of transients
• Internal softstart circuitry, cycle-by-cycle, thermal shutdown, and over-voltage protection
The LM2734 and LM2736 are monolithic, high-frequency (550
kHz and 1.6 MHz) PWM step-down DC/DC converters in tiny sixpin
thin SOT-23 packaging. They provide local DC/DC conversion
for Xilinx FPGAs with currents up to 1A.
Both regulators need no external compensation and are supported
by WEBENCH ®, National’s online design tool. The ability to drive
up to 1A loads with an internal 300 mΩ NMOS switch using stateof-the-art
0.5 µm BiCMOS technology results in the best power density
available. The world-class control circuitry supports exceptionally
high frequency conversion over the entire 3V to 20V input operating
range, down to the minimum output voltage of 0.8V. Even though
the operating frequencies are very high, efficiencies as high as 90% are
easy to achieve. Additionally, a current-mode control loop provides
fast transient response and accurate regulation in the smallest possible
PCB area. An evaluation board is available.
Third Quarter 2005 Xcell Journal 63
5V
VIN
OFF
C1
10 µF
ON
(3V to 18V)
LM2734 Typical application diagram
VIN
EN
SW
LM2734
GND
BOOST
FB
POWER MANAGEMENT
LM2734/36 1A SOT-23 Buck Regulators
D1
C2
0.01 µF
D2
L1
10 µH
R1
31.6 kΩ
R2
10 kΩ
(Down to 0.8V)
V OUT
3.3V/1A
C3
10 µF
Feature LM2734 LM2736
Input Range 3.0V to 20V 3.0V to 18V
Output Load 1A 750 mA
Output Range 0.8V to 18V 1.25V to 16V
Internal References 0.8V, 2% 1.25V, 2%
Operating Frequency 550 kHz/1.6 MHz/3 MHz