High-current buck regulators deliver efficiency of 97 percent for high-performance FPGAs, and ASICs
Members of National’s PowerWise energy-efficient product family, the LM21212-1 and LM21215 high-current buck regulators feature integrated high-side and low-side FETs, which simplify design and reduce solution size. The LM21212-1 features an output current up to 12 amps with synchronizable switching frequency and the LM21215 provides a resistor-programmable current limit, allowing up to 15 amps of continuous output current, offering the industry’s best power density. Both products provide peak efficiency greater than 97 percent from a 5 V input to 3.3 V output, and greater than 92 percent efficiency when regulating a 1.2 V output from a 5 V input.
Under typical operating conditions such as 5 Vin, 1.2 Vout, 10 A, 500 kHz and 25 degrees C ambient, the regulators provide a three percent to five percent efficiency improvement and up to 10 degrees C cooler case temperature than similar products on the market today.
The LM21212-1 and LM21215 are monolithic synchronous buck regulators offered in a small 4.4 mm by 6.5 mm by 0.9 mm package. The LM21212-1 is capable of delivering up to 12 A of continuous output current with a switching frequency that can be synchronized to an external oscillator between 300 kHz and 1.5 MHz. The LM21215 features a fixed 500 kHz switching frequency and is capable of delivering up to 15 A.
The regulators are optimized to work over an input voltage range of 2.95 V to 5.5 V and produce an output voltage down to 0.6 V with superior efficiency. The voltage-mode control loop provides high noise immunity and narrow duty cycle and can be compensated to be stable with any type of output capacitor for maximum flexibility and ease-of-use. A programmable over-current protection feature allows a user to specify the peak current level. An internal over voltage protection circuit provides increased system reliability, while a precision enable pin and integrated UVLO allow turn-on of the device to be tightly controlled and sequenced.
Start-up inrush currents are limited by both an internally fixed and externally adjustable soft-start circuit. Both regulators provide a monotonic start-up into a pre-biased load, preventing the devices from sinking current until the internal soft-start ramp exceeds the voltage at the feedback pin. Fault detection and supply sequencing are also possible with the integrated power good circuit. The regulators are designed to work well in multi-rail power supply architectures, as the output voltage can be configured to track a higher voltage rail using the SS/TRK pin.
Availability and Pricing
National’s new buck regulators are available now and offered in 20-pin thermally-enhanced TSSOP packages. Priced in quantities of 1,000, the LM21212-1 is $3.85 and the LM21215 is $4.15. A version of the LM21212-1 with adjustable switching frequency will be available in March 2011.
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