lowPOWERZONE Products for the week of February 20, 2006
Advanced Analogic Technologies Says . . .
AAT1146/2512: Dc-Dc Converters For Mobile Applications
Fast Transient Response Supports Demanding Load Swings in
GSM Phones
Advanced Analogic Technologies Incorporated (AnalogicTech), a developer
of power management semiconductors for mobile consumer electronic devices,
today introduced two new DC/DC converters for portable systems powered by
single-cell lithium-ion/polymer batteries. Optimized for extremely fast
transient response, the AAT1146 and AAT2512 step-down converters are ideally
suited for GSM phone applications.
"The power supply supporting a GSM phone baseband chipset must almost
instantaneously ramp from a few milliamps to full load, so extremely fast
transient response is critical," notes David Brown, Senior Manager
of Applications Engineering for AnalogicTech. "The AAT1146 and AAT2512
devices allow design engineers to easily meet these stringent requirements,
while keeping the converter output in regulation."
analogZONE Says...
The story here is transient response and these converters offer a typical turn-on time of 150 µs, an important factor in applications where the current drain demand goes from virtually nothing to full power, and the 400 mA per channel that these parts offer will make them very attractive in transmit applications particularly.
Although not shown on the "typical application" block on the front of the data sheet these parts use the normal resistive divider to the feedback pin to compare the output voltage to the internal reference, in this case 0.6 V. The higher end of the output voltage range is equal to the input voltage. That input voltage range is 2.7 V to 5.5 V -- an ideal span for single cell Li-Ion/Polymer applications.
There is an internal soft-start, the switching frequency is a fixed 1.4 MHz and the p-channel MOSFET(s) have a current limit of 1.2 A. The high-side on-resistance is a typical 450 mΩ and the low-side is 400 mΩ. Line regulation is a typical 0.2%.
The no-load quiescent is 27 µA making for some good efficiencies, which depend on the input voltage and how close it is to the output voltage, of course. Efficiencies peak at just about 100 mA and with a 2.5-V output (using a 6.8 µH switch inductor), for example, they range from 97% with 2.7-V input down to 92% with a 5-V input.
The performace of each of the channels in the dual AAT2512 is identical to that in the AAT1146. There is both over-temperature and current-limit protection in the devices. Recommended input and output capacitors are X5R or X7R ceramics from 4.7 µF to 10 µF with switch inductor values ranging from 2.2 µH to 6.8 µH (with increasing output voltage).
Although the complete news release and the company's web site mention fixed voltage versions of these parts there is no information about them in the data sheet and about voltages will be offered.
These parts are well worth looking at for any portable/handheld application where transient speed is important. They are priced to get attention.
The AAT1146 is in production in Pb-free SC-70-8 priced at $0.87 in 1000-piece lots, while the AAT2512 is in production in Pb-free TDFN-12 priced at $1.64, also in 1000-piece lots.
Data Sheet AAT2512
Data Sheet AAT1146