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lowpowerZONE Products for the week of August 25, 2008
Texas Instruments Says…
TPS62601: Thinnest 500-mA Power Converter Solution
6-MHz buck dc-dc converter supports ultra-thin, feature-rich smart phones, wireless modules and portable electronics
Giving portable designers the ability to add more features and functions on a handheld device, Texas Instruments Incorporated (TI) announced the industry’s smallest and thinnest 500-mA, step-down DC/DC converter solution for space-constrained applications. The high-efficiency power management integrated circuit (IC) is the first 6-MHz, 500-mA converter to achieve a 13-mm2 solution size with an ultra-thin 0.6-mm total height.
Leveraging TI’s analog manufacturing technology, the new TPS62601 converter achieves up to 89-percent power efficiency and only 30-uA typical operating quiescent current – all from a 0.9 mm x 1.3 mm chip scale package roughly the size of a flake of pepper. The synchronous, switch-mode device’s fixed frequency of 6 MHz allows the use of only one 0.47-uH inductor with a height of 0.6 mm and two low-cost ceramic capacitors, without compromising performance and efficiency.
“Portable system designers continue to desire more features on their devices, which require smaller, efficient DC/DC converters to maintain long battery life and system run-times,” said Steve Anderson, senior vice president of Power Management, TI. “The TPS62601 gives portable designers access to the smallest, thinnest 500-mA DC/DC solution, which simplifies design and reduces board space and time-to-market.”
EN-Genius Says…
The world of chip scale is throwing up some interesting thermal results and TI is taking advantage of them by making a fairly current “beefy” dc-dc buck converter in that format.
The TPS62600 and TPS62601 are nominal 6 MHz synchronous buck converters, each with a 2.3 V to 5.5 V input range. The output voltage of the TPS62600 is 1.83 V and that of the TPS62601 is 1.8 V. Both are rated at 500 mA maximum load.
The parts do not use a conventional feedback loop, using a non-linear switching of the p-channel and n-channel MOSFETs with virtually no delay in reacting to changes in the output voltage – giving a very high transient response. The potential divider for the feedback loop is on chip followed by a comparator but no high-gain loop amplifier. The block diagram suggests the reference for both parts is 0.8 V? This format also gives high stability over a range of switching inductor and output capacitor values. The intrinsic switching frequency of the converters is about 11 MHz, limited to 6 MHz by a frequency-controlled loop.
The parts change over to pulse skipping operation (PFM) at lower loads and the output voltage is positioned to about 0.5% above the nominal level to minimize the effects of any step load. The load current at which the switch to PFM takes place depends on the difference between the input and output voltages and is inversely proportional to both the switch inductor value and the operating frequency.
The quiescent current of the parts is a nominal 6.5 mA in PWM mode, dropping to 30 µA in PFM mode and 200 nA in shutdown mode. The efficiency varies with the difference between input and output voltages, of course: with the TPS62600 the efficiency peaks at about 90% (at 150 mA load) when the input is 2.7 V. This drops to about 87% (at 250 mA) when the input is 3.6 V. With the latter, however, the low load PFM mode keeps efficiency at better than 50% right down to 100 µA load. In forced PWM mode, by comparison, the efficiency is below 10% at 1 mA loading. TI is providing on their characteristic curves the power loss vs load curves that Linear has been using for some time.
The capacitors can be ceramic (with low ESR values) and values suggested as an initial start are 2.2 µF on the input and 4.7 µF on the output. The suggested inductance value is 0.47 µH with a quality factor higher than 25 required. Data Sheet assistance over component values and stability is very good.
There is undervoltage lockout at a 2.05 V threshold; thermal shutdown (140ºC junction temperature with 10ºC hysteresis); soft start (with duration depending on the load size, but with lower loads is 180 µs); anti-shoot through on the MOSFETs; current limit detection; and negative inductor current detection.
The p-channel MOSFET has an Rds(on) of 310 mΩ at 3.6 V and 380 mΩ at 2.5 V, with a maximum 1 µA leakage current. The n-channel MOSFET offers an Rds(on) of 250 mΩ at 3.6 V and 320 mΩ at 2.5 V, with a maximum leakage of 2 µA.
The dc output voltage regulation is ±1.5% in PWM operation and line regulation is a typical 0.25%/V.
TI has opted for a switching frequency that gives minimum component sizes, but that does have a bearing on efficiency, bringing it into the near 90% maximum mark rather than a bit over. The size and footprint of the surrounding components more than make up for that compromise. The nearest competition is probably the LM3691 which is in National’s MicroSMD (1.3mm x 1.6mm instead of TI’s 0.9mm x 1.3mm – a 43% real estate savings), although the National part is rated at 1 A and offers higher efficiencies (running at 4 MHz). These will be extremely high volume parts because of sizing and, unfortunately, because of the low price. They will be designed into a multitude of portable products that are using a secondary voltage rail, particularly phones and media players.
The TPS62600 and TPS62601 are in production in 6-bump chip scale (TI package YFF-6) priced at $1.45 in 1000-piece lots. An evaluation module is available.
Data Sheet
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