While other manufacturers are busy putting op. amps., DACs and the like into the tiny SC-70 package, Micrel is able to crow about squeezing a respectably-performing 80-mA LDO in there. Indeed, many offerings from others are only now just beginning to hit the market in SOT-23. With the SC-70 package occupying only about 40% of the board area taken by a SOT-23, the space savings are considerable if they can be fully taken advantage of; Micrel has reinforced the savings with a stable LDO design that requires a much smaller output capacitor than normally expected.

The OEM approach to power distribution in portable products is deeply divided by those who want a centralized regulator for the complete product and those who want really local control of regulation. The latter viewpoint results in designs that "sprinkle" LDOs around the product, maybe up to six parts in some cellular phones, with the regulators ending up physically close to their respective load: the supporters of this approach believe that the better control and lower crosstalk that result are worth the extra parts. These are the users that Micrel is targeting with the MIC5213.

Performance is similar to the already-released MIC5203 (in SOT-23) and no premium is being charged for the smaller part; Micrel expects to see some of their present SOT-23 customers migrate to the smaller part as well as attracting a considerable number of new users. Initially the part is being produced at the standard 2.8, 3.0, 3.3 and 3.6-V levels while special-order voltages are available in the range from 2.8 to 4.0 V - in 100 mV increments. A 2.5-V part is in the immediate pipeline and 1.8-V parts are being closely looked at.

The typical dropout voltage of the MIC5213 is about 20 mV at light loads and 300 mV at the full 80-mA output, while the ground current is a low 225 m A at a 20-mA output.

With many LDO regulators it is not possible to keep the output stable and within regulated limits when there is no load. With the present trend to lower-and-lower sleep-mode currents it is becoming more and more important to have the LDO stable in such operating conditions. The MIC5213 is ultra-stable, requiring only a 0.47-m F output capacitor for each LDO output. This is not achieved with built-in series resistance but by slowing the transient response of the regulation loop. The enable characteristic of the 3.3-V part, for example, brings the output voltage to 100% in about 10 m s, an entirely acceptable time for the vast majority of portable applications.

In addition to the low value of the output capacitor, this part may also be a low-cost ceramic chip part; although a tantalum can be used, the filtering effects of the ceramic are better - against which the value-stability of the ceramic with temperature changes is poorer, changing the transient responses of the output somewhat.

The off-mode current of the part is immeasurably low. The current is specified simply as being below 10 pA, because of test limitations, but the device is totally internally unbiased when the enable voltage is held below 0.6 V. Pulling the enable input high (>2.0 V) allows operation to re-start. The enable input draws a small amount of current in the "high" position, typically 15 m A, but while the logic is TTL/CMOS compatible the enable input can be taken as high as 20 V without damage. ESD protection on the enable pin is 500 V while it is 2 kV on the other pins of the part.

The feature set of the MIC5213 is completed with current limiting, reversed-supply (reversed battery) polarity protection, and over-temperature shutdown.

Expect to see a number of quick design wins for this part in cellular phones, notebook and palmtop computers, and other battery-powered portables - particularly pagers. As the first LDO in SC-70 it will be an extremely profitable part for Micrel, even at $0.50 in 1000-piece lots. Samples are available now with deliveries starting in the second quarter of 1999.