LP3999

www.ti.com

SNVS207E – JUNE 2003 – REVISED MAY 2013

NO-LOAD STABILITY

The LP3999 will remain stable and in regulation with no external load. This is an important consideration in some

circuits, for example CMOS RAM keep-alive applications.

CAPACITOR CHARACTERISTICS

The LP3999 is designed to work with ceramic capacitors on the output to take advantage of the benefits they

offer. For capacitance values in the range of 1 µF to 4.7 µF, ceramic capacitors are the smallest, least expensive

and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a

typical 1 µF ceramic capacitor is in the range of 20 m

Ω to 40 mΩ, which easily meets the ESR requirement for

stability for the LP3999.

The temperature performance of ceramic capacitors varies by type. Most large value ceramic capacitors (

≥ 2.2

µF) are manufactured with Z5U or Y5V temperature characteristics, which results in the capacitance dropping by

more than 50% as the temperature goes from 25°C to 85°C.

A better choice for temperature coefficient in a ceramic capacitor is X7R. This type of capacitor is the most stable

and holds the capacitance within ±15% over the temperature range. Tantalum capacitors are less desirable than

ceramic for use as output capacitors because they are more expensive when comparing equivalent capacitance

and voltage ratings in the 1 µF to 4.7 µF range.

Another important consideration is that tantalum capacitors have higher ESR values than equivalent size

ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the

stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic

capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about

2:1 as the temperature goes from 25°C down to

−40°C, so some guard band must be allowed.

NOISE BYPASS CAPACITOR

the regulator output. This device pin connects directly to a high impedance node within the bandgap reference

circuitry. Any significant loading on this node will cause a change on the regulated output voltage. For this

reason, DC leakage current through this pin must be kept as low as possible for best output voltage accuracy.

The use of a 0.01µF bypass capacitor is strongly recommended to prevent overshoot on the output during start-

up.

The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High quality ceramic

capacitors with NPO or COG dielectric typically have very low leakage. Polypropolene and polycarbonate film

capacitors are available in small surface-mount packages and typically have extremely low leakage current.

Unlike many other LDO’s, the addition of a noise reduction capacitor does not effect the transient response of the

device.

ENABLE OPERATION

turn the device on. When the enable pin is low, the regulator output is off and the device typically consumes 3

be able to swing above and below the specified turn-on/off voltage thresholds listed in the Electrical

FAST TURN ON

Fast turn-on is ensured by control circuitry within the reference block allowing a very fast ramp of the output

voltage to reach the target voltage. There is no active turn-off on this device. Refer to LP3995 for a similar device

with active turn-off.

DSBGA MOUNTING

The DSBGA package requires specific mounting techniques which are detailed in TI's AN-1112 Application

Report (SNVA009).

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Product Folder Links: LP3999