Datasheet

LP5900
SNVS358O –JULY 2005–REVISED MAY 2013 www.ti.com
CAPACITOR CHARACTERISTICS
The LP5900 is designed to work with ceramic capacitors on the input and output to take advantage of the
benefits they offer. For capacitance values in the range of 0.47 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 0.47 μF ceramic capacitor is in the range of 20 mΩ to 40 mΩ, which easily meets the ESR
requirement for stability for the LP5900.
The temperature performance of ceramic capacitors varies by type and manufacturer. 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 0.47 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.
NO-LOAD STABILITY
The LP5900 will remain stable and in regulation with no external load.
ENABLE CONTROL
The LP5900 may be switched ON or OFF by a logic input at the ENABLE pin. A high voltage at this pin will turn
the device on. When the enable pin is low, the regulator output is off and the device typically consumes 3nA.
However if the application does not require the shutdown feature, the V
EN
pin can be tied to V
IN
to keep the
regulator output permanently on. In this case the supply voltage must be fully established 500 μs or less to
ensure correct operation of the startup circuit. Failure to comply with this condition may cause a delayed startup
time of several seconds.
A 1MΩ pulldown resistor ties the V
EN
input to ground, this ensures that the device will remain off when the
enable pin is left open circuit. To ensure proper operation, the signal source used to drive the V
EN
input must be
able to swing above and below the specified turn-on/off voltage thresholds listed in the Electrical Characteristics
section under V
IL
and V
IH
.
DSBGA MOUNTING
The DSBGA package requires specific mounting techniques, which are detailed in Texas Instruments Application
Note AN-1112, SNVS009.
For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the
micro SMD device.
DSBGA LIGHT SENSITIVITY
Exposing the DSBGA device to direct light may cause incorrect operation of the device. Light sources such as
halogen lamps can affect electrical performance if they are situated in proximity to the device.
Light with wavelengths in the red and infra-red part of the spectrum has the most detrimental effect; thus, the
fluorescent lighting used inside most buildings has very little effect on performance.
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