Datasheet

0 1.0
2.0
_
3.0
_
4.0
_
5.0
_
CAP VALUE (% OF NOM. 1 uF)
DC BIAS (V)
100%
80%
60%
40%_
20%
_
0402, 6.3V, X5R
0603, 10V, X5R
LP3990
www.ti.com SNVS251I –MAY 2004–REVISED MAY 2013
in the capacitance value falling below the minimum value given in the recommended capacitor specifications
table (0.7µF in this case). Note that the graph shows the capacitance out of spec for the 0402 case size
capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers’ specifications for
the nominal value capacitor are consulted for all conditions, as some capacitor sizes (e.g. 0402) may not be
suitable in the actual application.
Figure 1. Graph Showing a Typical Variation in Capacitance vs DC Bias
The ceramic capacitor’s capacitance can vary with temperature. The capacitor type X7R, which operates over a
temperature range of -55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R
has a similar tolerance over a reduced temperature range of -55°C to +85°C. Many large value ceramic
capacitors, larger than 1µF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance
can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore X7R is recommended over
Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C.
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 0.47µF to 4.7µF 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.
ENABLE CONTROL
The LP3990 features an active high Enable pin, V
EN
, which turns the device on when pulled high. When not
enabled the regulator output is off and the device typically consumes 2nA.
If the application does not require the Enable switching feature, the V
EN
pin should be tied to V
IN
to keep the
regulator output permanently on.
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 Application Note AN1112.
For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the
DSBGA device.
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