LP3985IM5-3.3 National Semiconductor, LP3985IM5-3.3 Datasheet - Page 13

• Manufacturer Part Number: LP3985IM5-3.3
• Description: IC, LDO VOLT REG, 3.3V, 150mA, 5-SOT-23
• Manufacturer: National Semiconductor

Specifications of LP3985IM5-3.3

• Primary Input Voltage: 6V
• Output Voltage Fixed: 3.3V
• Dropout Voltage Vdo: 100mV
• No. Of Pins: 5
• Output Current: 150mA
• Operating Temperature Range: -40°C To +125°C
• Termination Type: SMD
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Typical Performance Characteristics
C
Application Hints
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP3985 requires external
capacitors for regulator stability. The LP3985 is specifically
designed for portable applications requiring minimum board
space and smallest components. These capacitors must be
correctly selected for good performance.
INPUT CAPACITOR
An input capacitance of ) 1µF is required between the
LP3985 input pin and ground (the amount of the capacitance
may be increased without limit).
This capacitor must be located a distance of not more than
1cm from the input pin and returned to a clean analog
ground. A ceramic capacitor is recommended although a
good quality tantalum or film capacitor may be used at the
input.
Important: Tantalum capacitors can suffer catastrophic fail-
ures due to surge current when connected to a low-
impedance source of power (like a battery or a very large
capacitor). If a tantalum capacitor is used at the input, it must
be guaranteed by the manufacturer to have a surge current
rating sufficient for the application.
There are no requirements for the ESR on the input capaci-
tor, but tolerance and temperature coefficient must be con-
sidered when selecting the capacitor to ensure the capaci-
tance will remain within the operational range over the full
range of temperature and operating conditions.
OUTPUT CAPACITOR
Correct selection of the output capacitor is important to
ensure stable operation in the intended application.
The output capacitor must meet all the requirements speci-
fied in the recommended capacitor table over all conditions
in the application. These conditions include DC-bias, fre-
quency and temperature. Unstable operation will result if the
capacitance drops below the minimum specified value. (See
the next section Capacitor Characteristics).
The LP3985 is designed specifically to work with very small
ceramic output capacitors. A 1.0µF ceramic capacitor (dia-
lectric type X7R) with ESR between 5mΩ to 500mΩ is
suitable in the LP3985 application circuit. X5R capacitors
BYPASS
= 0.01 µF, V
Output Impedance (V
IN
= V
OUT
+ 0.2V, T
IN
= 4.2V)
A
= 25˚C, Enable pin is tied to V
10136465
Unless otherwise specified, C
13
may be used but have a narrower temperature range. With
these and other capacitor types (Y5V, Z6U) that may be
used, selection is dependant on the range of operating con-
ditions and temperature range for that application. (see sec-
tion on Capacitor Characteristics).
It may also be possible to use tantalum or film capacitors at
the output, but these are not as attractive for reasons of size
and cost (see next section Capacitor Characteristics).
It is also recommended that the output capacitor be placed
within 1cm from the output pin and returned to a clean
ground line.
CAPACITOR CHARACTERISTICS
The LP3985 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 1µF to 4.7µF range,
ceramic capacitors are the smallest, least expensive and
have the lowest ESR values (which makes them best for
eliminating high frequency noise). The ESR of a typical 1µF
ceramic capacitor is in the range of 20 mΩ to 40 mΩ, which
easily meets the ESR requirement for stability by the
LP3985.
For both input and output capacitors careful interpretation of
the capacitor specification is required to ensure correct de-
vice operation. The capacitor value can change greatly de-
pendant on the conditions of operation and capacitor type.
In particular the output capacitor selection should take ac-
count of all the capacitor parameters to ensure that the
specification is met within the application. Capacitance value
can vary with DC bias conditions as well as temperature and
frequency of operation. Capacitor values will also show
some decrease over time due to aging. The capacitor pa-
rameters are also dependant on the particular case size with
smaller sizes giving poorer performance figures in general.
As an example Figure 3 shows a typical graph showing a
comparison of capacitor case sizes in a Capacitance vs. DC
Bias plot. As shown in the graph, as a result of the DC Bias
condition the capacitance value may drop below the mini-
mum capacitance value given in the recommended capacitor
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
IN
. (Continued)
Output Impedance (V
IN
= C
OUT
IN
= V
= 1 µF Ceramic,
OUT
+ 0.2V)
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