LP3918

SNVS476D – AUGUST 2007 – REVISED MAY 2013

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INPUT VOLTAGES

There are two input voltage pins used to power the 7LDO's on the LP3918. VIN2is the supply for LDO3, LDO4,

LDO5, LDO6 and LDO7. VIN1is the supply for LDO1 and LDO2. These input voltages should be tied to the Batt

pin in the application.

PROGRAMMING INFORMATION

Enable via Serial Interface

Table 17. Register Address 8h'00: OP_EN

BIT

NAME

FUNCTION

0

LDO1_EN

Bit set to '0' - LDO disabled

Bit set to '1' - LDO enabled

2

LDO3_EN

3

LDO7_EN

Note that the default setting for this Register is [0000 0101]. This shows that LDO1 and 3 are enabled by default

whereas LDO7 is not enabled by default on start up.

LDO OUTPUT PROGRAMMING

Table 18.

Register

NAME

Data Range (hex)(1)

Output Voltage

Add (hex)

01

LDO1PGM

03 - 0F

1.5V to 3.3V

O/P

(def. 1.8V)

02

LDO2PGM

00 - 0F

2.5V to 3.3V

O/P

(def 3.0V)

03

LDO3PGM

05 - 0C

2.7V to 3.05V

O/P

(def 3.0V)

04

LDO4PGM

00 - 0F

1.5V to 3.3V

O/P

(def 3.0V)

05

LDO5PGM

05 - 0C

2.7V to 3.05V

O/P

(def 3.0V)

06

LDO6PGM

05 - 0C

2.7V to 3.05V

O/P

(def 3.0V)

07

LDO7PGM

00 - 0F

1.5V to 3.3V

O/P

(def 3.0V)

(1)

See Table 2 for full programmable range of values.

EXTERNAL CAPACITORS

The Low Drop Out Linear Voltage regulators on the LP3918 require external capacitors to ensure stable outputs.

The LDO's on the LP3918 are specifically designed to use small surface mount ceramic capacitors which require

minimum board space. These capacitors must be correctly selected for good performance

INPUT CAPACITOR

Input capacitors are required for correct operation. It is recommended that a 10µF capacitor be connected

between each of the voltage input pins and ground (this capacitance value 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 analogue

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 failures 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 specified by the manufacturer to have surge current rating sufficent for the application. There are no

requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and temperature

coefficient must be considered when selecting the capacitor to ensure the capacitance will remain within its

operational range over the entire operating temperature range and conditions.

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