LP3921

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SNVS580A – AUGUST 2008 – REVISED MAY 2013

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 LDO3 are enabled by

default whereas LDO7 is not enabled by default on start up.

Table 18. LDO Output Programming(1)

Register Add (hex)

Name

Data Range (hex)

Output Voltage

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 4 for full programmable range of values.

EXTERNAL CAPACITORS

The Low Drop Out Linear Voltage regulators on the LP3921 require external capacitors to ensure stable outputs.

The LDO's on the LP3921 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 10 µF 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 1 cm 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.

WARNING

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

guaranteed by the manufacturer to have surge current rating sufficient 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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