LP3921

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SNVS580A – AUGUST 2008 – REVISED MAY 2013

REGULATORS

Seven low-dropout linear regulators provide programmable voltage outputs with current capabilities of 80 mA,

150 mA and 300 mA as given in the table below. LDO1, LDO2 and LDO3 are powered up by default with LDO1

reaching regulation before LDO2 and LDO3 are started. LDO1, LDO3 and LDO7 can be disabled/enabled via the

serial interface. LDO1 and LDO2, if enabled, must be in regulation for the device to power up and remain

powered. LDO4, LDO5 and LDO6 have external enable pins and may power up following LDO2 as determined

by their respective enable. Under voltage lockout oversees device start up with preset level of 2.85V (typ.).

POWER SUPPLY CONFIGURATIONS

At PMU start up, LDO1, LDO2 and LDO3 are always started with their default voltages. The start up sequence of

the LDO's is given below.

Startup Sequence

LDO1 -> LDO2 -> LDO3

LDO's with external enable control (LDO4, LDO5, LDO6) start immediately after LDO2 if enabled by logic high at

their respective control inputs.

LDO7 (and LDO1, LDO3) may be programmed to enable/disable once PS_HOLD has been asserted.

DEVICE PROGRAMMABILITY

An I2C compatible Serial Interface is used to communicate with the device to program a series of registers and

also to read status registers. These internal registers allow control over LDO outputs and their levels. The

charger functions may also be programmed to alter termination voltage, end of charge current, charger restart

voltage, full rate charge current, and also the charging mode.

This device internal logic is powered from LDO2.

Table 1. LDO Default Voltages

LDO

Function

mA

Default Voltage (V)

Startup Default

Enable Control

1

CORE

300

1.8

ON

SI

2

DIGI

300

3.0

ON

-

3

ANA

80

3.0

ON

SI

4

TCXO

80

3.0

OFF

TCXO_EN

5

RX

150

3.0

OFF

RX_EN

6

TX

150

3.0

OFF

TX_EN

7

GP

150

3.0

OFF

SI

Table 2. LDO Output Voltages Selectable via Serial Interface

LDO

mA

1.5

1.8

1.85

2.5

2.6

2.7

2.75

2.8

2.85

2.9

2.95

3.0

3.05

3.1

3.2

3.3

1

CORE

300

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

2

DIGI

300

+

+

+

+

+

+

+

+

+

+

+

+

+

3

ANA

80

+

+

+

+

+

+

+

+

4

TCXO

80

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

5

RX

150

+

+

+

+

+

+

+

+

6

TX

150

+

+

+

+

+

+

+

+

7

GP

150

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

LP3921 Pin Descriptions(1)

Pin#

Name

Type(1)

Description

1

LDO6

A

LDO6 Output (TX)

2

TX_EN

DI

Enable control for LDO6 (TX). HIGH = Enable, LOW = Disable

3

LDO5

A

A LDO5 Output (RX)

(1)

Key: A=Analog; D=Digital; I=Input; DI/O=Digital-Input/Output; G=Ground; O=Output; P=Power

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