LTC3589-1 datasheet(16/38 Pages) LINER

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LTC3676/LTC3676-1

3676ff

For more information www.linear.com/LTC3676

Figure 2. LDO1, LDO2 and LDO4 Application Circuit

operaTion

LTC3676 Resistor Programmable LDO2 and LDO4

LDO2andLDO4outputvoltagesareprogrammedbyresis-

tor dividers tied from the LDO output pin to the feedback

pin as shown in Figure 2. The output voltage is calculated

using the following formula:

VLDO = 725• 1+

⎛

⎝⎜

⎞

⎠⎟

( )

output is 1.2V with selectable outputs of 2.5V, 2.8V, and

3.0V. LDO4 is enabled only through the command register

bit LDOB[2].

LDO4 Command Register Controls

Table 3. LDO4 Control Command Register Settings

COMMAND

LDOB[0]

Do Not Keep Alive LDO4 in Standby

Keep Alive LDO4 in Standby

LDOB[1]

Enable LDO4 at Any Output Voltage

Enable LDO4 Only if Output Voltage is <300mV

LDOB[2]

(LTC3676)

LDO4 Disabled if EN_L4 is Low

LDO4 Enabled

LDOB[2]

(LTC3676-1)

LDO4 Disabled

LDO4 Enabled

LDOB[4:3]

(LTC3676-1)

00* LDO4 Output = 1.2V

LDOB[4:3]

(LTC3676-1)

LDO4 Output = 2.5V

LDOB[4:3]

(LTC3676-1)

LDO4 Output = 2.8V

LDOB[4:3]

(LTC3676-1)

LDO4 Output = 3V

*denotes default power-on value.

STEP-DOWN SWITCHING REGULATORS

The LTC3676 contains four buck regulators. Two of the

buck regulators are capable of delivering up to 2.5A load

current and the other two can deliver up to 1.5A each. The

regulators have forward and reverse current limiting, soft-

start, and switch slew rate control for lower radiated EMI.

The LTC3676 buck regulators are capable of 100% duty

cycle,ordropout,regulation.Whenindropouttheregulator

outputvoltageisequaltoPVINminustheloadcurrenttimes

RDS(ON)oftheconvertersPMOSdeviceandinductorDCR.

Each buck regulator is enabled using its enable pin or I2C

command register control. Operating modes, start-up op-

tion, reference voltage, and switch slew rate are controlled

using the I2C port.

The buck converter I2C command register controls are

shown in Table 4, Table 5, Table 6, and Table 7.

–

VIN

LDO

3676 F02

1µF

0.725V

Fixed Output LDO3

Regulator LDO3 has a fixed voltage output of 1.8V.

Table 2. LDO2 and LDO3 Control Command Register Settings

COMMAND

LDOA[0]

Do Not Keep Alive LDO2 in Standby

Keep Alive LDO2 in Standby

LDOA[1]

Enable LDO2 at Any Output Voltage

Enable LDO2 Only if Output Voltage is <300mV

LDOA[2]

LDO2 Disabled if EN_L2 is Low

LDO2 Enable

LDOA[3]

Do Not Keep Alive LDO3 in Standby

Keep Alive LDO3 in Standby

LDOA[4]

Enable LDO3 at Any Output Voltage

Enable LDO3 0nly if Output Voltage is <300mV

LDOA[5]

LDO3 Disabled if EN_L3 is Low

LDO3 Enabled

*denotes default power-on value.

LDO4 Operation LTC3676-1

LDO4 on the LTC3676-1 has neither enable nor feedback

pins. There are four LDO4 output voltages selectable by

command register bits LDOB[4:3]. The power-on default

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