LTC3589 datasheet(20/38 Pages) LINER

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LTC3676/LTC3676-1

3676ff

For more information www.linear.com/LTC3676

operaTion

Table 8. Buck1, Buck2, Buck3, and Buck4 Slewing DAC Control

Command Registers

COMMAND

VALUE SETTING

DVB1A[4:0]

bbbbb Buck1 Reference DAC Input A

DVB1A[5]

Select DVB1A[4:0]

Select DVB1B[4:0]

DVB1B[4:0]

bbbbb Buck1 Reference DAC Input B

DVB1B[5]

Pull PGOOD Low Slewing Buck1

Do Not Pull PGOOD Slewing Buck1

DVB2A[4:0]

bbbbb Buck2 Reference DAC Input A

DVB2A[5]

Select DVB2A[4:0]

Select DVB2B[4:0]

DVB2B[4:0]

bbbbb Buck2 Reference DAC Input B

DVB2B[5]

Pull PGOOD Low Slewing Buck2

Do Not Pull PGOOD Slewing Buck2

DVB3A[4:0]

bbbbb Buck3 Reference DAC Input A

DVB3A[5]

Select DVB3A[4:0]

Select DVB3B[4:0]

DVB3B[4:0]

bbbbb Buck3 Reference DAC Input B

DVB3B[5]

Pull PGOOD Low Slewing Buck3

Do Not Pull PGOOD Slewing Buck3

DVB4A[4:0]

bbbbb Buck4 Reference DAC Input A

DVB4A[5]

Select DVB4A[4:0]

Select DVB4B[4:0]

DVB4B[4:0]

bbbbb Buck4 Reference DAC Input B

DVB4B[5]

Pull PGOOD Low Slewing Buck4

Do Not Pull PGOOD Slewing Buck4

*denotes default power-on value.

PUSHBUTTON OPERATION

Operating Mode State Diagram

Figure 6 shows the state diagram of the LTC3676 enable

and sequence controller. First application of power to

VIN pin brings the controller to the power-on reset/hard

reset (POR/HRST) state. In this state the I2C command

registers have been set to their default values, only LDO1

is operating, and the device is waiting for pushbutton or

PWR_ON inputs. Regulator enable pins and command

POR/HRST state VIN draws typically 12µA.

Power Up Using Pushbutton

When the ON pin is held low for 400ms the WAKE pin is

pulledhigh,enablepinsarerecognized,andthefivesecond

PWR_ON timer is started. If in the ON state and PWR_ON

is low or a fault is detected, then WAKE is brought low and

after a 1 second power-down time, the STANDBY state

is entered. In STANDBY, the enable bits in the command

registers are cleared and enable pins are ignored. Table 9

shows the control of command registers, enables, and

WAKE at each state.

The 5 second power-on state is intended for the system to

detectthatpowerrailsarecorrectandeitherdrivePWR_ON

pin high or set command register bit CNTRL[7] high to

keep the rails active. If there were a system level problem

Figure 6. LTC3676 Operating Mode State Diagram

ENABLE

ALLOWED AND

WAKE HIGH

ENABLE

INHIBITED AND

WAKE LOW

POR/HRST

VIN HIGH

ON 400ms

OR PWR_ON

ON 10 SEC

OR I2C HRST

ON 400ms

OR PWR_ON

PWR_ON

OR FAULT

ON 10 SEC

OR I2C HRST

ON 10 SEC

OR I2C HRST

1 SEC OFF

TIMER

HRST

3676 F06

1 SEC OFF

TIMER

STANDBY

5 SEC

PWR_ON

TIMER

STANDBY

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