LTC3589 datasheet(17/50 Pages) LINER

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LTC3589/LTC3589-1/

LTC3589-2

3589fe

The LTC3589 has ﬂexible options for enabling and sequenc-

ing the regulator enables. The regulators are enabled us-

ing input pins or the I2C serial port. To deﬁne a power-on

sequence tie the enable of the ﬁrst regulator to be powered

up to the WAKE pin. Connect the ﬁrst regulators output

to the enable pin of the second regulator, and so on. One

or more regulators may be started in any sequence. Each

enable pin has a 200μs (typical) delay between the pin

and the internal enable of the regulator. When the system

controllers are satisﬁed that power rails are up, the con-

troller must drive PWR_ON HIGH to keep WAKE active. To

ensure correct start-up sequencing, the regulators outputs

are monitored by voltage comparators which require each

output to discharge below 300mV before re-enabling. A

software control command register function is available

which sets the regulators to effectively ignore their enable

pins but respond to I2C register enables. This function

enables software-only control of any combination of pin-

strapped regulators and is useful for implementing system

power saving modes. Keep-alive mode exempts selected

regulators from turning off during normal shutdown. In

keep-alive mode, the LTC3589 powers down normally

and is ready for the next start-up sequence, but selected

regulators are kept on to power memory or other functions

during system standby modes.

The LTC3589 will shut down all regulators and pull down

the WAKE pin under high temperature, VIN undervoltage,

and extended low regulator output voltage conditions.

Status of a hard shutdown is reported by the IRQ status

pin and the IRQSTAT status register.

The I2C serial port on the LTC3589 contains 13 command

registers for controlling each of the regulators, one read-

only register for monitoring each regulators power good

status, one read-only register for reading the cause of

an IRQ event, and one clear IRQ command register. The

LTC3589 I2C supports random addressing of any register.

LTC3589, LTC3589-1, AND LTC3589-2 FUNCTIONAL

COMPARISON

Table 1. summarizes the functional differences between

the LTC3589, LTC3589-1, and LTC3589-2.

Table 1. LTC3589, LTC3589-1, and LTC3589-2 Functional

Differences

LTC3589

LTC3589-1

LTC3589-2

Power-On Inhibit

Enable Delay

1 second

<2ms

Buck2 Current

Output

1.2A

Buck3 Current

Output

1.2A

PGOOD Fault

Timeout

Enabled by

Default. I2C

Disable.

Disabled by

Default. I2C

Enable.

Disabled by

Default. I2C

Enable.

PWR_ON to WAKE

Delay

50ms

2ms

LDO3 VOUT

1.8V

2.8V

LDO4 VOUT

* Indicates Default

VOUT

1.8V, 2.5V,

2.8V*, 3.3V

1.2V*, 1.8V,

2.5V, 3.2V

1.2V*, 1.8V,

2.5V, 3.2V

Default LDO4

Enable

LDO34_EN Pin

I2CI2C

Wait to Enable Until

Output < 300mV

Yes by Default.

I2C Select.

Yes by Default.

I2C Select.

No by Default.

I2C Select.

Insert 2k Discharge

Resistor When

Disabled

Yes if Start-Up

is Wait to Enable

Until Output <

300mV

Yes if Start-Up

is Wait to Enable

Until Output <

300mV

Always

Details of the operation of the LTC3589 are found in the

following sections.

ALWAYS-ON LDO

The LTC3589 includes a low quiescent current low dropout

regulator that remains powered whenever a valid supply

is present on VIN. The always-on LDO will remain active

until VIN drops below 2.0V (typical). This is below the 2.5V

OPERATION

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