Datasheet

LTC3589/LTC3589-1/
LTC3589-2
17
3589ff
For more information www.linear.com/3589
The LTC3589 has flexible options for enabling and sequenc-
ing the regulator enables. The regulators are enabled us-
ing input pins or the I
2
C 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 I
2
C 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, V
IN
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 I
2
C 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 I
2
C 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 <2ms
Buck2 Current
Output
1A 1.2A 1.2A
Buck3 Current
Output
1A 1.2A 1.2A
PGOOD Fault
Timeout
Enabled by
Default. I
2
C
Disable.
Disabled by
Default. I
2
C
Enable.
Disabled by
Default. I
2
C
Enable.
PWR_ON to WAKE
Delay
50ms 2ms 2ms
LDO3 V
OUT
1.8V 2.8V 2.8V
LDO4 V
OUT
* Indicates Default
V
OUT
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 I
2
C I
2
C
Wait to Enable Until
Output < 300mV
Yes by Default.
I
2
C Select.
Yes by Default.
I
2
C Select.
No by Default.
I
2
C 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 V
IN
. The always-on LDO will remain active
until V
IN
drops below 2.0V (typical). This is below the 2.5V
operaTion