LTC3589_12 Datasheet, PDF (17/50 Pages) Linear Technology – 8-Output Regulator with Sequencing and I2C

LTC3589/LTC3589-1/
LTC3589-2
OPERATION
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, 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 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 1 second
Enable Delay
<2ms
<2ms
Buck2 Current
1A
Output
1.2A
1.2A
Buck3 Current
1A
Output
1.2A
1.2A
PGOOD Fault
Timeout
Enabled by
Default. I²C
Disable.
Disabled by
Default. I²C
Enable.
Disabled by
Default. I²C
Enable.
PWR_ON to WAKE 50ms
2ms
2ms
Delay
LDO3 V_OUT
LDO4 V_OUT
* Indicates Default
V_OUT
Default LDO4
Enable
1.8V
1.8V, 2.5V,
2.8V*, 3.3V
LDO34_EN Pin
2.8V
1.2V*, 1.8V,
2.5V, 3.2V
I²C
2.8V
1.2V*, 1.8V,
2.5V, 3.2V
I²C
Wait to Enable Until Yes by Default. Yes by Default. No by Default.
Output < 300mV I²C Select.
I²C Select.
I²C Select.
Insert 2k Discharge Yes if Start-Up Yes if Start-Up Always
Resistor When
is Wait to Enable is Wait to Enable
Disabled
Until Output < Until Output <
300mV
300mV
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
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