MIC2827 Datasheet, PDF (13/27 Pages) Micrel Semiconductor – Triple Output PMIC with HyperLight Load™ DCDC, two LDOs, and I2C Control

Micrel, Inc.
Functional Description – Power Control
and Sequencing
Two Types of Part: Sequence-Enabled and No-
Sequence
• Sequence-Enabled parts support automatic
sequencing of the three supplies. Sequence-
Enabled parts all have a default sequence (activated
by asserting the EN pin). These parts also allow
sequencing to be disabled.
While very flexible, sequence-enabled parts require
more care in operation. See the later section
“Ensuring Clean Switching in Sequence-Enabled
Parts”.
• No-Sequence parts have no built-in sequencing
capability. Their default startup turns on only one
supply, which requires no sequencing. If the host
needs more supplies to come on, this can be
accomplished with I²C writes which allows a
sequence activated by software to be performed.
Power-up State
When battery power is first applied to the MIC2827, all
I²C registers are loaded with their default (POR) values.
If EN is high, a default startup is executed; otherwise,
the part remains in a quiescent state waiting to be
started by EN or an I²C command.
Enable Pin-Initiated Default Startup
When EN is asserted, a default startup is executed. This
is defined below:
• The voltage registers are loaded with their default
values.
• In sequence-enabled parts, the Sequence Control
bit is set to low (to allow sequencing to occur). No-
sequence parts always have zero for the Sequence
Control bit
• The correct set of supply enable bits is loaded into
the Enable Register, and the appropriate sequence
is then executed.
• The Power-On After Fault (POAF) bit is set to its
default state, high.
Turning on the Power Supplies
After power is applied, the MIC2827 offers two methods
of turning the three supply outputs on and off:
1. Default startup sequencing or shutdown via the
EN pin;
2. Flexible startup sequencing or shutdown via the
I²C interface
MIC2827
Power-Up via the EN Pin
The EN pin is transition sensitive and not level sensitive
(with the exception of hot enable—please see the
description below). If the EN pin is toggled low-to-high,
the MIC2827 will execute the default startup sequence.
During the startup sequence, the appropriate set of
supply enables is loaded into the Enable Register. This
allows the part to present a consistent interface to the
I²C host; if the host reads the Enable Control register, it
will see one or more enables on, which is consistent with
one or more active supplies.
Individual control of the supplies is now possible via the
I²C interface.
“Hot Enable” Startup
Some systems may choose to tie the EN pin to DVIN, so
that the MIC2827 registers an active EN pin as it
completes power-on. This is perfectly legal and
produces a default startup immediately after power is
applied. Depending on the rise time of the input power
being applied, the UVLO flag may be set.
Power-Down via the EN Pin
If the EN pin is toggled high-to-low, then the MIC2827
will shut down all outputs simultaneously. For reasons
similar to those above, at the conclusion of the shutdown
sequence, all three individual supply enables will be
clear in the Enable Control register and the bias will be
switched off.
If the MIC2827 startup is initiated by asserting EN and
later shutdown is initiated by clearing the Enable
Register bits, the part will be quiescent (with all bias
currents disabled) but EN will still be high. In this case,
de-asserting EN will have no effect, since the part has
already completed its shutdown.
Power-Up and Power-Down via the Enable Register
The three individual power supply enable bits in the
Enable Register (LDO2-EN, LDO1-EN, and DC-EN) may
be used to enable and disable individual supplies. If the
part is sequenced-enabled, and sequencing is permitted
by the Sequence Control bit, enabled supplies are
turned on in sequence. Any disabled outputs will not
participate in the sequence and will be ignored.
See also the “Ensuring Clean Switching in Sequence-
Enabled Parts” section.
Under no circumstances should the EN and I²C control
be used simultaneously. The results would not be
deterministic.
If a supply output is enabled and its Voltage Control
register is written with a new value, the output voltage
changes immediately at the I²C acknowledge.
July 2009
13
M9999-072709-A