MIC2826 Datasheet, PDF (13/27 Pages) Micrel Semiconductor – Quad Output PMIC with HyperLight Load™ DCDC, three 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 four 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 MIC2826, 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 MIC2826 offers two methods
of turning the four 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
MIC2826
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 MIC2826 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 MIC2826 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, the MIC2826 will
shut down all outputs simultaneously. For reasons
similar to those above, at the conclusion of the shutdown
sequence, all four individual supply enables will be clear
in the Enable Control register and the bias will be
switched off.
If the MIC2826 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 four individual power supply enable bits in the
Enable Register (LDO3-EN, 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
M9999-071609-A