SMM205
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
STATUS REGISTER
A status register exists for I2C polling of the status of
the COMP1 and COMP2 inputs. Two bits in this
status register reflect the current state of the inputs (1
= fault, 0 = no fault). Two additional bits show the
state of the inputs latched by one of two events
programmed in the configuration. The first event
option is the FAULT# output going active. The second
event option is the READY pin going low. The READY
pin is an I/O. As an output the READY output pin
goes active when the DC controlled voltages are at
their set point. As an input programmed to active high
it can be pulled low externally and latch the state of
the COMP inputs. This second event option allows
the state of the COMP inputs on multiple devices to be
latched at the same time while a host monitors their
FAULT# outputs.
The margin command registers contain two bits that
decode the commands to margin high, to margin low,
or to control to the nominal setting. Once the SMM205
receives the command to margin the supply voltage it
begins adjusting the supply voltage to move toward
the desired setting. When this voltage setting is
reached a bit is set in the margin status registers and
the READY signal becomes active.
Note: Configuration writes or reads of registers 00HEX
to 03HEX should not be performed while the SMM205 is
margining.
WRITE PROTECTION
Write protection for the SMM205 is located in a volatile
register where the power-on state is defaulted to write
protect. There are separate write protect modes for
the configuration registers and memory. In order to
remove write protection the code 55HEX is written to the
write protection register. Other codes will also enable
write protection. For example, writing 59HEX will allow
writes to the configuration register but not to the
memory, while writing 35HEX will allow writes to the
memory but not to the configuration registers. The
SMM205 also features a Write Protect pin (WP#)
which, when asserted, prevents writing to the
configuration registers and EE memory. In addition to
these two forms of write protection there is also a
configuration register lock bit which, once
programmed, does not allow the configuration
registers to be changed.
MARGINING
The SMM205 has two additional Active DC Output
Control voltage settings: margin high and margin low.
The margin high and margin low settings can be as
much as ±10% of the nominal setting depending on
the manufacturer. The SMM205 range can be as
large as VREF_CNTL to VDD. These settings are
stored in the configuration registers and are loaded
into the Active DC Output Control voltage setting by
margin commands issued via the I2C bus. The device
must be enabled for Active DC Output Control in order
to enable margining.
Figure 5 – SMM205 margin example. The nominal setting for channel 1 and 2 is 2.5V and 1.8V. The device
margins the DC/DC converters from nominal to high (2.8V and 2.1) then to nominal, then to low (2.3V and
1.5V), then to nominal, then to channel 1 high and channel 2 low, and then back to nominal. The READY
signals goes low when margining and high when complete.
Summit Microelectronics, Inc
2069 1.4 6/23/03
9
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
