SMM205
Preliminary Information
Figure 2 – Example Power Supply Margining using the SMM205. The waveform on the left is margin nominal
to high from 2.5V to 2.8V and 1.8V to 2.1V. The waveform on the right is margin nominal to low from 2.5V to
2.2V and 1.8V to 1.5V. The bottom waveform is the READY signal indicating when margining is complete.
GENERAL DESCRIPTION
The SMM205 is capable of controlling and margining
the DC output voltage of LDOs or DC/DC converters
that use a trim/adjust pin and to automatically change
the level using a unique Active DC Output Control
(ADOC). The ADOC function is programmable over a
standard 2-wire I
2
C serial data interface and can be
used to set the nominal DC output voltage as well as
the margin high and low settings. The part actively
controls the programmed set levels to maintain tight
control over load variations and voltage drops at the
point of load. The margin range will vary depending on
the supply manufacturer and model but the normal
range is 10% adjustment around the nominal output
setting. However, the SMM205 has the capability to
margin from VREF_CNTL to VDD.
The user can set the desired voltage settings
(nominal, margin high and margin low) into the EE
memory array for the device. Then, volatile registers
are used to select one of these settings. The registers
are accessed over the I
2
C bus.
In normal operation, Active DC Output Control is set to
adjust the nominal output voltage of one or two
trimmed converters. Typical converters have
±2%
accuracy ratings for their output voltage. Using the
Active DC Output Control feature of the SMM205 can
increase the accuracy to
±0.2%.
This high accuracy
control of a converter output voltage is extremely
important in low voltage applications where deviations
in power supply voltage can result in lower system
performance. Active DC Output Control may be
turned off by de-selecting the function in the Control
Select Register. Active DC Output Control can also be
used for margining a supply during system test.
When the SMM205 receives the command to margin
the Active DC Output Control will adjust the supply to
the selected margin voltage. Once the supply has
reached its margined set point the Ready bit in the
status register will set and the READY pin will go
active. If Active DC Control is disabled a margined
supply can return to its nominal voltage by writing to
the margin command register.
In order to obtain maximum accuracy the SMM205
requires an external voltage reference. An external
reference with ±0.1% accuracy will enable an overall
±0.2% accuracy for the device. A configuration option
also exists so that an internal voltage reference can be
used, but with less accuracy. Total accuracy using the
internal reference is ±0.5%. The SMM205 can be
powered from either a 12V or 8V input via an internal
regulator, or the VDD input (Figure 3).
The SMM205 has two additional input pins and one
additional output pin. The input pins, COMP1 and
COMP2, are high impedance inputs, each connected
to a comparator and compared against the
VREF_CNTL input or the internal reference (VREF).
Each comparator can be independently programmed
to monitor for UV or OV. When either of the COMP1
or COMP2 inputs are in fault the open-drain FAULT#
output will be pulled low. A configuration option exists
to disable the FAULT# output during margining.
Programming of the SMM205 is performed over the
industry standard I
2
C 2-wire serial data interface. A
status register is available to read the state of the part,
and a Write Protect (WP#) pin is available to prevent
writing to the configuration registers and EE memory.
Summit Microelectronics, Inc
2069 1.4 6/23/03
2
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
