
SMM105 
 Preliminary Information 
Summit Microelectronics, Inc 
2068  1.8  09/20/05 
2 
GENERAL DESCRIPTION
The SMM105 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
TM
).  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 SMM105 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 the converter.  
Typical converters have 
±
2% accuracy ratings for their 
output voltage.  Using the Active DC Output Control 
feature of the SMM105 can increase the accuracy to 
±
0.1%.  This high accuracy control of the 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 can also be used for margining a 
supply during system test or may be turned off by de-
selecting the function in the Control Select Register.  
The margin high and margin low voltage settings can 
range from 0.3V to VDD around the converters’ 
nominal output voltage setting depending on the 
specified margin range of the DC-DC converter.  
When the SMM105 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 SMM105 
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 SMM105 can be 
powered from either a 12V or 8V input via an internal 
regulator or the VDD input (Figure 3).  
The SMM105 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 
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 SMM105 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. 
compared 
against 
the 
Figure 2 – Example Power Supply Margining using the SMM105.  The waveform on the left is margin low to
high from 1.6V to 2.0V and the waveform on the right is margin high to nominal from 2.0V to 1.8V.  The ADOC
function guarantees the output level to be within ±0.2% with a ±0.1% external reference.  The bottom
waveform is the READY signal indicating margin is complete.