
SMM665B 
 Preliminary Information
Summit Microelectronics, Inc 
2089  1.1  10/20/04 
13 
 APPLICATIONS INFORMATION 
DEVICE OPERATION 
POWER SUPPLY 
The SMM665B can be powered by either a 12V input 
through the 12VIN pin or by a 3.3V or 5.0V input 
through the VDD pin.  The 12VIN pin feeds an internal 
programmable regulator that internally generates 
either 5.5V or 3.6V.  A voltage arbitration circuit allows 
the device to be powered by the highest voltage from 
either the regulator output or the VDD input.  This 
voltage arbitration circuit continuously checks for these 
voltages to determine which will power the SMM665B.  
The resultant internal power supply rail is connected to 
the VDD_CAP pin that allows both filtering and hold-
up of the internal power supply. To ensure that the 
input voltage is high enough for reliable operation, an 
under voltage lockout circuit holds the controlled 
supplies off until the UVLO thresholds are met.  
MODES OF OPERATION 
The SMM665B has four basic modes of operation 
(shown in Figures 5 through 8): Power-on cascade 
sequencing mode, ongoing operations-monitoring 
mode, supply margining mode and Power-off cascade 
sequencing mode.  In addition, there are two features: 
ADOC and forced shutdown which can be used during 
monitoring and margining mode. A detailed description 
of each mode and feature follows. 
ACTIVE DC OUTPUT CONTROL (ADOC
TM
) 
The SMM665B can actively control the DC output 
voltage of bricks or DC/DC converters that have a trim 
pin during monitoring and margining mode.  The 
converter may be an off-the shelf compact device, or 
may be a “roll your own” circuit on the application 
board. In either case, the SMM665B dramatically 
improves voltage accuracy (down to 0.2%) by 
implementing closed-loop ADOC active control. This 
utilizes the DC-DC’s “trim” pin as shown in Figure 12, 
or an equivalent output voltage feedback adjustment 
“VADJ” or “FB” node in a user’s custom circuit, Figure 
13. Each of the TRIM
X
 pins on the SMM665B is 
connected to the trim input pins on the power supply 
converters.  A sense line from the channel’s point-of-
load connects to the corresponding VM input.  The 
ADOC function cycles through all six channels (A-F) 
every 1.7ms making slight adjustments to the voltage 
on the associated TRIM
X
 output pins based on the 
voltage inputs on the VM
X
 pins.  These voltage 
adjustments allow the SMM665B to control the output 
voltage of power supply converters to within ±0.2% 
when using a ±0.1% external voltage reference.
Figure 7 - Waveform shows four SMM665B channels 
exhibiting Sequence-on to Nominal voltage, Margin 
High or Low, Nominal voltage and then sequence-off 
Ch 1 = 2.5V DC-DC converter output (Yellow trace) 
Ch 2 = 1.8V DC-DC converter output (Blue trace) 
Ch 3 = 1.5V DC-DC converter output (Purple trace) 
Ch 4 = 1.2V DC-DC converter output (Green trace 
Figure 8 - Waveform shows two SMM665B channels 
Sequencing-on to Nominal voltage, Margin High and 
Low, and then sequence-off.  Channel 3 and 4 shows 
the RST and HEALTHY signals. 
Ch 1 = 2.5V DC-DC converter output (Yellow trace) 
Ch 2 = 1.5V DC-DC converter output (Blue trace) 
Ch 3 = RST signal output (Purple trace) 
Ch 4 = HEALTHY signal output (Green trace