SMM764
Preliminary Information
APPLICATIONS INFORMATION
DEVICE OPERATION
POWER SUPPLY
ADOC and force-shutdown, which can be used during
monitoring and margining mode. A detailed description
of each mode and feature follows.
The SMM764 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 SMM764.
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. When
multiple Sequence-Link™ devices are connected, the
same VDD and/or 12VIN supplies must power all
devices.
ACTIVE DC OUTPUT CONTROL (ADOCTM)
The SMM764 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 SMM764 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”, “FB”, or “Sense” node in a user’s custom
circuit, Figure 13. Each of the TRIMX pins on the
SMM764 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 4
channels (A-D) every 1.7ms making slight adjustments
to the voltage on the associated TRIMX output pins
based on the voltage inputs on the VMX pins. These
voltage adjustments allow the SMM764 to control the
output voltage of power supply converters to within
±0.2% when using a ±0.1% external voltage reference.
MODES OF OPERATION
The SMM764 has four basic modes of operation
(shown in Figures 5 through 8): power-on sequencing
mode, ongoing operations-monitoring mode, supply
margining mode, and power-on sequencing mode. In
addition, there are two features:
Figure 7 - Waveform shows four SMM764 channels Figure 8 - Waveform shows three SMM764 channels
exhibiting Sequence-on to Nominal voltage, Margin Sequencing-on to Nominal voltage, Margin High and
High or Low, Nominal voltage and then sequence-off
Ch 1 = 3.3V DC-DC converter output (Yellow trace)
Ch 2 = 2.5V DC-DC converter output (Blue trace)
Ch 3 = 2.0V DC-DC converter output (Purple trace)
Ch 4 = 1.8V DC-DC converter output (Green trace)
Low, and then sequence-off. Channel 4 shows the
HEALTHY signal.
Ch 1 = 3.3V DC-DC converter output (Yellow trace)
Ch 2 = 2.5V DC-DC converter output (Blue trace)
Ch 2 = 2.0V DC-DC converter output (Purple trace)
Ch 4 = Healthy signal output (Green trace)
Summit Microelectronics, Inc
2098 1.1 6/29/2005
14
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
