SMM465
Preliminary Information
APPLICATIONS INFORMATION
monitoring and margining mode. A detailed description
of each mode and feature follows.
DEVICE OPERATION
POWER SUPPLY
ACTIVE DC OUTPUT CONTROL (ADOCTM)
The SMM465 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 SMM465.
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.
The SMM465 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 SMM465 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 TRIMX pins on the SMM465 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 four 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 SMM465 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 SMM465 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
Figure 7 - Waveform shows four SMM465 channels Figure 8 - Waveform shows two SMM465 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
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 = 1.8V 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
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
Summit Microelectronics, Inc
2085 1.1 05/27/04
13
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
