SMM605
Preliminary Information
APPLICATIONS INFORMATION
DEVICE OPERATION
POWER SUPPLY
The SMM605 can be powered by either an 6V to 14V
input through the 12VIN pin or by a 2.7V to 5.5V input
through the VDD pin (Figure 5). The 12VIN pin feeds
an internal programmable regulator that internally
generates either 5.5V or 3.6V. The internal regulator
must be set to 3.6V if using an 8V supply. 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 SMM605. 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.
VOLTAGE REFERENCE
The SMM605 can operate using either an internal or
external voltage reference, VREF. The internal VREF
is set to 1.25V. Total accuracy with a ±0.1% external
reference is ±0.2% and ±0.5% using the internal
reference.
MODES OF OPERATION
The SMM605 has two basic modes of operation:
supply margining mode and Active DC Output Control
(ADOC
TM
). A detailed description of each mode and
feature follows.
ACTIVE DC OUTPUT CONTROL (ADOC)
The SMM605 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 SMM605 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 7, or
an equivalent output voltage feedback adjustment
“VADJ” or “FB” node in a user’s custom circuit, Figure
8. Each of the TRIM
X
pins on the SMM605 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
X
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 SMM605 to control the output voltage of
power supply converters to within ±0.2% when using a
±0.1% external voltage reference.
The voltage on the TRIM_CAP
X
pins is buffered and
applied to the TRIM
X
pin. The voltage adjustments on
the TRIM
X
pins cause a slight ripple of less than 1mV
on the power supply voltage. The amplitude of this
ripple is a function of the TRIM_CAP
X
capacitor and
the trim gain of the converter. Calculation of the
TRIM_CAP
X
capacitor to achieve a desired minimum
ripple is detailed in Application Note 37.
The pulse of current can be increased to a 10X pulse
of current until the power supply voltages are at their
nominal settings by selecting the programmable Fast
Convergence option. As the name implies, this option
decreases the time required to bring a supply voltage
from the converter’s nominal output voltage to the
Active DC Output Control nominal voltage setting.
The device can be programmed to either enable or
disable the Active DC Control function.
When
disabled or not active, the TRIM
X
pins on the SMM605
are high impedance inputs. The voltage on the TRIM
X
pins are buffered and applied to the TRIM_CAP
X
pins
charging the capacitor.
This allows a smooth
transition from the converter’s nominal voltage to the
SMM605 controlling that voltage to the Active DC
Control nominal setting.
MONITORING
The SMM605 monitors the VM
X
pins. The READY pin
is programmable active high/low open drain output
indicates that all VM
X
pins are at their set point.
Summit Microelectronics, Inc
2064 1.1 09/16/03
9
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
