SMM205
Preliminary Information
APPLICATIONS INFORMATION
DEVICE OPERATION
POWER SUPPLY
The voltage on the TRIM_CAP pins is buffered and
applied to the TRIM pin. The voltage adjustments on
the TRIM pin 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 capacitor and the trim
gain of the converter. Calculation of the TRIM_CAP
capacitor to achieve a desired minimum ripple is
detailed in Application Note 37.
The SMM205 can be powered by either an 8V to 15V
input through the 12VIN pin or by a 2.7V to 5.5V input
through the VDD pin. 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 SMM205. 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.
The device can be programmed to either enable or
disable the Active DC Control function.
When
disabled or not active the TRIM pin on the SMM205 is
a high impedance input. The voltage on the TRIM pin
is buffered and applied to the TRIM_CAP pin charging
the capacitor. This allows a smooth transition from the
converter’s nominal voltage to the SMM205 controlling
that voltage to the Active DC Control nominal setting.
VOLTAGE REFERENCE
The SMM205 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.
There is a programmable Speed-Up 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.
MODES OF OPERATION
MONITORING
The SMM205 has one key feature: Active DC Output
Control (ADOC), and two basic modes of operation:
UV/OV monitoring mode and supply margining mode.
A detailed description of each feature and mode
follows.
The SMM205 monitors the COMP1 and COMP2
inputs as well as the VM pins. COMP1 and COMP2
are high impedance inputs, each connected internally
to
a
comparator and compared against the
VREF_CNTL input.
Each comparator can be
ACTIVE DC OUTPUT CONTROL (ADOC)
independently programmed to monitor for either UV or
OV. The monitor level is set externally with a resistive
voltage divider. The part can be programmed to
trigger the FAULT# pin when either COMPx
comparator has exceeded the UV or OV range. The
READY and FAULT# outputs of the SMM205 are
active as long as the triggering limit remains in a fault
condition. The READY pin is programmable active
high/low open drain output indicates that VM is at its
set point. When programmed as an active high output
READY can also be used as an input. When pulled
low it will latch the state of the comparator inputs.
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 while the device is in margining mode.
The SMM205 can control the DC output voltage of
bricks or DC/DC converters that have a trim pin. The
TRIM pin on the SMM205 is connected to the trim
input pin on the power supply converter. A sense line
from the channel’s point-of-load connects to the VM
input. The Active DC Control function cycles every
1.7ms making slight adjustments to the voltage on the
TRIM output pin based on the voltage input on the VM
pin. This voltage adjustment allows the SMM205 to
control the output voltage of the power supply
converter to within ±0.2% when using a ±0.1%
external voltage reference.
Summit Microelectronics, Inc
2069 1.4 6/23/03
8
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
