SMM105
Preliminary Information
APPLICATIONS INFORMATION
DEVICE OPERATION
POWER SUPPLY
The SMM105 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 (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 SMM105. 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 SMM105 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 SMM105 has two basic modes of operation: UV
and OV monitoring mode and supply margining mode
,and one key feature, Active DC Output Control
(ADOC
TM
). A detailed description of each mode and
feature follows.
ACTIVE DC OUTPUT CONTROL (ADOC
TM
)
The SMM105 can control the DC output voltage of
bricks or DC/DC converters that have a trim pin. The
TRIM pin on the SMM105 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 SMM105 to
control the output voltage of the power supply
converter to within ±0.2% when using a ±0.1%
external voltage reference.
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 device can be programmed to either enable or
disable the ADOC function. When disabled or not
active, the TRIM pin on the SMM105 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 SMM105 controlling
that voltage to the ADOC nominal setting.
There are programmable Start times, T
START
, which are
used to delay the ADOC function to allow the
controlled supply to turn fully on before changing the
output voltage level. There is also a programmable
Speed-Up Convergence option.
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.
MONITORING
The SMM105 monitors the COMP1 and COMP2
inputs as well as the VM pin. COMP1 and COMP2
are high impedance inputs, each connected internally
to a comparator and compared against the
VREF_CNTL input.
Each comparator can be
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 SMM105 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 margining mode.
Summit Microelectronics, Inc
2068 1.8 09/20/05
8
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
