SMS66
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
MONITORING
The SMS66 can be programmed to wait until either or
both VDD and 12VIN inputs are within their respective
voltage threshold limits before Power-on sequencing is
allowed to begin. This ensures that the converters
have their full supply voltage before they are enabled.
Once the Power-on sequence is complete and before
a Power-off sequence has been initiated, the SMS66
continues to monitor all VMX inputs, the VDD and
12VIN inputs, and two temperature sensor inputs with
a 10-bit ADC. Each of these inputs is sampled and
converted by the ADC every 2ms. The ADC input has
a range of 0V to four times the voltage on VREF_ADC
for inputs VMA-F and the VDD input. The range is
extended to 12 times VREF_ADC for the 12VIN input
and is reduced to two times VREF_ADC for the AIN1
Once Power-on sequencing begins, the SMS66 will
wait a Power-on delay time (tDPON) for any channel in
the first sequence position (0) and then activate the
PUPX outputs for those channels. The Power-on
delay times are individually programmable for each
channel. The SMS66 will then wait until all VMX inputs
of the channels assigned to the first sequence position
(0) are above their programmed UV1 thresholds. At
this point, the SMS66 will enter the second sequence
position (1) and begin to timeout the Power-on delay
times for the associated channels. This process
continues until all of channels in the sequence have
turned on and are above their UV1 threshold. The
status registers indicates that all sequenced power
supply channels have turned on.
The programmable sequence termination timer can be
used to protect against a stalled Power-on sequence.
This timer resets itself at the beginning of each
sequence position. All channels in the sequence
position must go above their UV1 threshold before the
sequence termination timer times out (tSTT) or the
sequence will terminate and all PUPX outputs will be
switched to their inactive state. The status registers
contain bits that indicate the sequence has been
terminated and in which sequence position the timer
timed out. This timer has four settings of OFF, 100ms,
200ms and 400ms.
and AIN2 inputs.
The SMS66 monitors internal
temperature using the 10-bit ADC and the automonitor
function. Two under temperature and two over
temperature thresholds can be set, each with its own
programmable trigger options and consecutive
conversion before trigger counter. Resolution is 0.25 C
per bit scaled over the range of -128 C to 127.75 C.
The temperature value can also be acquired over the
I2C bus as a 10-bit signed two's complement value.
The SMS66 compares each resulting ADC conversion
with two programmable 10-bit under-voltage limits
(UV1, UV2) and two programmable 10-bit over-voltage
limits (OV1, OV2) for the corresponding input.
A
consecutive conversion counter is used to provide
filtering of the ADC inputs. Each limit can be
programmed to require 1, 2, 4 or 6 consecutive out-of-
limit conversions before it is said to be in fault. One in-
limit conversion will remove the fault from the
threshold limit. This provides digital filtering of the
monitored inputs. The ADC inputs VMA-F can use
additional filtering by connecting a capacitor from the
corresponding CAPX pins to ground to form an analog
RC filter (R=25kΩ). The input is considered to be in a
fault condition if any of its limit thresholds are in fault.
Setting an OV threshold limit to full-scale (3FFHEX), or
setting an UV threshold limit to 000HEX ensures that
the limit can never be in fault. The status registers
provide the real-time status of all monitored inputs.
While the SMS66 is in the Power-on sequencing mode
the RST output is held active and the HEALTHY
output is held inactive regardless of trigger sources.
The Power-off and Force Shutdown trigger options are
also disabled while in this mode. Furthermore, the
SMS66 will not respond to activity on the
PWR_ON/OFF pin or to a Power-off I2C command
during Power-on sequencing mode.
The voltage threshold limits for inputs VMA-F, VDD and
12VIN can be programmed to trigger the RST and
HEALTHY outputs as well as a Force Shutdown and
Power-off operation when exceeded. The threshold
limits for the internal temperature sensor and the AIN1
and AIN2 inputs can be programmed to trigger the
RST, HEALTHY, and FAULT outputs.
Summit Microelectronics, Inc
2070 1.0 7/16/03
13
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
