SMD1108 Datasheet, PDF (24/29 Pages) Summit Microelectronics, Inc. – 8-Channel Auto-Monitor ADC In System Programmable Analog (ISPA) Device

SMD1108
Preliminary
APPLICATIONS INFORMATION
Overview
The SMD1108 Auto-Monitor ADC is designed to monitor
the environmental parameters on a telecommunications
line card or subsystem. Figure 9 shows the SMD1108
monitoring four dedicated supply lines — in this example:
5V, 3.3V 2.5V, and 1.8V — coming in Connector J16. For
each of these 4 channels there is an associated under-
voltage, over-voltage and over-current detection circuit.
These voltage and current inputs are connected internally
to an ‘Instant Action block’ (Figure 8), and, in the event of
a failure, can be programmed to log the fault in an internal
nonvolatile memory. The ability to log faults directly into
a nonvolatile status register allows systems designers
the ability to record data relating to system performance,
so that data about the environment is logged immediately
in the event of a failure on the subsystem. This provides
the ability to fault record — which can be critical when
trying to diagnose system faults — during reliability tests
or field failures. The SMD1108 also allows data to be
downloaded while still mounted on the line card. The
SMD1108 provides out-of-limit monitoring via four envi-
ronmental automonitor inputs (CH0 to CH3). Absolute
measurement of the parameters via an ADC allows
engineers to monitor the long term performance of the
subsystem to predict system failure allowing scheduled
maintenance to repair the problem before the failure
occurs. For example, a current increasing over a period
of months on an optical interface where a laser is aging,
or the DC output of a DC-DC Converter. There are four
general-purpose open collector outputs which can be
Current Flow
CHn
R_SENSE
OCn
Programmed
OC Thresholds
25mV, 50mV
Programmed
QuickTrip™ Thresholds
50mV, 75mV, 125mV
OC Signal
QuickTrip™
Programmed
UV Threshold
0.9V to 6.0V
Programmed
OV Offset
+120%/–244%
UV Signal
OV Signal
used to drive low current signals such as status LEDs.
They are all controlled via the serial data bus. Summit's
Windows-based Graphical User Interface (GUI) Pro-
gramming Software will allow the engineer to program the
SMD1108 via a host PC running Windows 9x, 2000 or NT.
The GUI is also available on the website at
www.summitmicro.com.
Power Supplies
The SMD1108 is designed to take power via the inputs
VCC0/Ch4 through VCC3/Ch7. These 4 inputs are inter-
nally diode-ORed. Consequently the highest supply
voltage actually supplies the current to the device. At
least one of these supplies must be above 2.7V for correct
device operation. Summit recommends 100nF decou-
pling capacitors across all voltage supply inputs. For
more information on these inputs see Figure 8, the Instant
Action Block. The AUXVCC signal is provided to create
a backup supply. This pin should have a 10µF capacitor
to ground, and should be isolated from the main supply.
AUXVCC is also used to power the part to access the
nonvolatile memory without having power applied to the
rest of the board. See recommended connections in the
Serial Interface section.
8 Channel 10 bit ADC
The SMD1108 can monitor system parameters and
measure each value to an absolute level. The analog
acquisition system consists of an 8-to-1 MUX, a 10-bit
ADC, voltage references, and the automonitor logic. The
ADC’s inputs are grouped into two banks of four. The CH0
to CH3 inputs are the primary environmental automonitor
channels, and the VCC0/Ch4 to VCC3/Ch7 inputs are the
supply monitors (see Figure 8). The interface to the ADC
is made via the two-wire serial data port. When the
SMD1108 is in automonitor mode (signal AUTOMON
high) the serial interface is disabled to prevent any noise
from the serial bus disturbing the ADC conversion. During
the development process the engineer can read the
values of the ADC channels directly using the Windows
GUI. The RDY# signal indicates when the ADC is busy
in conversion. There are three sources for the reference
voltage on the ADC. Two voltages are generated inter-
nally: 2.5V and 2.048V. These are doubled internally and
generate full scale values of 5V and 4.096V (or 4mV/bit),
respectively. In addition, it is possible to source the
reference voltage externally. These three options are
programmable through the GUI software.
2052 Fig08
Figure 8. Instant Action Block
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2052 2.0 10/05/01
SUMMIT MICROELECTRONICS, Inc.