SMD1108 Datasheet, PDF (26/29 Pages) Summit Microelectronics, Inc. – 8-Channel Auto-Monitor ADC In System Programmable Analog (ISPA) Device

SMD1108
Preliminary
Temperature Sensor
The internal temperature sensor can be accessed as a
multiplexed optional input on CH3. Channel 3 can be set
to read an internal temperature dependant device with a
range of ±128ºC. The 10-bit ADC converts the tempera-
ture reading to data in 2’s complement format, and is
accurate to ¼ºC. The GUI software can enable the
Temperature Sensor and will change the displayed read-
ing on CH3 from volts to ºC.
Sense resistors
Care should be taken when designing the PCB layout for
the Sense resistors. A Kelvin, or 4 Wire, connection
scheme should be adopted as shown in Figure 10. Circuit
accuracy can be affected if the PCB trace to the resistor
is not optimized. Voltage drops across copper traces due
to current flow can cause additional errors.
High Current Path
Instant Action Block
A single channel of the Instant Action Block is shown in
Figure 8. The SMD1108 has a block of 12 nonvolatile
threshold comparators dedicated to monitoring the status
of the supply lines, they are arranged as:
Four Over-Voltage comparators,
Four Under-Voltage comparators, and
Four Over-Current comparators.
This structure has been adopted to ensure all supplies are
continuously monitored, because if a supply interruption
occurred while the ADC was sampling another channel
the interruption could be missed.
Kelvin
Sense
Traces
Sense Resistor
2052 Fig10
Figure 10. Kelvin-connected Sense Resistor
Each of the alarm signals can be used to change the status
of the following outputs: HEALTHY#, FAULT#,
FAULT_IRQ#, RST#, OV_IRQ#, and OC_IRQ#
Each channel can set the UV threshold anywhere in the
range from 0.9V to 6V in 20mV steps. OV thresholds are
offset from the UV threshold, and the value to be entered
into the register can be calculated from:
OV_TH – (UV_TH ×1.2)
UV_TH × 0.04 ^.
Environmental Automonitor Blocks
The 4 environmental channels, Channels 0 through 3, are
monitored autonomously by the internal logic of the
SMD1108 when it is in Automonitor mode and the indi-
vidual channels have been enabled. The ADC continuous
samples the input and compares the value against two
pre-programmed values held in a nonvolatile store.
When the UV threshold is enabled it is internally ORed to
the RST# signal. Please note if UV Override (UV_OVRD)
is active then these thresholds are ignored. UV Override
is provided to allow voltage margining during production
‘burning in’ of the line cards; this prevents Alarm signals
from being generated during this test. The over-current
comparator is offset from the input voltage by a program-
mable threshold, which can be set to 50, 75 or 150mV.
Selection of the sense resistor is made using Ohms Law,
for example:
Offset Voltage / Max Current = R sense
If a Two Amp limit using the 150mV threshold is specified,
it would require a resistance of 75mΩ.
Solid line
indicates
alert set if
conv = limit
Dashed line
indicates
alert NOT set
if conv = limit
Upper limit
Lower limit
3FF
ALERT
REGION
ALERT
REGION
000
"00"
3FF
ALERT
REGION
000
"10"
3FF
ALERT
REGION
ALERT
REGION
"01"
ALERT
REGION
000
Monitor
Option Bits
3FF x x
Lower
Upper
000
"11"
2052 Fig11
Figure 11. Alert Threshold Settings
26
2052 2.0 10/05/01
SUMMIT MICROELECTRONICS, Inc.