Calculation of SuMMIT Current Utilization (9/99)

UTMC Application Note
Calculation of Sµ
µMMITTM E Stand-Alone Current Utilization
The following describes the typical supply current consumed by the SµMMIT E protocol device (UT69151E) during
1553 message processing. Within the SµMMIT E package drawing current is the JA01 protocol die (figure 1). Considering the SµMMIT’s power saving architecture, it is appropriate to calculate supply current with respect to some
reference of message rate or duty cycle. Therefore, characterization data and device specifications exist for 0%, 25%,
50%, 87.5%, and 100% duty cycles. These percentages comprehend actual intermessage gap and RT response times
defined by the 1553 bus protocol (i.e. 12µs and 4µs, respectively). In rare cases where a maximum number of data
words are transferred, the protocol circuitry operates at just above 90% duty cycle, well below the maximum rating.
Note: Characterization and specification data do not usually include 100% duty cycle by definition of 1553 not that
the devices can not operate at this maximum.
(unused for
JA01 die
Figure 1. Sµ
µMMIT E Device
With regard to the current consumption during 1553 message processing, the JA01 circuitry facilitates 1553 operations. This situation is comprehended by data specified in the SµMMIT handbook for the stand-alone device. Table 1
relates typical test data collected, at worst case temperature and voltage, for the stand-alone SµMMIT part in comparison to 40mA standby current specified within the SµMMIT handbook (Chapter 16). Using specification data and
typical characterization data at various duty cycles simplifies power and supply current calculations required by the
Using information provided by the table on the next page, it is possible to generate total current and subsequent
power consumption by the SµMMIT E during 1553 processing.
Latest Revision Date:
Original Publication Date: 9/20/1999
Page 1 of 3
UTMC Application Note
Table 1. SuMMIT Current vs. Duty Cycle
35 35.1 35.8
Supply Current 30
typical test
spec. values
Duty Cycle
At 0% duty cycle the observed current consumption for the stand-alone SµMMIT E is 3.3mA. Using values for each
duty cycle provide the following results:
0% ISµMMIT E = 3.3mA
25% ISµMMIT E = 22.8mA
50% ISµMMIT E = 27.6mA
87.5% ISµMMIT E = 35.0mA
100% ISµMMIT E = 35.8mA
Multiplying these total currents by the nominal voltage supply value of 5 Volts provides the following power consumption equations per respective duty cycle:
0% PSµMMIT E = 5V(3.3mA) = 0.017 Watts
25% PSµMMIT E = 5V(22.8mA) = 0.114 Watts
50% PSµMMIT E = 5V(27.6mA) = 0.138 Watts
87.5% PSµMMIT E = 5V(35.0mA) = 0.175 Watts
100% PSµMMIT E = 5V(35.8mA) = 0.179 Watts
Latest Revision Date:
Original Publication Date: 9/20/1999
Page 2 of 3
UTMC Application Note
From the above it can be seen that under the most intensive 1553 message processing the SµMMIT E consumes considerably less than a fifth of a Watt of power. For the sake of comparison it might be worth noting and calculating
absolute worst case power consumption by considering the very guard-banded specification value at 100%. Using
data from the table above provides the following:
100%rated ISµMMIT E = 40.0mA
Then calculate power using maximum voltage rating:
100%rated PSµMMIT E = 5.5V(40.0mA) = 0.22 Watts
Latest Revision Date:
Original Publication Date: 9/20/1999
Page 3 of 3