Supply Current

Question

Hello, 
 For the ADuM140D, I see a quiescent supply current in Table 1, as well as "total" supply current in Table 2. If I want to calculate the total current draw IDD1 or IDD2 for VDD1 and VDD2 supplies, would I go about that by summing the quiescent supply current figure from Table 1 to the "total" supply current figure from Table 2, and then adding in the drive strength of all 4 output pins? I.e., If we are driving all 4 outputs at 5 mA, and switching at 1 Mbps, then is total current draw for VDD2 equal to 4*(5 mA) + 3.7 mA (max spec. from table 2) + 2.92 mA (max spec from table 1)? Or is the quiescent current accounted for in the "Total" supply current figures from table 2? 
 Best

jnaso · Accepted Answer

Hi, 
 If this design isn't making use of the 'DISABLE' pin on the ADuM140D, the ADuM340E is a newer generation of OOK architecture. It consumes less power. Just an FYI if power is critical for this application. 
 Supply current for an OOK isolator depends on input signal and the output load. Each data channel has a independent transmitter on the input side and an independent receiver on the output side. The transmitter is active (and consuming more power) when the input detects the device's non-default state. As and example, the ADUM140D 1 (default high) will consume more power when the input is low and the transmitter is active. When a channel input sees the default state the transmitter for that channel is idle. This is the 'Q uiescent Supply Current' spec. Its all channels idle, or all channels transmitting. 
 Table 2, has all channels simultaneously operating at 1 Mbps, 25 Mbps and 100 Mbps (NRZ data format) with no load on the output. Said another way, its all channels with 500 kHz, 12.5 MHz and 50 MHz clock signals. Figure 12 and Figure 14 may be useful to see the nearly linear relationship between data rata and power consumption. 
 Applications typically aren't isolating 4 clocks, so consumption is going to depend on the actual data stream. 
 Remember to budget output side supply current for switching losses. The parasitic capacitance of the trace and presumably CMOS input stage the isolator's output is communicating with will consume power and increase supply current budgets. That c*V*f worth of supply current can get proportionally quite large with long traces and/or high data rates. 
 Regards, 
 Jason)

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Supply Current