FAQ: Isolation >> Opto-Emulators >> Current FAQ
What are the different output types of TI Opto-emulators?
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FAQ: Isolation >> Opto-Emulators >> Current FAQ
What are the different output types of TI Opto-emulators?
What are the different output types of TI Opto-emulators?
Device |
Output Type |
ISO8710 |
CMOS |
ISO8711 |
Digital Open-Collector |
ISO811x |
Analog Open-Collector |
CMOS (Push-Pull) Output Type:
A CMOS (push-pull) output can source current in the high state or sink current in the low state. The digital push-pull configuration of opto-emulators is shown below:
Input State |
Output State |
Positive Driver (pFET ) |
Negative Driver (nFET ) |
LOW |
HIGH |
ON |
OFF |
HIGH |
LOW |
OFF |
ON |
When the output is in the high state:
When the output is in the low state:
Digital Open-Collector Output Type:
A digital open-collector output can only sink current in the low state. The digital open-collector configuration of opto-emulators is shown below:
Input State |
Output State |
Negative Driver ( nFET ) |
LOW |
Hi-Z |
OFF |
HIGH |
LOW |
ON |
When the output is in the high-impedance state, the n-channel MOSFET is off and does not allow any current to flow.
When the output is in the low state, the n-channel MOSFET is on and sinks current from the output to GND.
Analog Open-Collector Output Type:
An open-collector output for an analog opto-emulator device works differently than a traditional open-collector device. The analog open-collector configuration of opto-emulators is shown below:
In an analog opto-coupler, the open-collector output acts similarly to a “gain” of the input forward current. The CTR of the opto-emulator is a major factor in calculating the output current.
The table below shows how the CTR value for a given input forward current affects the output current when CTR is greater than 100% and also when CTR is less than 100%:
Input Forward Current (IF) |
Current Transfer Ratio (CTR) |
(CTR÷100) × IF = IC |
Output Current (IC) |
5 mA |
50 % |
2.5 mA |
|
5 mA |
100 % |
5 mA |
|
5 mA |
200 % |
10 mA |
|
5 mA |
400 % |
20 mA |
More information on CTR of an analog opto-emulator can be found here:
[FAQ] What is Current Transfer Ratio (CTR)? - TI E2E support forums