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Posted on May 03, 2018 at 14:22
Hello
Regarding the source current needed I might not clearly understood the configuration. The worst case would be Vout=5V and R=100
?
so the max current will be 50mA isn?t it?
Anyway let?s consider a current source max @100mA.
Regarding your question about the Isource in the datasheet:
The source current written in the datasheet represents a max current that the device can deliver when LMX358 is used in a saturated mode (actually in comparator) with a input voltage vid=1V. So in this configuration and without sourcing any current the output is 5V (by considering that the Opamp is power supplied by 5V). The Isource value parameter is given when the Output voltage reach Vout=0V. So this parameter express the maximum sourcing capability and not a regload current.
To get a better idea of the Vout degradation vs Isource current you must have a look to the figure 5 and 6 of the datasheet. It represents a typical behavior of the output (at different temperature) when an current is sinked/sourced.
To source a current from 50 to 100mA it would be better to use a TS982 Opamp (
).The figure 2 show the behavior of the TS982 of the output vs sourcing current. And you can see (@25°C) with a 50 mA source current you can typically expect a drop from the high rail of roughly 400mV, and with a 100 mA source current you can typically expect a drop from the high rail of roughly 650mV.
I hope I have correctly understood your point and this suggestion can match with your expectation. If not don?t hesitate to ask.
Best regards
Nicolas
Posted on May 03, 2018 at 14:22
Hello
Regarding the source current needed I might not clearly understood the configuration. The worst case would be Vout=5V and R=100
?
so the max current will be 50mA isn?t it?
Anyway let?s consider a current source max @100mA.
Regarding your question about the Isource in the datasheet:
The source current written in the datasheet represents a max current that the device can deliver when LMX358 is used in a saturated mode (actually in comparator) with a input voltage vid=1V. So in this configuration and without sourcing any current the output is 5V (by considering that the Opamp is power supplied by 5V). The Isource value parameter is given when the Output voltage reach Vout=0V. So this parameter express the maximum sourcing capability and not a regload current.
To get a better idea of the Vout degradation vs Isource current you must have a look to the figure 5 and 6 of the datasheet. It represents a typical behavior of the output (at different temperature) when an current is sinked/sourced.
To source a current from 50 to 100mA it would be better to use a TS982 Opamp (
).The figure 2 show the behavior of the TS982 of the output vs sourcing current. And you can see (@25°C) with a 50 mA source current you can typically expect a drop from the high rail of roughly 400mV, and with a 100 mA source current you can typically expect a drop from the high rail of roughly 650mV.
I hope I have correctly understood your point and this suggestion can match with your expectation. If not don?t hesitate to ask.
Best regards
Nicolas
