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LMX358IQ2T Output Current Capability

Dave Kearney
Associate II
Posted on May 03, 2018 at 05:29

Hi, I'm looking for an op-amp to buffer a signal and provide an output of 2 -> 5V to a load of 100 - 200R. This would require driving the load with 50 - 100 mA. The LMX358IQ2T has a specified output source current of 60-70 mA, but I'm not sure if this just means an absolute max or a max where the output voltage signal will be maintained? Will the voltage output have degraded substantially at roughly this current? If so, what are my options for op-amps capable of driving 50-100mA over 2-5V without significant degradation?

Many Thanks,

Dave

1 ACCEPTED SOLUTION

Accepted Solutions
AUPETIT nicolas
Associate III
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 (

https://produktinfo.conrad.com/datenblaetter/1100000-1199999/001184372-da-01-en-IC_OP_AMP_DUAL_BIP_TS982IYDWT_SOIC_8_STM.pdf

).0690X00000604goQAA.jpg

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

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3 REPLIES 3
AUPETIT nicolas
Associate III
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 (

https://produktinfo.conrad.com/datenblaetter/1100000-1199999/001184372-da-01-en-IC_OP_AMP_DUAL_BIP_TS982IYDWT_SOIC_8_STM.pdf

).0690X00000604goQAA.jpg

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 07, 2018 at 04:13

Many thanks Nicolas. That was a great help. Is there a single package version of the TS982?

Many Thanks,

Dave

Posted on June 28, 2018 at 15:04

Hi David

I'm really sorry for my so late answer, this post escape to my box ...

Anyway unfortunately not TS982 is available only in dual package.

BR

nicolas