OPA2990: temp drift

Chen Alex1

Expert 2175 points

Part Number: OPA2990
Other Parts Discussed in Thread: CSD17585F5, CSD25501F3

hi sir

below figure is a DC to 4-20mA circuit

Vout_A is DAC ouput

OUT1 is 4-20mA output

the output current will rasing when current over 12mA ,out of spec

did you have any advise?

thanks

16 days ago

0 Clemens Ladisch 16 days ago

Guru 246390 points

When Vout_A is at some value between 0.12 V and 0.2 V, what are the voltages at pins 3, 2, 5, 6, and 7?

0 Ron Michallick 16 days ago

TI__Guru*** 140706 points

Hello Chen,

The VCM for U30B varies from (12V-0.4V) at 4mA to (12V-2V) at 20mA

Near 12mA, the op amp switches between input transistors. This makes 4 to 10mA not quite match 15 to 20mA

Does that explain your data?

0 Ron Michallick 16 days ago in reply to Ron Michallick

TI__Guru*** 140706 points

Chen

The thread name says 'temp drift'. Keep in mind the the base currents lost in the current mirrors vary with transistor beta. Beta varies with temperature. You could change to NMOS and PMOS to eliminate base current.

0 Chen Alex1 15 days ago in reply to Ron Michallick

Expert 2175 points

hi Sir

Did you mean the output current drift ,due to the Transistor beta?

did you have any suggest TI NMOS or PMOS?

thanks

0 Ron Michallick 15 days ago in reply to Chen Alex1

TI__Guru*** 140706 points

Chen,

Yes transistor beta

I'm not an expert in this product line, but here is a starting point. You can ask a new question with one of these part numbers, to reach an expert.

CSD17585F5 NMOS Q8

CSD25501F3 PMOS Q2

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OPA2990: temp drift