LM6171: Can high-speed op amp based integrato be paralled to enhance the output capabilty

Yatao Ling1

Part Number: LM6171

Dear TI experts，

Simple question: I’ve used LM6171 as a non-inverting integrator and its output is buffered by parallel connection of several push-pulls as Fig1. In my experiment, the waveforms of G2 follows G1 very well(Their rise rate is about 100V-250V per us). But I soon test the i_B1 and i_B2 in Fig1 and find the currents is big, and they sum up to around 150mA, which is the output limit for LM6171.

Fig1

My question is can I parallel 2 integrators to enhance its output capability as Fig2? Of course, both integrators’ resistors and capacitors are the same.

Fig2

Best regards

over 6 years ago

0 Sean Cashin over 6 years ago

TI__Genius 17756 points

Hi Yatao,

Yes, this should be acceptable.

Best regards,

Sean

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Yatao,

I think it's better to have one single integrator for each single push-pull and to only parallel the outputs of push-pulls. By this the outputs of integrators are better isolated from each other. The 20R base resistors provide a comfortable isolation.

Kai

0 Yatao Ling1 over 6 years ago in reply to kai klaas69

Expert 1840 points

Hi Kai,

Actually I've driven 4 push-pulls(The other 2 aren't shown in my question). Then you mean that I should regulate my circuits as the schematic below??

Regards

0 kai klaas69 over 6 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

yes, that's what I meant.

Directly connecting the outputs of two LM6171 to each other is no good idea, because the output voltages might be different due to production tolerances of the components in the feedback loops or due to different offset voltages or slewing rates. Then the two LM6171's outputs might short circuit each other.

Kai

0 Yatao Ling1 over 6 years ago in reply to kai klaas69

Expert 1840 points

Thx!

0 Yatao Ling1 over 6 years ago in reply to Sean Cashin

Expert 1840 points

Hi sean,
Thx!!

0 kai klaas69 over 6 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

you could even consider splitting the 1R integrating resistor like shown below:

Kai

0 Yatao Ling1 over 6 years ago in reply to kai klaas69

Expert 1840 points

What advantage does such a topology have?

Plus: 1R is the RC load, not the integrating resistor.

0 kai klaas69 over 6 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

it would decrease the influence of mismatch between the push-pulls. But if the 1R is the load resistor, it cannot be split, right?

Kai

0 Yatao Ling1 over 6 years ago in reply to kai klaas69

Expert 1840 points

Hi Kai,
Thank you very much!
1R is indeed fixed in position, series-connected with 62nF.
But I'll take your advice and put a 0805 resistor for evry voltage-follower's emitter.If necessary, it will play a role . If not, I will just use 0R resistor. ^^
By the way, which part of the forum deals with the multiplexer issues?
Regards

0 kai klaas69 over 6 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

there's a special "Switches & Multiplexers Forum":

e2e.ti.com/.../388

Kai

0 Yatao Ling1 over 6 years ago in reply to kai klaas69

Expert 1840 points

Thx!

Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

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LM6171: Can high-speed op amp based integrato be paralled to enhance the output capabilty