BUF634 driven by square waveform

paulo barroso

Other Parts Discussed in Thread: BUF634, LME49860, TINA-TI

Hi,

I am currently using the BUF634 in the following configuration:

Vcc=+18V & Vee=-18V.

I am puzzled because when I increase the load around 20mA, the BUF634, when driven with a square waveform ±16V @ 50Hz, presents some strange spikes at around 240 KHz as depicted here below on the positive edge.

Am I using it at a limit I am not aware of?

Do you know what can cause this behaviour?

One thing for sure, when I decrease the input amplitude those spikes vanish. Moreover those spikes can be filtered by increasinf the capacitor in the feedback while reducing the bandwidth.

Regards.

Paulo-Jorge BARROSO.

over 11 years ago

0 paulo barroso over 11 years ago

Prodigy 130 points

Hi,

I need help to overcome this issue. Can anyone help me ?

Regards.

Paulo-Jorge BARROSO.

0 Hooman Hashemi over 11 years ago in reply to paulo barroso

TI__Mastermind 22825 points

Hello Paulo,

From the BUF634 datasheet, I'd say that +/-16V output swing (with Vs=+/-18V resulting in 2V headroom to either rail), might be a little too close to the edge when you have 20mA output current. From this BUF634 plot, you'd need at least 2.5V typical headroom to either supply with x-axis= 20mA. Production limit may require even more guard band / headroom:

BUF634:

You have even a bigger limitation with OP37 where the table below shows you must allow 5V headroom (10V with 15V supply) from either supply:

OP37:

If you need +/-16V output swing, you may think about replacing OP37 with a higher swing device, or raising your supply voltage even further.

Here are some low noise devices with +/-18V capability that have only a 1V headroom requirement (to ease large output swing), for your review:

LHV870
LME49870
LMP8671

Regards,

Hooman

0 paulo barroso over 11 years ago in reply to Hooman Hashemi

Prodigy 130 points

Hi Hooman,

thanks a lot for your clear and detailed reply. I will consider using one of the parts you suggested to replace the OP37.

Happy new year.

Paulo.

0 paulo barroso over 11 years ago in reply to paulo barroso

Prodigy 130 points

Hi Hooman,

is there any model for the LME49870 audio OP amp ?

Regards.

Paulo.

0 Hooman Hashemi over 11 years ago in reply to paulo barroso

TI__Mastermind 22825 points

Hi Paulo,

The LME49870 (Single) does not have a TINA-TI model, but LME49860 (Dual) does and the electrical characteristics are identical. So, you can use the LME49860 instead.

Regards,

Hooman

0 Hooman Hashemi over 11 years ago in reply to Hooman Hashemi

TI__Mastermind 22825 points

Hello again Paulo,

In case you could not locate the LME49860 TINA-TI model off the web (it does not show up there), I've attached it below. You can get it if you open TINA-TI and search for it under "Find Component" (icon showing finger pointing to the right on the upper RHS, shown below):