THS4524: ADS52J90 drive circuit

Toshihiro Watanabe

Genius 10235 points

Part Number: THS4524
Other Parts Discussed in Thread: ADS52J90, , TLV376, ADS1278

Hello,

We need to drive ADS52J90. Input signal is 50Hz/60Hz +/-10V. I made the drive circuit refering ADS52J90 datasheet.

Can you review the circuit and advise me what can it be improved?

ADS52J90_drive_circuit.TSC

I select THS4524 for lower number of devices because ADS52J90 is 16ch.

DC connection is selected because not wanted to use large capacitance due to low frequency.

TLV376 is for common mode buffer from ADC.

I am not sure THS4524 works as 1/20 attenuator because min gain is 1V/V even though it works in simulation.

I am wondering if around fc=10k RC low-pass filter is added for better SNR.

Best regards,

Toshihiro Watanabe

over 6 years ago

0 Toshihiro Watanabe over 6 years ago

TI__Genius 10235 points

Hello,

I found some mistaken. Please let me update the file.

I couldn't find the way to achieve single supply voltage then used +/-2.5V power supply.

1184.ADS52J90_drive_circuit.TSC

Best regards,

Toshihiro Watanabe

0 Jacob Freet over 6 years ago in reply to Toshihiro Watanabe

TI__Expert 8560 points

Hi Watanabe-san,

You are definitely correct that it will not be stable in a 1/20 attenuator configuration. The transient analysis in TINA doesn't always show oscillations, but you can reliably check stability by looking at the AC loop gain response and the corresponding phase margin. I've attached a circuit where you can see the phase margin is very unstable. If you need to use it in a 1/20 configuration it may be possible to compensate it with capacitors and make it stable, but we will need to add some components.

THS4524_Stability.TSC

Regards,

0 Toshihiro Watanabe over 6 years ago in reply to Jacob Freet

TI__Genius 10235 points

Hello Jacob-san,
Is there a training video or material to understand the stability? It would be helpful to share the link for understanding this.
Best regards,
Toshihiro Watanabe

0 Toshihiro Watanabe over 6 years ago in reply to Toshihiro Watanabe

TI__Genius 10235 points

Hello,

I tried to do the same simulation by datasheet page1 circuit as below. ADS1278 is not connected.

It seems this circuit don't have phase margin but I think this circuit works.

I am getting confused this simulation (or model) is able to use.

THS4524_stability_dual_loop.TSC

Did I mistake the circuit or misunderstood something?

Best regards,

Toshihiro Watanbae

0 Toshihiro Watanabe over 6 years ago in reply to Toshihiro Watanabe

TI__Genius 10235 points

Hello,

Read some material, Ccm and 2 x Cf seems needed to phase compensation.

Add 100pF between VIN+ and VIN- and 100pF in parallel with RF. I think noise gain will increase 12dB and pole made at 160kHz.

In AC analysis, no overshoot observed. It seems enough phase margin at open loop gain and noise gain cross point.

Do you think this circuit works?

THS4524.TSC

FDA_stability_1.TSC

Best regards,

Toshihiro Watanabe

0 Jacob Freet over 6 years ago in reply to Toshihiro Watanabe

TI__Expert 8560 points

Hello Watanabe-san,

Apologies for the late reply. Yes, the circuit you attached looks to be very stable. I don't expect any stability problems.

Regards,

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THS4524: ADS52J90 drive circuit