TPL8002-25: RG RF and RSW value if not to use operational amplifier

Hi Katlynne，

Thank you very much for your reply. 

Thanks for your answer sincerely. But if I want to use only the value of RF in series to a certain circuit, can it be achieved? I hope it can be used as a sliding rheostat for me.

Best regards

Kailyn 

Ok, I understand your explanation. And can I add a resistance of the external circuit and  connect it parallel with the RF? If I need a smaller resistance value.

Thanks a lot ! I’m really appreciate it!

Hi Kuijun and Kailyn,

Not a problem. Please let me know if you have any additional questions.

Best,

Katlynne Jones

I used tpl8002-25 in parallel with a resistor to test its high-frequency performance, output a square wave of 8MHz or lower to the F interface (two different resistor dividers), and then measured the voltage across the parallel resistor. Logically, the voltage at both ends should also have two square waves with the same frequency, but the waveform effect is bad. 

Hi Kuijun,

Can you share a schematic of your setup and a screenshot of the the scope shot of the input and output waveform you are seeing. 

Thank you,
Katlynne

I connect VDD VEE with 3V, -3V voltage，Give F a square wave with a different frequency, 50KHz、500KHz、1MHz.According to the test below, the measured voltage value is no problem, When the frequency is high, the voltage value will be wrong, and the waveform page will be bad

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I found that after connecting resistors in parallel, the adjustable range is very small. If I want to get the resistance value range of 30-260, is there a way to do it?

Hi Kuijun, 

The 8MHz bandwidth spec given in the datasheet is for a voltage being applied to one of the resistor terminals (seen in the figure below), not the digital control pins. There is no spec for the output response time due to a change on a digital control pin. The high frequency square wave you are trying to input on the control pin is likely exceeding that spec which is why you see the bad response. In the first scope shot, it looks like it takes about 5us for the resistance to reach the desired value, this would lead to about a 200kHz waveform. In your 500kHz waveform you can see that the output square wave does not have enough time to reach the max value like in 100kHz waveform. 

I don't see a way to get the 30-260 range due to the formula for parallel resistance values.

Best,

Katlynne Jones

So in this case, the high frequency can only almost reach 200KHz, right?

Hi Kuijun,

That is what I am concluding based on the scope shots you have sent me. The device doesn't have a spec for this implementation. You can go past 200kHz but you will start seeing the degraded waveforms like you shared due to the device not being able to respond to the interface controls fast enough.

Best,

Katlynne Jones