TLV9001: Usage of SHDN pin

The leakage current of the /SHDN pin, when pulled low, is specified as typically 150 nA. Assuming a voltage drop of at most 0.1 V over the resistor, you could use at most 666 kΩ. Use much less to compensate for the worst case. So 100 kΩ or 10 kΩ should be fine.

Hi,

this means a voltage drop of <0.2V at 150nA -> 1.3M. But since the 150nA is only a typical specification and can widely vary from chip to chip and with rising temperature I would choose a big reserve to safely override the internal pull-up. I think the pull-down should be in the kOhm range, no more than 10k.

Keep in mind, though, that the internal pull-up seems to be very very high, when such a huge pull-down of 1.3M is enough to force the voltage almost down to 0V. This means that when turning-off your pull-down only a very very high pull-up is present at the shutdown pin. So, with good reason, the datasheet "highly recommends" to directly connect a low or high voltage to this pin, as if the control voltage would come from a digital gate providing a low output impedance. With the huge internal pull-up alone even the least noise or EMI may make the shutdown pin toggle or introduce noise into the internal signal path of TLV9001.  

Keep also in mind that even when powering up the OPAmp in shutdown mode, you may see a glitch at the output until the supply voltage has reached the minimum operating supply voltage of OPAmp. Because of this I would recommend to perform some testing.

There's another issue: The supply current of TLV9001 is very low and the shutdown feature allows the supply current even to be considerably lowered. Using a pull-down resistor of 10k would cause a current of 500µA, on the other hand, which is ten times higher than the normal quiescent current of TLV9001. So, using a pull-down may be counterproductive, if you plan to achieve a very small total power consumption.

Kai

Hello,

Kai and Clemens are correct in their design recommendations for using a pull-down resistor with TLV900x.

Are you using the shutdown feature to isolate the signal path, or using the shutdown device for power savings?

This app note covers shutdown characteristics and considerations for TLV90xxS devices: “Designing for TLV90xxS Operational Amplifiers with Shutdown.”

Are you using the full bandwidth of the amplifier? TLV9041S does not have an internal pull-up or pull-down resistor on the shutdown pin. This may be a better choice for power savings (assuming you can tolerate the reduced specs of TLV9041S).

Best,

Jacob