TLV1805: Checking if usage conditions are supported

Hi Matt,

The supply voltages and input voltages are valid and within the recommended operating conditions. What sort of application is this comparator going to be used for? Do you have need of the shutdown pin that the TLV1805 has?

Thank you for the reply Ho!

I will pass this along to my customer and will have them comment back on this thread directly with answers to your questions in addition to any follow-up questions they may have!

-Matt

That is great! I am trying to use this as a buffer for an encoder with rather slow inputs (27 kHz for the main application and 500 kHz for an alternate application).

I do not have a need for the SHDN pin, but it appears to be active high.

1. Would SHDN support a 24v input?
2. Would a 2v input at SHDN suffice to overcome the shutdown and enable the outputs?
3. What is the current draw on SHDN at 5v?

Hi Marco,

Yes, the SHDN pin is active high. This means that if the SHDN pin is driven to a logic HIGH, shutdown will be on and the output will be Hi-Z. If the SHDN pin is driven to a logic LOW, shutdown will be off and the output will reflect the input state.

If there is no need for the shutdown functionality, then the SHDN pin can be connected to the V- of the device for TLV1805 to be always on.

I'll go ahead and answer your questions:

1. Would SHDN support a 24v input?

No, the SHDN pin has an absolute maximum voltage range of (V-) - 0.3V to (V-) + 5.5V. This means that applying 24V at the input could cause damage to the device.

2. Would a 2v input at SHDN suffice to overcome the shutdown and enable the outputs?

Please note that the device has a shutdown pin instead of an enable pin. An active shutdown pin shuts the device down, while an active enable pin enables the device. Per the datasheet electrical characteristics table, a voltage >2V will assert a logic HIGH on the SHDN pin and disable the output.

3. What is the current draw on SHDN at 5v?

The typical current flowing in/out of the SHDN pin is listed on the EC table:

There are also plots on figures 19 to 21 on the typical characteristics section of the datasheet that show the bias current of the SHDN pin.

If there is no need for the shutdown functionality, I'd like to suggest using the TLV1831 instead: TLV183x and TLV184x Family of 40V, High-Speed Comparators. TLV1831 is lower power and lower propagation delay than the TLV1805, which seems to be more applicable to your application.

Thank you for the clarifications. It appears that I can simply tie SHDN to V- and keep the outputs always active.

The TLV1832 could be interesting (I actually require two output channels). Two potential hurdles are:

1. I am not sure how to handle hysteresis with the difference in voltage between the input and output sides. Is this something you could shed some light on?
2. I will need to confirm if 30mA output is sufficient (compared to the 100mA sink/source output spec on the TLV1805)

Hi Marco,

1. I am not sure how to handle hysteresis with the difference in voltage between the input and output sides. Is this something you could shed some light on?

Matt provided some information on the input and output voltages, but could you please post a schematic of your comparator schematic in your application?

We have a guide on the calculations for implementing external hysteresis here: Inverting Comparator With Hysteresis Circuit.

That guide is using an open-drain device, so for your case you would just neglect the addition of the pull-up resistor. The output will pull up and down to approximately 0V and 24V, so the calculations for hysteresis on the non-inverting terminal of the comparator will have to be with a 0 to 24V swing.

2. I will need to confirm if 30mA output is sufficient (compared to the 100mA sink/source output spec on the TLV1805)

Yes, the TLV1805 has a stronger output stage than the TLV1832. What kind of load is the output of the comparator expected to drive?