Electrical – LT1010 (Unitay Gain Buffer) – Voltage output depends on load? (LTSpice simulation)


I need to drive a TTL signal into a 50ohm load (connected to a 5V supply, not to the ground) from a DAQ card that can only output 5mA.
I therefore looked around and found Linear Technology has LT1010, which is a buffer with 150mA current capability.

It should be very simple to use, but when trying to simulate it using LTspice, I get very weird results.
I've attached a picture of my schematic (sorry it's ugly, was supposed to be a quick and dirty simulation):

When I set the input to 5V, everything is OK. But when I set it to 0V, The output is reaching 1.2V.

The bias 20ohm resistor can be changed to any value from 0 (no resistor) to 1k and it doesn't change anything, I've also tried adding a negative supply to the V-, but it doesn't change much.

According to the LT1010 spec, it should be able to drive a 150mA load, doesn't it means that the output should follow the input (up to a small offset) up to 150mA?

Best Answer

Look at the negative saturation voltage curve in the datasheet. If you operate this part with a single supply, the output won't be able to swing to ground. At 25C with 150mA load you will only be able to get down to about 2.9V. This isn't really meant for digital applications like this, you should look for a high current digital buffer or maybe a discrete circuit.

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