LP2901-Q1

www.ti.com................................................................................................................................................ SLCS148A – SEPTEMBER 2005 – REVISED APRIL 2008

Without transistor Q3, if the output voltage were allowed to drop below 0.8 V, transistor Q1 would saturate, and

the output current would drop to zero. The circuit would be unable to pull low current loads down to ground or the

negative supply, if used. Transistor Q3 has been included to bypass transistor Q1 under these conditions and

apply the current I1 directly to the base of Q2. The output sink current now is approximately I1 times the hFE of

Q2 (700

µA at V

O = 0.4 V). The output of the devices exhibits a bimodal characteristic, with a smooth transition

between modes.

In both cases, the output is an uncommitted collector. Several outputs can be tied together to provide a dot logic

function. An output pullup resistor can be connected to any available power-supply voltage within the permitted

power-supply range, and there is no restriction on this voltage, based on the magnitude of the voltage that is

supplied to VCC of the package.

Copyright © 2005–2008, Texas Instruments Incorporated

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