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What is the reason when the output voltage drops below V-+0.7 V?

Latest Updated:10/01/2006

Question:

uPC844: The Japanese data sheet says in the "Cautions on use" that this IC stops sink current flow when the output voltage drops below V-+0.7 V. What is the reason?

Answer:

In the equivalent circuit in the data sheet, the output stage transistor (Q20) has an emitter-follower configuration. In order for this circuit to operate, an on-voltage of approximately 0.7 V required for the voltage between the emitter and base in Q20 to operate must be applied. Therefore, as a result, the controllable output voltage range is approximately 0.7 V on up, and the operational amplifier itself cannot output an output voltage lower than 0.7 V.


The OUTPUT SINK CURRENT LIMIT of VO-IO SINK characteristics has been included in the data sheet as reference data.
Suitable Products
Operational Amplifiers