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Which point of IBIAS must be careful during circuit design of uPC2933A?

Latest Updated:12/01/2006

Question:

Which points regarding the quiescent current (IBIAS) specification should one be careful of during circuit design using the uPC2933A?

Answer:

IBIAS is a current necessary for each internal block of the power IC to operate in the steady state, and defines a current that flows from an input pin to a GND pin.
In addition, the startup quiescent current (IBIAS(S)) must also be noted.
A low dropout voltage regulator such as the uPC2900 series uses a PNP transistor as the output-stage transistor. This transistor is saturated and a high current flows from the input pin to the GND pin when the input voltage is low at startup. The startup quiescent current is the maximum value of this current. The regulator does not operate correctly unless the startup quiescent current flows.

[Example of uPC2933A]

Item Symbol Conditions MIN. TYP. MAX. Unit
Quiescent current IBIAS Io=0A   2.0 3.0 mA
Startup quiescent current IBIAS(s) VIN=3.1V,Io=0A   10 30 mA




The quiescent current in this example indicates that ICs require IBIAS of 2.0 mA on average to operate in the steady state, and that ICs through which up to 3.0 mA flows are included.
Similarly, it indicates that ICs through which a startup quiescent current of up to 30 mA flows are included.
Therefore, an external power supply that can supply a current of at least 30 mA to the input pins of the ICs is necessary, in addition to the current that flows into the circuit load.

Suitable Products
CMOS Operational Amplifiers
Bipolar Operational Amplifiers
3 Terminal Regulators