ST1CC40 Datasheet, PDF(14/37 Page) STMicroelectronics – 3 A monolithic step-down current source with synchronous rectification

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ST1CC40 Datasheet, PDF (14/37 Pages) STMicroelectronics – 3 A monolithic step-down current source with synchronous rectification

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Application notes

Figure 6. Transconductance embedded error amplifier

ST1CC40

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RC and CC introduce a pole and a zero in the open loop gain. CP does not significantly affect

system stability but it is useful to reduce the noise at the output of the error amplifier.

The transfer function of the error amplifier and its compensation network is:

Equation 8

A0ï¨sï© = s----2----ï---R----0----ï---ï¨---C----0-----+----C-----p---ï©----ï---R----c----ï---C--A---c-V--+-0----s-ï---ï¨-ï-1--ï¨--R-+----0-s---ï-ï--C-R---c--c--+--ï---CR----c-0--ï©--ï---ï¨--C-----0----+-----C----p---ï©----+-----R----c----ï---C-----c--ï©----+-----1--

where Avo = Gm Â· Ro.

The poles of this transfer function are (if Cc >> C0 + CP):

Equation 9

fP LF = -2----ï---ï°-----ï---1R-----0----ï---C----c-

Equation 10

fP HF = -2----ï---ï°-----ï---R-----c----ï1---ï¨--C-----0----+-----C----p---ï©

whereas the zero is defined as:

Equation 11

FZ = -2----ï---ï°-----ï---1R-----c----ï---C----c-

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