L6986H datasheet(36/68 Pages) STMICROELECTRONICS

Part #	L6986H

Description	38 V, 2 A synchronous step-down switching regulator with 30 μA quiescent current

PDF	68 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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36 / 68 page

The sampling effect contribution FH(s) is: FH(s)= 1

1+ s

ωn⋅Qp+S2ωn2

(22)

where:

ωn=π⋅fSW

Qp= 1

π⋅[mc⋅(1−D)−0.5]

(23)

5.2

Error amplifier compensation network

The typical compensation network required to stabilize the system is shown in Figure 36. Transconductance

embedded error amplifier:

Figure 36. Transconductance embedded error amplifier

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:

A0(s)=

AV0⋅(1+s⋅RC⋅Cc)

s2⋅R0⋅(C0+Cp)⋅RC⋅Cc+s⋅(R0⋅Cc+R0⋅(C0+Cp)+Rc⋅Cc)+1

(24)

Where Avo = Gm · Ro

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

fPLF= 1

2⋅π⋅R0⋅Cc

(25)

fPHF= 1

2⋅π⋅R0⋅(C0+Cp)

(26)

L6986H

Error amplifier compensation network

DS12905 - Rev 2

page 36/68

L6986H Datasheet(PDF) 36 Page - STMicroelectronics