LM2743MTCSLASHNOPB datasheet(26/44 Pages) TI2

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GEA-ACTUAL x OPG

HEA =

1 + GEA-ACTUAL+ OPG

Z1 =

RC2 +

sCC3

RC1 + RC2

sCC3

RC1

ZF =

sCC1

x 10,000 +

sCC2

10,000 +

sCC1

sCC2

GEA-ACTUAL =

RC2 =

2S x CC3 x fP1

= 2.55 k:

RC1 =

2S x CC2 x fZ1

= 39.8 k:

CC3 =

2S x 10,000

= 2.73 nF

fZ2

fP1

LM2743

SNVS276I – APRIL 2004 – REVISED FEBRUARY 2019

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Typical Applications (continued)

(39)

(40)

(41)

In practice, a good trade off between phase margin and bandwidth can be obtained by selecting the closest

±10% capacitor values above what are suggested for CC1 and CC2, the closest ±10% capacitor value below the

suggestion for CC3, and the closest ±1% resistor values below the suggestions for RC1, RC2. Note that if the

suggested value for RC2 is less than 100Ω, it should be replaced by a short circuit. Following this guideline, the

compensation components will be:

CC1 = 27 pF ±10%

CC2 = 820 pF ±10%

CC3 = 2.7 nF ±10%

RC1 = 39.2 kΩ ±1%

RC2 = 2.55 kΩ ±1%

The transfer function of the compensation block can be derived by considering the compensation components as

impedance blocks ZF and ZI around an inverting op-amp:

(42)

(43)

(44)

As with the generic equation, GEA-ACTUAL must be modified to take into account the limited bandwidth of the error

amplifier. The result is:

(45)

The total control loop transfer function H is equal to the power stage transfer function multiplied by the error

amplifier transfer function.

H = GPS x HEA

(46)

LM2743MTC/NOPB Datasheet(PDF) 26 Page - Texas Instruments

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