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MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

The transconductance error amplifier has a DC gain of

amplifier transconductance, which is 900FS (typ), and

cancel the output capacitor ESR zero if it occurs near

1 (0dB)). Thus:

dpEA

C

OUT,EA

C

1

f

2

C

(R

R )

=

π ×

×

+

zEA

C

C

1

f

2

C

R

=

π ×

×

pEA

F

C

1

f

2

C

R

=

π ×

×

below 1/5th of the switching frequency and much higher

SW

pMOD

C

f

f

f

5

<<

≤

The total loop gain as the product of the modulator gain,

the feedback voltage-divider gain, and the error-amplifier

FB

MOD(fC)

EA(fC)

OUT

V

GAIN

GAIN

1

V

×

×

=

pMOD

MOD(fC)

MOD(dc)

C

f

GAIN

GAIN

f

=

×

Therefore:

FB

MOD(fC)

m,EA

C

OUT

V

GAIN

g

R

1

V

×

×

×

=

OUT

C

m,EA

FB

MOD(fC)

V

R

g

V

GAIN

=

×

×

follows:

C

pMOD

C

1

C

2

f

R

=

π ×

×

F

zMOD

C

1

C

2

f

R

=

π ×

×

As the load current decreases, the modulator pole

also decreases; however, the modulator gain increases

accordingly and the crossover frequency remains the

same.

pMOD

MOD(fC)

MOD(dc)

zMOD

f

GAIN

GAIN

f

=

×

zMOD

EA(fC)

m,EA

C

C

f

GAIN

g

R

f

=

×

×

Therefore:

zMOD

FB

MOD(fC)

m,EA

C

OUT

C

f

V

GAIN

g

R

1

V

f

×

×

×

×

=

OUT

C

C

m,EA

FB

MOD(fC)

zMOD

V

f

R

g

V

GAIN

f

×

=

×

×

×

C

pMOD

C

1

C

2

f

R

=

π ×

×

as follows:

F

zMOD

C

1

C

2

f

R

=

π ×

×