REV. 0

–16–

ADP3166

The first step is to compute the time constants for all of the poles and zeros in the system:

R= n

R

+ A

R

+

RV

V

+

R+ R

L

– n

D

V

nC

R

R

V

R=

. m

+

. m

+

.m

.

V

.V

+

.m

+ . m

nH

– .

eOD

D

DS

LRT

VID

OOD

RT

XO

OD

VID

e

××

×

×

××

×

×

××

×

Ω

1

31 9

5 4 2

16

048

15

11

19

600

10 375

0

ΩΩ

Ω

Ω

..V

.mF

. m

. m. V

R=

. m

e

48

36 56

1 1

19

15

36 0

××

×

×

ΩΩ

Ω

(25)

T= C

R

– R +

L

R

R– R

R

T= 6.56 mF

1.9 m

– 0.6 m

+

375 pH

1.5 m

1.9 m

– 0.6 m

1.5 m

T= 8.70

s

aX

OD

'

X

OD

OD

'

X

a

a

×

()

×

×

()

×

ΩΩ

Ω

ΩΩ

Ω

µ

(26)

T= R + R – R

C

T=

.

+ . m

– . m.

mF =.

s

bX

'

OD

X

b

ΩΩ

Ω

15

06

19

656

1 31

m

(27)

T=

VL –

AR

2f

VR

T=

.V

nH –

.m

kHz

.. m

=.

s

c

RT

DDS

SW

VID

e

c

×

×

×













×

×

×

×













×

µ

048

600

54 2

2

330

15

36 0

505

Ω

Ω

V

(28)

T=

CC

R

CR – R + C

R

T=

.mF

mF

. m

.mF

. m – . m

+

mF

. m

=7 ns

d

XZ

OD

XO

Z

OD

d

××

×

()

×

××

Ω

×Ω

Ω

()

×Ω

2

2

656

50

1 9

656

1 9

0 6

50

1 9

13

(29)

C=

T

R

=

ns

.k

=. pF

FB

d

A

137

733

18 7

Ω

(33)

Choosing the closest standard values for these components yields:

Figure 3 shows the typical transient response using the compen-

sation values.

In continuous inductor-current mode, the source current of the

high-side MOSFET is approximately a square wave with a duty

ratio equal to n

maximum output current. To prevent large voltage transients, a

low ESR input capacitor sized for the maximum rms current

must be used. The maximum rms capacitor current is given by

I= D

I

nD

–

I=

A

.

–= .

A

CRMS

O

CRMS

××

×

××

×

1

1

0 125

56

1

3

125

19 05

.

(34)

Note that the capacitor manufacturer’s ripple current ratings are

often based on only 2,000 hours of life. This makes it advisable

where, for the ADP3166, R' is the PCB resistance from the bulk

equals 0.48 V, R' is approximately 0.6 m

Ω (assuming a 4-layer

A type-three compensator on the voltage feedback is adequate for

proper compensation of the output filter. The expressions that

follow are intended to yield an optimal starting point for the design;

some adjustments may be necessary to account for PCB and com-

ponent parasitic effects (see the Tuning Procedure section).

The compensation values can then be solved using the following:

C=

nR

T

RR

C=

.m

.

s

.m

.

k

=pF

A

OD

a

eB

A

××

×

××

µ

×

31 9

8 70

36 0

2 00

689

Ω

ΩΩ

(30)

C=

T

R

=

.s

.k

=pF

B

b

B

131

200

655

µ

Ω

(31)

C=

T

R

=

.s

.k

=pF

B

b

B

131

200

655

µ

Ω

(32)