ADP3167JR datasheet(12/16 Pages) AD

12 / 16 page

REV. B

–12–

ADP3160/ADP3167

sensing when the current threshold has been reached and when

the high-side MOSFET actually turns off. These two factors are

combined with the inherent voltage at the output of gm amplifier

that commands a current sense threshold of 0 mV (VGNL0):

GNL

L RIPPLE

SENSE

AVG

SENSE

¥¥

¥¥ ¥

()

VV +

V– .

. = .

GNL

¥¥

12 2

12 5

1 635

600

260

12 51 201

–

(23)

The output voltage at no load (VONL) can be calculated by

starting with the VID setting, adding in the positive offset (V+),

subtracting half the ripple voltage, and then subtracting the

dominant error terms:

ONL

VID

WIN

VID

+¥

ËÁ

¯˜

(24)

ONL

W¥

¥+

ËÁ

¯˜

138

9 9

0007

002

1 681

–

.( .

)

With these two terms calculated, the divider resistors (RA

for the upper and RB for the lower) can be calculated.

Assuming that the internal resistance of the gm amplifier

(ROGM) is 200 k

REF

GNL

ONL

VID

-¥

–

()

(25)

mmho

-¥

31 2

757

1681

10 73

.( .

– .

)

Choosing the nearest 1% resistor value gives RB = 11.0 k

Finally, RA is calculated:

OGM

111

757

200

11 3

25 86

(26)

Again, choosing the nearest 1% resistor value gives RA = 26.1 k

The compensating capacitor can be calculated from the equation:

OUT

E MAX

OSC

- ¥¥

()

(27)

kHz

¥W

¥¥

19 8

1 5

757

400

7 57

The closest standard value for COC is 3.3 nF.

The resistance of the zero-setting resistor in series with the

compensating capacitor is:

kHz

OSC

¥¥

400

482

(28)

The nearest standard 5% resistor value is 470

W. Note that this

resistor is only required when COUT approaches CCRIT (within

25% or less). In this example, COUT > CCRIT, and RZ can there-

fore be omitted.

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