ADP3166 datasheet(13/20 Pages) AD

13 / 20 page

REV. 0

ADP3166

–13–

4. Compute the relative values for RCS1, RCS2, and RTH using

A– B

r – A

– Br + B

– A

A– B

r – B

– A

r – A – B

1– A

–R

–

r– R

–R

–

CCS

()××

()××()×

()

(8)

5. Calculate RTH = rTH

RCS, then select the closest value of

thermistor available. Also compute a scaling factor k based on

the ratio of the actual thermistor value used relative to the

computed one:

TH ACTUAL

TH CALCULATED

()

(9)

6. Finally, calculate values for RCS1 and RCS2 using the following:

R= R

- k + k

××

()

(10)

For this example, RCS has been chosen to be 100 k

Ω, so we start

with a thermistor value of 100 k

Ω. Looking through available 0603

size thermistors, we find a Vishay NTHS0603N01N1003JR NTC

thermistor with A = 0.3602 and B = 0.09174. From these we

compute RCS1 = 0.3796, RCS2 = 0.7195 and RTH = 1.0751.

Solving for RTH yields 107.51 k

Ω, so we choose 100 kΩ, mak-

ing k = 0.9302. Finally, we find RCS1 and RCS2 to be 35.3 k

Ω

and 73.9 k

Ω. Choosing the closest 1% resistor values yields a

choice of 35.7 k

Ω and 73.2 kΩ.

Output Offset

AMD’s specification requires that at no load, the nominal output

voltage of the regulator be offset to a higher value than the nominal

voltage corresponding to the VID code. The offset is set by a con-

stant current source flowing out of the FB pin (IFB) and flowing

through RB. The value of RB can be found using Equation 11:

V– V

.V – . V

ONL

VID

153

1 5

200

Ω

(11)

The closest standard 1% resistor value is 2.00 k

Ω.

COUT Selection

The required output decoupling for the regulator is typically

recommended by AMD for various processors and platforms.

One can also use some simple design guidelines to determine

what is required. These guidelines are based on having both

bulk and ceramic capacitors in the system.

The first thing is to select the total amount of ceramic capaci-

tance, which is based on the number and type of capacitor to be

used. The best location for ceramics is inside the socket. Others

can be placed along the outer edge of the socket as well.

Combined ceramic values of 30

µF to 100 µF are recommended,

usually made up of multiple ceramic capacitors. Select the num-

ber of ceramics and find the total ceramic capacitance (CZ).

Next, there is an upper limit imposed on the total amount of

bulk capacitance (CX) when one considers the VID on-the-fly

voltage stepping of the output (voltage step VV in time tV with

error of VERR) and a lower limit based on meeting the critical

capacitance for load release for a given maximum load step

∆I

X MIN

VID

()

–

≥

××









∆

(12)

–1

– C

XMAX

VID

() ≤ ×× ×

××

























(13)

where K –In

ERR













To meet the conditions of these expressions and transient

response, the ESR of the bulk capacitor bank (RX) should be

less than or equal to the dynamic droop resistance, ROD. If the

CX(MIN) is larger than CX(MAX), the system will not meet the VID

on-the-fly specification and may require the use of a smaller

inductor or more phases (and may have to increase the switch-

ing frequency to keep the output ripple the same).

For our example, a combination of MLCC capacitors (CZ = 50

µF)

was used. The VID on-the-fly step change is from 1.5 V to 0.8 V

(making VV = 700 mV) in 100

µs with a setting error of 3%.

Solving for the bulk capacitance yields

FmF

X MIN

()

–.

≥

××











 =

600

31 9

1 5

1 63

Ω

.. V

. V

. m

––

mF =. mF

XMAX

() ≤

××

×× ×





















600

700

33 5

1 5

100

1 5

3 3 5 1 1

700

600

150

20 4

Ω

where K = 3.5.

Using eight 820

µF OSCONs with a typical ESR of 12 mΩ each

yields CX = 6.56 mF with an RX = 1.5 m

Ω.

One last check should be made to ensure that the ESL of the

bulk capacitors (LX) is low enough to limit the initial high fre-

quency transient spike. This is tested using

LmF

. mW =pH

≥×

250

1 9

361

(14)

ADP3166 датащи(PDF) 13 Page - Analog Devices

ADP3166 датащи(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL