ADM1014

–12–

REV.

PrN 1/02

LAYOUT CONSIDERATIONS

Any circuits supplied by the ADM1014 are outside the control

loops of the main system power supplies, which means that any

series resistance between the four supply inputs and the out-

puts will cause a degradation of the supply load regulation. This

includes connector contact resistance, PCB trace resistance, on-

resistance of MOSFETs (both external and on-chip) and

current sense resistors.

Care must therefore be taken to ensure that:

a) PCB traces are as heavy as possible.

b)External MOSFETs have low-on resistance.

c) Current sense resistors are as small as possible.

The current sense resistors have very small values (5m

in the

preceding example) to minimise the voltage drop across them.

Because of this, PCB trace resistance can be a significant per-

centage of the sense resistance. It is therefore essential to en-

sure that the ADM1014 senses the voltage drop directly across

the sense resistors and not across any current-carrying trace

resistance in series with them. Connections from the ADM1014 to

the sense resistors must go directly to the ends of the resistors.

Figure 4 shows examples of good and bad practice

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

38-Pin TSSOP (RU-38)

INCORRECT

35

34

37

36

22

21

24

23

CURRENT

SENSE

RESISTORS

VSENSE

ADM1014

VSENSE

CORRECT

ADDITIONAL

VOLTAGE DROP

ADDITIONAL

VOLTAGE DROP

CURRENT

SENSE

RESISTORS

VSENSE

ADM1014

VSENSE

ADDITIONAL

VOLTAGE DROP

ADDITIONAL

VOLTAGE DROP

35

34

37

36

22

21

24

23

34

21

Figure 4. Good and Bad Practice For Sense Resistor

Connection

38

20

19

1

0.386 (9.80)

0.378 (9.60)

0.256 (6.50)

0.246 (6.25)

0.177(4.50)

0.169(4.30)

PIN 1

SEATING

PLANE

0.006(0.15)

0.002(0.05)

0.0200(0.50)

BSC

0.0433 (1.10)

MAX

0.0106 (0.27)

0.0067 (0.17)

0.0079 (0.20)

0.0035 (0.090)

0.028 (0.70)

0.020 (0.50)

88

08