LTM9012 datasheet(21/28 Pages) LINER

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LTM9012

9012f

applicaTions inForMaTion

GROUNDING AND BYPASSING

The LTM9012 requires a printed circuit board with a

clean unbroken ground plane. A multilayer board with an

internal ground plane in the first layer beneath the ADC is

recommended. Layout for the printed circuit board should

ensure that digital and analog signal lines are separated as

much as possible. In particular, care should be taken not

to run any digital track alongside an analog signal track

or underneath the ADC.

Bypass capacitors are integrated inside the package; ad-

ditional capacitance is optional.

The analog inputs, encode signals, and digital outputs

should not be routed next to each other. Ground fill and

grounded vias should be used as barriers to isolate these

signals from each other.

LAYOUT RECOMMENDATIONS

The pin assignments of the LTM9012 allow a flow-through

layout that makes it possible to use multiple parts in a

small area when a large number of ADC channels are

required. The LTM9012 has similar layout rules to other

BGA packages. The layout can be implemented with 6mil

blind vias and 5mil traces. The pinout has been designed

to minimize the space required to route the analog and

digital traces. The analog and digital traces can essentially

be routed within the width of the package. This allows

multiple packages to be located close together for high

channel count applications. Trace lengths for the analog

inputs and digital outputs should be matched as well as

possible.Table5liststhetracelengthsfortheanaloginputs

and digital outputs inside the package from the die pad to

the package pad. These should be added to the PCB trace

lengths for best matching.

Figures 7 through Figure 11 show an example of a good

PCB layout.

HEAT TRANSFER

Most of the heat generated by the LTM9012 is transferred

from the die through the bottom side of the package

through numerous ground pins onto the printed circuit

board. For good electrical and thermal performance, these

pins should be connected to the internal ground planes

by an array of vias.

Table 5. Internal Trace Lengths

NAME

(mm)

01A–

0.535

Q10

01A+

0.350

R11

01B–

2.185

R12

01B+

2.216

02A–

0.174

R10

02A+

0.667

S11

02B–

2.976

S12

02B+

2.972

03A–

3.033

03A+

3.031

03B–

0.752

03B+

0.370

04A–

2.130

04A+

2.125

04B–

0.332

04B+

0.527

A12

CH1–

7.741

A11

CH1+

7.723

CH2–

4.632

CH2+

4.629

CH3–

3.987

CH3+

3.988

CH4–

7.892

CH4+

7.896

CLK–

3.317

CLK+

3.325

0.241

DCO–

1.912

S10

DCO+

1.927

FR–

2.097

FR+

2.082

P10

PAR/SER

0.226

SCK

1.553

SD0

0.957

SDI

1.184

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