ADS5553IPFP datasheet(21/27 Pages) TI2

21 / 27 page

ADS5553

SLWS158 − FEBRUARY 2005

www.ti.com

OUTPUT INFORMATION

Each of the two ADCs provide 14 data outputs in two’s

complement format (D13 to D0, with D13 being the

MSB and D0 the LSB), a data-ready signal (CLKOUT),

and an out-of-range indicator (OVR) that equals 1 when

the output reaches the full-scale limits.

In addition, output enable control (pins 48 and 52) are

provided to tri-state the outputs. See Table 2 for details.

The output circuitry of the ADS5553 has been designed

to minimize the noise produced by the transients of the

data switching and in particular its coupling to the ADC

analog circuitry. Output D0 senses the load capacitance

and adjusts the drive capability of all the output pins of

the ADC to maintain the same output slew rate

described in the timing diagram of Figure 1, as long as

all outputs (including CLKOUT) have a similar load as

the one at D0. This circuit also reduces the sensitivity

of the output timing versus supply voltage or

temperature. External series resistors with the output

are not necessary.

PowerPAD PACKAGE

The PowerPAD package is a thermally enhanced

standard size IC package designed to eliminate the use

of bulky heatsinks and slugs traditionally used in

thermal packages. This package can be easily mounted

using standard printed circuit board (PCB) assembly

techniques, and can be removed and replaced using

standard repair procedures.

The PowerPAD package is designed so that the

leadframe die pad (or thermal pad) is exposed on the

bottom of the IC. This provides an extremely low

thermal resistance path between the die and the

exterior of the package. The thermal pad on the bottom

of the IC can then be soldered directly to the printed

circuit board (PCB), using the PCB as a heatsink.

Assembly Process

1. Prepare the PCB top-side etch pattern including

etch for the leads as well as the thermal pad as

illustrated in the Mechanical Data section.

2. Place a 5-by-5 array of thermal vias in the thermal

pad area. These holes should be 13 mils in

diameter. The small size prevents wicking of the

solder through the holes.

3. It is recommended to place a small number of 25 mil

diameter holes under the package, but outside the

thermal pad area to provide an additional heat path.

4. Connect all holes (both those inside and outside the

thermal pad area) to an internal copper plane (such

as a ground plane).

5. Do not use the typical web or spoke via connection

pattern when connecting the thermal vias to the

ground plane. The spoke pattern increases the

thermal resistance to the ground plane.

6. The top-side solder mask should leave exposed the

terminals of the package and the thermal pad area.

7. Cover the entire bottom side of the PowerPAD vias

to prevent solder wicking.

8. Apply solder paste to the exposed thermal pad area

and all of the package terminals.

For more detailed information regarding the PowerPAD

package and its thermal properties, see either the

SLMA004B Application Brief PowerPAD Made Easy or

the SLMA002 Technical Brief PowerPAD Thermally

Enhanced Package.

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