ADS1625IPAPR datasheet(28/37 Pages) TI

28 / 37 page

ADS1625

ADS1626

SBAS280E − JUNE 2003 − REVISED MAY 2007

www.ti.com

LAYOUT ISSUES

The ADS1625/6 is a very high-speed, high-resolution data

converter. In order to achieve the maximum performance,

careful attention must be given to the printed circuit board

(PCB) layout. Use good high-speed techniques for all

circuitry. Critical capacitors should be placed close to pins

as possible. These include capacitors directly connected

to the analog and reference inputs and the power supplies.

Make sure to also properly bypass all circuitry driving the

inputs and references.

There are two possible approaches for the ground plane on

the PCB: a single common plane or two separate planes, one

for the analog grounds and one for the digital grounds. When

using only one common plane, isolate the flow of current on

pin 58 from pin 1; use breaks on the ground plane to

accomplish this. Pin 58 carries the switching current from the

analog clocking for the modulator and can corrupt the quiet

analog ground on pin 1. When using two planes, it is

recommended that they be tied together right at the PCB. Do

not try to connect the ground planes together after running

separately through edge connectors or cables as this

reduces performance and increases the likelihood of latchup.

In general, keep the resistances used in the driving circuits

for the inputs and reference low to prevent excess thermal

noise from degrading overall performance. Avoid having

the ADS1625/6 digital outputs drive heavy loads. Buffers

on the outputs are recommended unless the ADS1625/6

is connected directly to a DSP or controller situated

nearby. Additionally, make sure the digital inputs are

driven with clean signals as ringing on the inputs can

introduce noise.

The ADS1625/6 uses TI PowerPAD technology. The

PowerPAD is physically connected to the substrate of the

silicon inside the package and must be soldered to the

analog ground plane on the PCB using the exposed metal

pad underneath the package for proper heat dissipation.

Please refer to application report SLMA002, located at

www.ti.com, for more details on the PowerPAD package.

APPLICATIONS

INTERFACING THE ADS1625 TO THE

TMS320C6000

Figure 28 illustrates how to directly connect the ADS1625

to the TMS320C6000 DSP. The processor controls

reading using output ARE. The ADS1625 is selected using

the DSP control output, CE2. The ADS1625 18-bit data

output bus is directly connected to the TMS320C6000 data

bus. The data ready output from the ADS1625, DRDY,

drives interrupt EXT_INT7 on the TMS320C6000.

DOUT[17:0]

ADS1625

DRDY

XD[17:0]

TMS320C6000

EXT_INT7

CE2

ARE

Figure 28. ADS1625—TMS320C6000 Interface

Connection

INTERFACING THE ADS1626 TO THE

TMS320C6000

Figure 29 illustrates how to directly connect the ADS1626

to the TMS320C6000 DSP. The processor controls

reading using output ARE. The ADS1626 is permanently

selected by grounding the CS pin. The ADS1626 18-bit

data output bus is directly connected to the TMS320C6000

data bus. The data ready output from the ADS1626,

DRDY, drives interrupt EXT_INT7 on the TMS320C6000.

DOUT[17:0]

ADS1626

DRDY

XD[17:0]

TMS320C6000

EXT_INT7

ARE

Figure 29. ADS1626—TMS320C6000 Interface

Connection

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