TLV1571, TLV1578

2.7 V TO 5.5 V, 1-/8-CHANNEL, 10-BIT,

PARALLEL ANALOG-TO-DIGITAL CONVERTERS

SLAS170C –MARCH 1999 – REVISED FEBRUARY 2000

16

POST OFFICE BOX 655303

grounding and decoupling considerations

General practices should apply to the PCB design to limit high frequency transients and noise that are fed back

into the supply and reference lines. This requires that the supply and reference pins be sufficiently bypassed.

In most cases 0.1-

µF ceramic chip capacitors are adequate to keep the impedance low over a wide frequency

range. Since their effectiveness depends largely on the proximity to the individual supply pin, they should be

placed as close to the supply pins as possible.

To reduce high frequency and noise coupling, it is highly recommended that digital and analog grounds be

shorted immediately outside the package. This can be accomplished by running a low impedance line between

DGND and AGND under the package.

TLV1571/78

100 nF

DGND

DVDD

AVDD

AGND

REFP

REFM

100 nF

100 nF

VREFP

VREFM

AVDD

DVDD

Figure 9. Placement for Decoupling Capacitors

power supply ground layout

Printed-circuit boards that use separate analog and digital ground planes offer the best system performance.

Wire-wrap boards do not perform well and should not be used. The two ground planes should be connected

together at the low-impedance power-supply source. The best ground connection may be achieved by

connecting the ADC AGND terminal to the system analog ground plane making sure that analog ground

currents are well managed.

Rs

Ri(MUX)

VS

VC

15 pF

Driving Source†

TLV1571/78

Ci

VI

VI = Input Voltage at AIN

VS = External Driving Source Voltage

Rs = Source Resistance

Ri(ADC)= Input Resistance of ADC

Ri(MUX)= Input Resistance (MUX on resistance)

Ci = Input Capacitance

VC= Capacitance Charging Voltage

† Driving source requirements:

• Noise and distortion for the source must be equivalent to the resolution of the converter.

• Rs must be real at the input frequency.

Ri(ADC)

MO

AIN

Figure 10. Equivalent Input Circuit Including the Driving Source