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Input Range

±10V

±5V

Without Trim

With Trim

(Adjust Gain)

+

+

+

+

AGND1

CAP

REF

AGND2

AGND1

CAP

REF

AGND2

2.2

µF

2.2

µF

2.2

µF

+5V

50k

Ω

576k

Ω

2.2

µF

+

+

AGND1

CAP

REF

AGND2

AGND1

CAP

REF

AGND2

+5V

+

+

2.2

µF

2.2

µF

576k

Ω

50k

Ω

2.2

µF

2.2

µF

ADS8519

SLAS462A – JUNE 2007 – REVISED MARCH 2008

Figure 30. Offset/Gain Circuits for Bipolar Input Ranges

AGND1. This referencing minimizes the ground-loop problem typical to analog designs. The analog input should

be driven by a low-impedance source. A typical driving circuit using the OPA627 or OPA132 is shown in

Figure 30.

The ADS8519 can operate with its internal 4.096V reference or an external reference. An external reference

connected to pin 6 (REF) bypasses the internal reference. The external reference must drive the 4k

Ω resistor

that separates pin 6 from the internal reference (see the illustration on page 1). The load varies with the

difference between the internal and external reference voltages. The external reference voltage can vary from

3.9V to 4.2V. The internal reference is approximately 4.096V. The reference, whether internal or external, is

buffered internally with the output on pin 5 (CAP).

The ADS8519 is factory-tested with 2.2

µF capacitors connected to pin 5 (CAP) and pin 6 (REF). Each capacitor

should be placed as close as possible to its pin. The capacitor on pin 6 band-limits the internal reference noise.

A smaller capacitor can be used, but it may degrade SNR and SINAD The capacitor on pin 5 stabilizes the

reference buffer and provides switching charge to the CDAC during conversion. Capacitors smaller than 1

µF

may cause the buffer to become unstable and not hold sufficient charge for the CDAC. The parts are tested to

specifications with 2.2

µF, so larger capacitors are not necessary. The equivalent series resistance (ESR) of

these compensation capacitors is also critical. Keep the total ESR under 3

Ω. See the Typical Characteristics

section concerning how ESR affects performance.

Copyright © 2007–2008, Texas Instruments Incorporated

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