8.2.2 ADC Driver and Reference Buffer

Figure 8-7 shows the use of a TLVx365 op amp as a SAR ADC input and reference pin driver. Sensors, which

are used for interfacing with the physical environment, exhibit high output impedance and cannot drive SAR ADC

inputs directly. The TLVx365 devices exhibit a very low-input bias current of 20 pA (maximum), and therefore do

not load these high-output impedance sensors. A wide-GBW amplifier connected to the output of these sensors

is needed to charge the switching capacitors at the SAR ADC input and to settle fast, to the required accuracy,

within the given acquisition time.

The ADC core draws transient current from the reference input during the conversion (digitization) phase,

which must be driven with a wide-GBW amplifier to offer fast settling and maintain a stable reference voltage

for excellent digitization performance. The TLVx365 reference buffer is used in a composite loop with the

OPA378 precision amplifier because of limitations in precision performance of wide-GBW amplifiers. The

precision amplifier maintains low-offset output, whereas the TLVx365 provide the output drive and fast-settling

performance.

ADS7945

14-bit

2 MSPS

R

S

+

–

5 V

AVDD

DVDD

5 V

5 V

TLV365

+

–

C

CB

5 V

TLV365

VREF

R

FILT

C

FILT

+

–

5 V

OPA378

Reference

5 V

R

F

R

G

Z

OUT

Sensor

Figure 8-7. TLVx365 as a SAR ADC Driver

8.3 Power Supply Recommendations

The TLVx365 family can be configured with unipolar supplies, split and symmetrical bipolar supplies (±2.5 V, for

example), or split and asymmetrical supplies (+4 V and –1 V, for example). The maximum permissible voltage,

VS, is 6 V.

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TLV365, TLV2365

SBOSAA8C – DECEMBER 2022 – REVISED AUGUST 2024

Copyright © 2024 Texas Instruments Incorporated

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