8.2.2 ADC Driver and Reference Buffer

Figure 8-7 shows the use of a TLVx365-Q1 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-Q1 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-Q1 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-Q1 provide the output drive and fast-

settling performance.

ADS7945

14-bit

2 MSPS

R

S

+

–

5 V

AVDD

DVDD

5 V

5 V

TLV365-Q1

+

–

C

CB

5 V

TLV365-Q1

VREF

R

FILT

C

FILT

+

–

5 V

OPA378

Reference

5 V

R

F

R

G

Z

OUT

Sensor

Figure 8-7. TLVx365-Q1 as a SAR ADC Driver

8.3 Power Supply Recommendations

The TLVx365-Q1 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-Q1, TLV2365-Q1

SBOSAB8B – JUNE 2023 – REVISED SEPTEMBER 2024

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