OPA365 Datasheet, PDF(11/16 Page) Burr-Brown (TI) – 2.2V, 50MHz, Low-Noise, Single-Supply Rail-to-Rail OPERATIONAL AMPLIFIERS

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OPA365 Datasheet, PDF (11/16 Pages) Burr-Brown (TI) – 2.2V, 50MHz, Low-Noise, Single-Supply Rail-to-Rail OPERATIONAL AMPLIFIERS

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www.ti.com

One point to observe when considering the MFB filter

is that the output is inverted, relative to the input. If this

inversion is not required, or not desired, a noninverting

output can be achieved through one of these options:

1) adding an inverting amplifier; 2) adding an additional

2nd-order MFB stage; or 3) using a noninverting filter

topology such as the Sallen-Key (shown in Figure 9).

MFB and Sallen-Key, low-pass and high-pass filter syn-

thesis is quickly accomplished using TIâs FilterPro pro-

gram. This software is available as a free download at

www.ti.com.

DRIVING AN ANALOG-TO-DIGITAL CONVERTER

Very wide common-mode input range, rail-to-rail input

and output voltage capability and high speed make the

OPA365

OPA2365

SBOS365A â JUNE 2006 â REVISED JULY 2006

OPA365 an ideal driver for modern ADCs. Also, be-

cause it is free of the input offset transition characteris-

tics inherent to some rail-to-rail CMOS op amps, the

OPA365 provides low THD and excellent linearity

throughout the input voltage swing range.

Figure 10 shows the OPA365 driving an ADS8326,

16-bit, 500kSPS converter. The amplifier is connected

as a unity-gain, noninverting buffer and has an output

swing to 0V, making it directly compatible with the ADC

minus full-scale input level. The 0V level is achieved by

powering the OPA365 Vâ pin with a small negative volt-

age established by the diode forward voltage drop.

A small, signal-switching diode or Schottky diode

provides a suitable negative supply voltage of â0.3 to

â0.7V. The supply rail-to-rail is equal to V+, plus the

small negative voltage.

VIN = 1VRMS

1.8kâ¦

19.5kâ¦

150kâ¦

3.3nF

220pF

47pF

OPA365

VOUT

Figure 9. Configured as a 3-Pole, 20kHz, Sallen-Key Filter

+5V

V+

OPA365

100nF

R1(1)

100â¦

Vâ

VIN

0 to 4.096V

C3(1)

1nF

500â¦

â5V

Optional(2)

SD1

BAS40

100nF

+5V

REF3240

4.096V

+5V

+IN

ADS8326

16âBit

âIN 100kSPS

REF IN

100nF

NOTES: (1) Suggested value; may require adjustment based on specific application.

(2) Singleâsupply applications lose a small number of ADC codes near ground

due to op amp output swing limitation. If a negative power supply is available,

this simple circuit creates a â0.3V supply to allow output swing to true ground

potential.

Figure 10. Driving the ADS8326

▷