OPA607 datasheet(28/48 Pages) TI

28 / 48 page

tR (10% to 90%) = 0.35 Hz / BW

(3)

For an ADC like ADS7042 running at a sampling rate of 500 kSPS of a clock of 12.5 MHz, the effective

bandwidth of the op amp required to drive such an ADC is approximately 2.7 MHz. See the TI precision lab

videos on driving SAR ADCs to understand the underlying calculation. The OPAx607 has a GBW of 50 MHz.

With a gain of 20 V/V, the closed loop bandwidth turns out to approximately 2.5 MHz, making this device the

most suitable, cost-optimized amplifier for this application. The RC charge bucket (240 Ω and 688 pF in Figure

9-12) designed at the input of the SAR ADC is derived from the calculations provided in the SAR ADC precision

lab videos. The fundamental concept behind the design of this charge bucket filter is to ensure that the sample

and hold capacitor is charged to the required final voltage within the acquisition window of the ADC.

As shown in Figure 9-14, a DC accuracy of higher than 0.05% is achieved with the OPAx607. The simulations

are captured with and without voltage offset calibration. Frequency response shown in Figure 9-13 indicate

different signal bandwidth at VOUT, VADC and with and without CF of 220 pF.

9.2.4.3 Application Curves

Frequency (Hz)

-30

-24

-18

-12

-6

100

10k

100k

10M

100M

D010

VADC

VOUT

VOUT , CF = 220 pF

Figure 9-13. Frequency Response of Low Side

Current Sensing

Current across RSH (A)

-20

-15

-10

-5

-2

-0.2

-1.2

-0.16

-0.4

-0.12

0.4

-0.08

1.2

-0.04

2.8

0.04

3.6

0.08

4.4

0.12

5.2

0.16

0.2

D003

Measured Output

Ideal Output

% Error w/o callibration

% Error with callibration

Figure 9-14. DC Current-Sense Transfer Function

OPA607, OPA2607

SBOS981J – OCTOBER 2019 – REVISED APRIL 2021

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