ADS8028

430 pF

24.9

Ÿ

+

OPA836

VS+

VS+

AC

0V W 2.5V ADC

Input Range

ADS8028

www.ti.com

SBAS549B – MAY 2011 – REVISED MARCH 2012

APPLICATION INFORMATION

USAGE OF INTERNAL TEMPERATURE SENSOR

The ADS8028 accurately measures and converts the temperature of its own silicon die. Most of the heat transfer

between any external heat source and the ADS8028 die occurs via the thermal pad. Therefore, the ADS8028

can be used to measure the temperature of any external heat source by minimizing the thermal resistance

between the heat source and the device thermal pad.

APPLICATION CIRCUITS

ADC Driver

The OPA836 is a low-power, 205-MHz bandwidth op amp with 560-V/

μs slew rate, and is an excellent driver for

the ADS8028 SAR ADC for high ac performance at maximum throughput (1 MSPS). The high bandwidth of the

OPA836 is able to correct for fast load transients created by the SAR ADC switching behavior. An RC circuit

inserted between the OPA836 and ADS8028 is recommended to further aid the overall circuit performance. This

configuration is shown in Figure 40. The RC filter effectively limits the full-power bandwidth of the ADS8028 to

reduce the overall noise bandwidth and peak-to-peak noise sampled by the ADS8028. The capacitance is sized

to be 10 to 20 times larger than the internal ADS8028 sampling capacitor to provide quick charge sharing to the

ADC during switching transients. Furthermore, the resistor provides some isolation between the OPA836 output

and the capacitive load to stabilize the amplifier. The RC circuit –3-dB cutoff frequency should be an order of

magnitude or larger than the highest input signal frequency to avoid attenuating the desired input signal. A

collection of other ADC driving circuits can be found in application note Buffer Op Amp to ADC Circuit Collection

(SLOA098).

Figure 40. OPA836 Buffer

The TINA-TI simulation file of this circuit can be downloaded by clicking the following link: OPA836 Buffer.

Copyright © 2011–2012, Texas Instruments Incorporated

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Product Folder Link(s): ADS8028