APPLICATION INFORMATION

50 W

50 W

20 pF

20 W

7 pF

VDD

IN

GND

Driving the VIN and VDD Pins

VDD

VIN

GND

CS

SDO

SCLK

10 nF

1 mF

VDD

VDD

VIN

GND

CS

SDO

SCLK

10nF

1 mF

GND

IN

OUT

3V/5V

1mF

5V/7V

REF5030/REF5050

ADS7883

www.ti.com ....................................................................................................................................................................................................... SLAS594 – JULY 2008

Figure 24. Typical Equivalent Sampling Circuit

The VIN input to the ADS7883 should be driven with a low impedance source. In most cases additional buffers

are not required. In cases where the source impedance exceeds 200

Ω, using a buffer would help achieve the

rated performance of the converter. The THS4031 is a good choice for the driver amplifier buffer.

The reference voltage for the ADS7883 A/D converter is derived from the supply voltage internally. The device

offers limited low-pass filtering functionality on-chip. The supply to these converters should be driven with a low

impedance source and should be decoupled to the ground. A 1-µF storage capacitor and a 10-nF decoupling

capacitor should be placed close to the device. Wide, low impedance traces should be used to connect the

capacitor to the pins of the device. The ADS7883 draws very little current from the supply lines. The supply line

can be driven by either:

• Directly from the system supply.

• A reference output from a low drift and low drop out reference voltage generator like the REF5030 or

REF5050. The ADS7883 can operate with a wide range of supply voltages. The actual choice of the

reference voltage generator depends upon the system. Figure 26 shows one possible application circuit.

• A low-pass filtered version of the system supply followed by a buffer like the zero-drift OPA735 can also be

used in cases where the system power supply is noisy. Care should be taken to ensure that the voltage at the

VDD input does not exceed 7 V (especially during power up) to avoid damage to the converter. This can be

done easily using single supply CMOS amplifiers like the OPA735. Figure 27 shows one possible application

circuit.

Figure 25. Supply/Reference Decoupling Capacitors

Figure 26. Using the REF5030/REF5050 Reference

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): ADS7883