ADS7886 Datasheet, PDF (12/17 Pages) Texas Instruments – 12-Bit, 1-MSPS, MICRO-POWER, MINIATURE SAR ANALOG-TO-DIGITAL CONVERTERS

ADS7886
SLAS492 – SEPTEMBER 2005
APPLICATION INFORMATION
V_DD
60 W
IN
20 W
GND
60 W
16 pF
5 pF
Figure 28. Typical Equivalent Sampling Circuit
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Driving the VIN and V_DD Pins
The VIN input 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 A/D converter is derived from the supply voltage internally. The devices offer
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 ADS7886 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 REF3030 or REF3130.
The ADS7886 operates from a wide range of supply voltages. The actual choice of the reference voltage
generator would depend upon the system. Figure 30 shows one possible application circuit.
• A low-pass filtered 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 V_DD input
does not exceed 7 V to avoid damage to the converter. This can be done easily using single supply CMOS
amplifiers like the OPA735. Figure 31 shows one possible application circuit.
V_DD
1 mF 10 nF
V_DD
VIN
GND
CS
SDO
SCLK
Figure 29. Supply/Reference Decoupling Capacitors
5V
1 mF
REF3030
IN
OUT
GND
3V
1 mF 10 nF
V_DD
VIN
GND
CS
SDO
SCLK
Figure 30. Using the REF3030 Reference
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