9042 Datasheet, PDF(23/26 Page) Maxwell Technologies

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9042 Datasheet, PDF (23/26 Pages) Maxwell Technologies – 12-Bit, 41 MSPS A/D Converter

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12-Bit, 41 MSPS A/D Converter

9042

Power Supplies

Care should be taken when selecting a power source. Linear supplies are strongly recommended as switching sup-

plies tend to have radiated components that may be âreceivedâ by the 9042. Each of the power supply pins should be

decoupled as closely to the package as possible using 0.1 mF chip capacitors. The 9042 has separate digital and ana-

log +5 V pins. The analog supplies and the denoted AVCC digital supply pins are denoted DVCC. Although analog and

digital supplies may be tied together, best performance is achieved when the supplies are separate. This is because

the fast digital output swings can couple switching noise back into the analog supplies. Note that AVCC must be held

within 5% of 5 volts, however the DVCC supply may be varied according to output digital logic family (i.e., DVCC should

be connected to the supply for the digital circuitry).

Output Loading

Care must be taken when designing the data receivers for the AD9042. It is recommended that the digital outputs

drive a series resistor of 499 ohms followed by a CMOS gate like the 74AC574. To minimize capacitive loading, there

should only be one gate on each output pin. The digital outputs of the 9042 have a unique constant slew rate output

stage. The output slew rate is about 1 V/ns independent of output loading. A typical CMOS gate combined with PCB

trace and through hole will have a load of approximately 10 pF. Therefore as each bit switches, 10 mA

of dynamic current per bit will flow in or out of the device. A full- scale transition can cause up to 120 mA (12bits Â´ 10

mA/bit) of current to flow through the digital output stage. The series resistor will minimize the output currents that can

flow in the output stage. These switching currents are confined between ground and the DVCC pin. Standard TTL gates

should be avoided since they can appreciably add to the dynamic switching currents of the 9042.

01.07.05 REV 7

All data sheets are subject to change without notice 23

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