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ADC12J1600 Datasheet(PDF) 87 Page - Texas Instruments |
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ADC12J1600 Datasheet(HTML) 87 Page - Texas Instruments |
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87 / 98 page  ADC12J1600, ADC12J2700 www.ti.com SLAS969C – JANUARY 2014 – REVISED JULY 2015 9 Power Supply Recommendations Data-converter-based systems draw sufficient transient current to corrupt their own power supplies if not adequately bypassed. A 10-µF capacitor must be placed within one inch (2.5 cm) of the device power pins for each supply voltage. A 0.1-µF capacitor must be placed as close as possible to each supply pin, preferably within 0.5 cm. Leadless chip capacitors are preferred due to their low-lead inductance. As is the case with all high-speed converters, the ADC12J1600 and ADC12J2700 devices must be assumed to have little power-supply noise-rejection. Any power supply used for digital circuitry in a system where a large amount of digital power is consumed must not be used to supply power to the ADC12J1600 and ADC12J2700 devices. If not a dedicated supply, the ADC supplies must be the same supply used for other analog circuitry. 9.1 Supply Voltage The ADC12J1600 and ADC12J2700 devices are specified to operate with nominal supply voltages of 1.9 V (VA19) and 1.2 V (VA12, VD12). For detailed information regarding the operating voltage minimums and maximums see the Recommended Operating Conditions table. During power-up the voltage on all 1.9-V supplies must always be equal to or greater than the voltage on the 1.2- V supplies. Similarly, during power-down, the voltage on the 1.2-V supplies must always be lower than or equal to that of the 1.9-V supplies. In general, supplying all 1.9-V buses from a single regulator, and all 1.2-V buses from a single regulator is the easiest method to ensure that the 1.9-V supplies are greater than the 1.2-V supplies. If the 1.2-V buses are generated from separate regulators, they must rise and fall together (within 200 mV). The voltage on a pin, including a transient basis, must not have a voltage that is in excess of the supply voltage or below ground by more than 150 mV. A pin voltage that is higher than the supply or that is below ground can be a problem during startup and shutdown of power. Ensure that the supplies to circuits driving any of the input pins, analog or digital, do not rise faster than the voltage at the ADC12J1600 and ADC12J2700 power pins. The values in the Absolute Maximum Ratings table must be strictly observed including during power up and power down. A power supply that produces a voltage spike at power turnon, turnoff, or both can destroy the ADC12J1600 and ADC12J2700 devices. Many linear regulators produce output spiking at power on unless there is a minimum load provided. Active devices draw very little current until the supply voltages reach a few hundred millivolts. The result can be a turn-on spike that destroys the ADC12J1600 and ADC12J2700 devices, unless a minimum load is provided for the supply. A 100- Ω resistor at the regulator output provides a minimum output current during power up to ensure that no turn-on spiking occurs. Whether a linear or switching regulator is used, TI recommends using a soft-start circuit to prevent overshoot of the supply. 10 Layout 10.1 Layout Guidelines Proper grounding and proper routing of all signals is essential to ensure accurate conversion. Each ground layer should be a single unified ground plane, rather than splitting the ground planes into analog and digital areas. Because digital switching transients are composed largely of high frequency components, the skin effect dictates that the total ground-plane copper weight has little effect upon the logic-generated noise. Total surface area is more important than the total ground-plane volume. Coupling between the typically-noisy digital circuitry and the sensitive analog circuitry can lead to poor performance that can be impossible to isolate and remedy. The solution is to keep the analog circuitry well separated from the digital circuitry. High-power digital components must not be located on or near any linear component or power-supply trace or plane that services analog or mixed-signal components because the resulting common return current path could cause fluctuation in the analog input ground return of the ADC which causes excessive noise in the conversion result. In general, assume that analog and digital lines must cross each other at 90° to avoid digital noise into the analog path. In high frequency systems, however, avoid crossing analog and digital lines altogether. The input clock lines must be isolated from all other lines, both analog and digital. The generally-accepted 90° crossing must be avoided because even a same amount of coupling causes problems at high frequencies. Best performance at high frequencies is obtained with a straight signal path. Copyright © 2014–2015, Texas Instruments Incorporated Submit Documentation Feedback 87 Product Folder Links: ADC12J1600 ADC12J2700 |
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