SLAS989D January 2014 – October 2017 ADC12J4000
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 ADC12J4000 device 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 ADC12J4000 device. If not a dedicated supply, the ADC supplies must be the same supply used for other analog circuitry.
The ADC12J4000 device is 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 ADC12J4000 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 ADC12J4000 device. 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 ADC12J4000 device, 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.