Why is the output voltage of the ADR3650A outside the expected range?

Hi Sebastien,

Thanks for reaching out. To clarify, are the parts that are sitting outside the specified range always the same parts, and are they always outside the range? Are they always >5.004V, or are you seeing units at <4.996V as well?

You also mentioned having difficulty reproducing this--are you saying these previously outside-of-range parts end up back in spec when they are powered-on again?

Hi, 

Yes, the components that do not meet the specifications are always the same (once identified). And when they fall outside the range (>5.004V), each one has its own specific value, for example: one is always at 5.021V, another at 5.014V, and so on. When these components are not faulty, they read 4.999V. No component has fallen below the range <4.996V. The problem always occurs above 5.004V.
The problem occurs occasionally after the power supply is switched on. When the problem occurs on certain ADR3650s, the Vref voltages remain stable at their incorrect value. If the power is switched off and on again, the Vref voltage may reset correctly (4.999V).
Please note that our product is equipped with 25 circuits containing an ADC and the ADR3650 Vref. Most of the time, the power supplies start up correctly. The problem occurs approximately once in ten cases and affects 10% of the ICs installed. (I can move the ADC circuits to my main board; the problem follows the ADC circuit and is not specific to the placement of the ADC circuit within the product).

Hi, 

Yes, the components that do not meet the specifications are always the same (once identified). And when they fall outside the range (>5.004V), each one has its own specific value, for example: one is always at 5.021V, another at 5.014V, and so on. When these components are not faulty, they read 4.999V. No component has fallen below the range <4.996V. The problem always occurs above 5.004V.
The problem occurs occasionally after the power supply is switched on. When the problem occurs on certain ADR3650s, the Vref voltages remain stable at their incorrect value. If the power is switched off and on again, the Vref voltage may reset correctly (4.999V).
Please note that our product is equipped with 25 circuits containing an ADC and the ADR3650 Vref. Most of the time, the power supplies start up correctly. The problem occurs approximately once in ten cases and affects 10% of the ICs installed. (I can move the ADC circuits to my main board; the problem follows the ADC circuit and is not specific to the placement of the ADC circuit within the product).

Hi Sebastien,

Thanks for the additional info. Have you been able to reproduce this with a faster power supply start up? 700ms does seem slow. Are you using the fast-startup functionality on the LT3045? The PGFB pin can be configured with Rpg1/Rpg2 to greatly increase supply startup times.