ADS7038:Question about Input Current Spikes During Sampling in ADS7038

Daigo Kawaura

Part Number: ADS7038

Tool/software:

Dear TI Support Team,

I’m designing with the ADS7038 and have a concern about the instantaneous input current at the very beginning of the acquisition phase when the internal sampling capacitor is initially uncharged.

At the start of sampling, does the ADS7038 exhibit a brief inrush current into the sampling capacitor? If we take VIN = 3.3 V and use the datasheet’s sampling switch on‑resistance RSW ≈ 150 Ω, is it reasonable to estimate the initial current as
$I_{inrush} \approx \frac{V ^{I N}}{R ^{S W}} = \frac{3.3}{150} \approx 22 mA$ ?
If this estimate is valid, how should it be interpreted relative to the 10 mA absolute‑maximum pin current—must instantaneous events also remain <10 mA, or are very short‑duration transients accounted for and acceptable?
Are there recommended input network/driver practices (e.g., small series resistor with RC filter, acquisition‑time settings, or source‑impedance limits) to mitigate any adverse effects from this transient?

Thank you for your guidance.

Best regards,

20 hours ago

0 Joel Meraz 9 hours ago

TI__Genius 14880 points

Hi Daigo,

The 10mA limit is relevant while the AINx / GPOx pins are being overdriven. Per the abs max table, the minimum voltage the pins accept is GND – 0.3V, and the maximum is AVDD + 0.3V.

Operation below the minimum and above the maximum risks forward biasing internal ESD clamp diodes. In the case that the diodes are biased, current should be sufficiently limited as to not damage them. In this fault condition, even transient currents must be limited to below 10mA.

During normal operation within the input range, it is not a concern with a voltage source that is not normally forcing current. To avoid an overvoltage fault condition external clamp diodes are recommended.

Regards,
Joel

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ADS7038:Question about Input Current Spikes During Sampling in ADS7038