Part Number: TPS54318
Other Parts Discussed in Thread: IWRL6432,
Hi TI Support Team,
We are using a TI DC-DC buck regulator (TPS54318RTER) to generate a 1.8 V rail (rated 3 A) for powering a radar module (which uses IWRL6432 chipset from Texas Instruments).
Radar module spec for Min operating voltage and Max Current is below
During system-level testing, when the radar module is actively transmitting, we observe periodic voltage dips and overshoot on the 1.8 V rail. These events are correlated with the radar TX activity and appear to be load-induced transients rather than steady-state switching ripple.
Measurement summary:
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Nominal VOUT: 1.8 V
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Observed transient deviation:
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Undershoot: ~62 mV
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Overshoot: ~32 mV
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Total transient excursion: ~94 mV p-p
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We have also validated the regulator independently using an electronic load with a 0.2 A to 1.3 A load step at a slew rate of 0.025 A/µs, where we observed approximately 38 mV(Current steps 1.3A to 0.2A) and -50mV(Current step 0.2A to 1.3A transient deviation, indicating stable loop behavior.
The radar module datasheet specifies an operating supply range of 1.71 V to 1.89 V, so how we can measure minimum voltage out of below two case. since in case-2 we get minimum voltage is out of sepc from moduel minimum requirement.
Minimum Voltage =1.8V-Undershoot=1.8V-62mV=1.738V Case -1
Minimum Voltage =1.8V- Ripple (Undershoot+Overshoot)=1.8V-(62+32)=1.8V-94mV=1.706V Case -2
We would like your guidance on the following:
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How should such load-induced transient deviations be evaluated versus traditional ripple specifications?
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Should We measure ripple Transient + to Tarnsient -, in our case can we call our ripple is 94mV ( Addition of Undershoot: ~62 mV and Overshoot: ~32 mV).
- Or Ripple should be seperatly measure when load is get stable, in that case ripple we get 10-15mV with radar module (ignore Transiet part).
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From a regulator perspective, is this level of transient deviation considered acceptable for fast, pulsed loads?
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Are there any recommended PDN optimization or output capacitance guidelines (type, value, placement) to further reduce transient droop for high di/dt loads?
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When the module datasheet specifies a minimum operating voltage (for example, 1.71 V in this case), does this limit assume a steady-state DC voltage, or does it also account for short-duration transient voltage deviations?
Partial SCH below
Your inputs will help us determine whether the observed behavior is acceptable as-is or if further optimization is recommended.
Thank you for your support.
Best regards,
Kunal Barot
