TPS4812-Q1: Field-Adjustable Current Limits

Charles Gervais-Dumont

Part Number: TPS4812-Q1

Tool/software:

Hello,

We are designing an electronic circuit breaker using the nicely featured TPS4812-Q1.

We would need some current limit adjustments in the field, using digital potentiometers or some other means. Some questions arise when trying to meet all of the requirements laid out in the datasheet:

Is the <100uA limit for the I2t Current a hard limit? Will it simply be clamped if the Scaling Factor K is off?
Can the IMON Scaling Resistors Rset be higher than 500ohms? What drives this limit?
In Table 5-1, the datasheet mentions that the IOC pin can be driven by an MCU. How is this intended to be done?

Thank you,

7 months ago

0 Sarah Raines 7 months ago

TI__Expert 8820 points

Hi Charles,

Im working on this now and will get back to you tomorrow.

Thank you,

Sarah

0 Sarah Raines 7 months ago in reply to Sarah Raines

TI__Expert 8820 points

Hi Charles,

The 100 uA is driven by the range of our integrated I2T multiplier. If this is exceeded then it could cause the internal rail to droop and result in poor I2T accuracy.
The RSET limitation is based on the internal comparator limitation. Lower values typically are more susceptible to noise. Higher values might have more power consumption so we typically aim for something in the middle.
The RIOC value is used to "generate" a voltage value that can be compared internally. An MCU can just drive this voltage instead or theoretically make the IOC more configurable. Let me double check on this one.

Thank you,

Sarah

0 Sarah Raines 7 months ago in reply to Sarah Raines

TI__Expert 8820 points

Hi Charles,

Just confirming #3 is correct. Let me know if I can help further.

Thank you,

Sarah

0 Charles Gervais-Dumont 7 months ago in reply to Sarah Raines

Prodigy 10 points

Thank you Sarah. Is it possible to get some hint on how the voltage injected on the IOC pin with a DAC would affect the Overcurrent limit, based on the sense resistor and the Rset scaling resistors?

0 Sarah Raines 7 months ago in reply to Charles Gervais-Dumont

TI__Expert 8820 points

Hi Charles,

I see. You just need to determine the voltage you need to compare against the V_SNS-_SCP. Essentially the RSET and RSNS are the sensing values and the RIOC is the actual trip point used by the comparator to set over current threshold.

Thank you,

Sarah

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TPS4812-Q1: Field-Adjustable Current Limits