TPS546D24A: Measured current by READ_IOUT command(8Ch)

Shunsuke Yamamoto

Part Number: TPS546D24A

Tool/software:

Hi team,

My customer has been designing the circuit with TPS546D24A, and has a question regarding PMBus function. My customer would like to measure the output current of TPS546D24A to measure the power consumption of the subsequent circuit by using READ_IOUT command(8Ch) on PMBus function. The inductor current is a sawtooth waveform, so my customer doesn't know the output value of this command is average current, peak current or valley current. Or other current? Please kindly let me know.

Best regards,

Shunsuke Yamamoto

3 months ago

0 Shunsuke Yamamoto 3 months ago

TI__Expert 7811 points

Hi team,

I got an additional question. Could you please kindly help me to answer?

My customer would like to know the output format of READ_OUT command. Does it follow " 7.3. LENEAR11 Numeric Format on PMBus Power System Management Protocol Specification Part II – Command Language?

https://urldefense.com/v3/__https://pmbusprod.wpenginepowered.com/wp-content/uploads/2022/01/PMBus-Specification-Rev-1-3-1-Part-II-20150313.pdf__;!!G3vK!Q7iuBcwbxFZz3mi6XMId4CPRDq4zGosU23PElTgeb4gBT7EZbIaO3MesMWm190fwrl0__2dgVRX8RZK_yMfUQQQ$

Best regards,

Shunsuke Yamamoto

0 Tomoya Ide 3 months ago in reply to Shunsuke Yamamoto

TI__Genius 11396 points

Hi Shunsuke,

The READ_IOUT output value is the average current, not peak or valley.

Command 8C (READ_IOUT) uses the data format "SLINEAR11" Where the 16-bit word is separated into 2 two's compliment signed values.

Bits 15:11 provide the exponent value in 2s compliment encoding, supporting values from -16 to +15.

Bits 10:0 provide the Mantissa in two's complement signed values from -1024 to +1023

You will likely need a translation function to convert from SLINEAR11 to a floating point value. It is important that the translation function recognize signed Mantissa values or small negative current values will be reported as extremely large positive currents.

Here is an article on translating SLINEAR11 values into floating point values - https://embeddedartistry.com/blog/2018/07/05/linear11-conversion-using-a-sign-extension-bit-twiddling-hack/

Thank you,
Tomoya

0 Shunsuke Yamamoto 3 months ago in reply to Tomoya Ide

TI__Expert 7811 points

Hi Tomoya,

Thank you for the support. The average current means the middle of the sawtooth waveform of the inductor current. Is my understanding correct?

Best regards,

Shunsuke Yamamoto

+1 Tomoya Ide 3 months ago in reply to Shunsuke Yamamoto

TI__Genius 11396 points

Hi Shunsuke,

You can say it is 'middle' of the inductor current waveform. The description of the current sense telemetry is in the datasheet. It senses the low-side FET current at the start and end of each low-side FET on-time and averages the two measurements to monitor the average inductor current.

Thank you,
Tomoya

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TPS546D24A: Measured current by READ_IOUT command(8Ch)