TPS546D24A: Output Current Measurement of TPS546D24A?

Louis Han15 

1) How does the output current measurement inside the TPS546D24A work?

The READ_IOUT current telemetry system uses a (Peak + Valley) / 2 current sense circuit which captures the peak inductor current by sampling the voltage drop across the integrated low-side FET 100ns after the turn-on of the low-side FET and the valley current 100ns before the turn-off of the low-side FET.  The sensed voltages are then averaged and process and temperature compensated using an on-die co-processed reference transistor driven to the same gate voltage as the low-side FET.

The cycle by cycle samples are then amplified to produce a 6.155mV/A current sense signal, which is then averaged over the ADC sample period, which depends on the selected ADC resolution set in the MISC_OPTIONS command.  Multiple samples are then filtered with a rolling average filter, with the number of averaged samples set by the averaging options in the TELEMETRY_CONFIG command.

2) Can the performance of the output current measurement accuracy be improved

Yes, the TPS546D24A provides IOUT_CAL_GAIN and IOUT_CAL_OFFSET commands to allow users to trim the READ_IOUT function in circuit, post assemble.  The recommended procedure is:

1) Power up the TPS546D24A and enable the output. (A low output voltage can be used to minimize leakage currents)

2) Draw a known reference current (IOUT1) from the output.

3) Wait >10ms for READ_IOUT averaging to complete

4) use READ_IOUT to read out the measured current and record it as READ_IOUT1

5) Draw a different known reference current (IOUT2) from the output

6) Wait >10ms for READ_IOUT averaging to complete

7) use READ_IOUT to read out the measured current and record it as READ_IOUT2

8) Program IOUT_CAL_GAIN using LINEAR11 data format  (Bits [15:11] use signed 2's compliment encoding to set the exponent from -16 to +15) Bits [10:0 use signed 2's compliment encoding to set the mantissa from -1024 to +1023)

IOUT_CAL_GAIN = (IOUT2 - IOUT1) / (READ_IOUT2 - READ_IOUT1)   (This is inverted from the typical IOUT_CAL_GAIN, which sets the sense resistance)

9) After adjusting the IOUT_CAL_GAIN, Draw a known reference current from the output (IOUT3, which can be equal a new current, or equal to IOUT1 or IOUT2

10) Wait >10ms for the READ_IOUT averaging to complete

11) use READ_IOUT to read out the measured current and record it as READ_IOUT3

11) Program IOUT_CAL_OFFSET using LINEAR11 data format  (Bits [15:11] use signed 2's compliment encoding to set the exponent from -16 to +15) Bits [10:0 use signed 2's compliment encoding to set the mantissa from -1024 to +1023)

IOUT_CAL_OFFSET = IOUT3 - READ_IOUT3

3) In case of Over Current Fault, the Margin of Error is too large 

I am sorry that you feel this way.  The Over Current Fault and Over Current Warning limits are intended to provide protection to the TPS546D24A power stage and its power source in the event of a failure of the load and are typically sufficiently accurate to meet that purpose.