TPS53681 Datasheet, PDF (61/125 Pages) Texas Instruments – Dual-Channel (6-Phase + 2-Phase) or (5-Phase + 3-Phase) D-CAP+ Step-Down Multiphase Controller with NVM and PMBus

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TPS53681
SLUSCT1 – JUNE 2017
7.5.7 Output Current Sense and Calibration
The READ_IOUT command may be used to read the individual phase currents, and the total channel current.
7.5.7.1 Reading Individual Phase Currents
Using the PAGE and PHASE commands, the TPS53681 can be configured to return output current information
for each individual phase. The examples below demonstrate this process:
Example #1: Read back the output current of Channel A, First Phase
1. Select Channel A. Write PAGE to 00h
2. Select first phase. Write PHASE to 00h
3. Read READ_IOUT
Example #2: Read back the output current of Channel B, Second Phase
1. Select Channel B. Write PAGE to 01h
2. Select second phase. Write PHASE to 01h
3. Read READ_IOUT
7.5.7.1.1 Reading Total Current
When the PHASE command is set to 80h, the TPS53681 device is configured to return the total channel current
(sum of individual phase currents) in response to the READ_IOUT command.
Example: Read the Total Output Current of Channel A
1. Select Channel A. Write PAGE to 00h
2. Select total current measurement. Write PHASE to 80h
3. Read READ_IOUT
7.5.7.1.2 Calibrating Current Measurements
The IOUT_CAL_GAIN and IOUT_CAL_OFFSET commands are available to allow the user to fine-tune current
measurements. Setting the PHASE command to 80h also allows the total current measurement to be calibrated
in a similar manner. The TI power stage devices supply current information to the controller device, using the
CSPx and CSNx pins, with a scale of 5 mV/A. The IOUT_CAL_GAIN command may be used to fine-tune the
scaling inside the controller to account for any gain mismatch. Likewise, the IOUT_CAL_OFFSET command may
be used to apply an offset to the controller current measurements, to null offset errors.
Example: Calibrating Total Output Current Measurement
1. Select Channel A. Write PAGE to 00h
2. Select the total current. Write PHASE to 80h
3. First read back READ_IOUT under two known output currents:
(a) For this example, apply a load of 60 A
(b) Read back READ_IOUT, record the value. For this example, consider that READ_IOUT gives 59.0 A.
(c) For this example, apply a load of 120 A
(d) Read back READ_IOUT, record the value. For this example, consider that READ_IOUT gives 119.6 A
4. Calculate the gain error:
(a) The current reading increased (119.6 A - 59.0 A) = 60.6 A for a 60 A current step
(b) Hence, the current reading gain is (60.6 A / 60 A ) = 1.01.
(c) Ideally, the current reading gain is 1.00, so the readings show a +1% gain error.
5. Apply IOUT_CAL_GAIN to correct the gain error:
(a) The gain error is +1%, and the nominal current sense gain is 5 mΩ, so the current sense gain must be
lowered by 1%.
(b) Hence, the IOUT_CAL_GAIN should be programmed to 5 mΩ × (1-1%) = 4.95 mΩ
(c) Referring to Table 21 the closest acceptable value is 4.953125 mΩ, or D13Dh.
(d) Write IOUT_CAL_GAIN to D13Dh.
6. Determine the offset error at a given point:
(a) Apply a known load. In this example, 90 A.
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