JAJSDD3B June 2017 – January 2019 TPS53681
PRODUCTION DATA.
The TPS53681 reports input current via an integrated current sense interface on the CSPIN and VIN_CSNIN pins. A conceptual block diagram is shown in Figure 22. This circuit must be calibrated to the value of the sense element, RSENSE (e.g. shunt resistance or DCR), chosen. The values of AIIN, IIN_MAX and IIN_OFS may be used to calibrate input current sensing. These settings are programmed using the MFR_SPECIFIC_10 and MFR_SPECIFIC_12 commands.
The IIN_RGAIN bits in MFR_SPECIFIC_12, and the IIN_GAIN_CTRL bit in MFR_SPECIFIC_10 select AIIN, the gain of the analog input current sense interface. Refer to Table 18 for a table of supported AIIN values. Note that the analog gain setting also corresponds to maximum allowed signal level and measured input current according to Table 14.
IIN_GAIN_CTRL
(MFR_SPECIFIC_10) |
IIN_RGAIN
(MFR_SPECIFIC_12) |
Effective AIIN | Maximum Supported
(CSPIN–VIN_CSNIN) Voltage |
Maximum Supported
Input Current Measurement |
---|---|---|---|---|
0b | 00b | 0.15 mΩ | 7.5 mV | 50.0 A |
0b | 01b | 0.25 mΩ | 12.5 mV | 50.0 A |
0b | 10b | 0.3 mΩ | 15.0 mV | 50.0 A |
0b | 11b | 0.5 mΩ | 25.0 mV | 50.0 A |
1b | 00b | 1.2 mΩ | 7.5 mV | 6.25 A |
1b | 01b | 2.0 mΩ | 12.5 mV | 6.25 A |
1b | 10b | 2.4 mΩ | 15.0 mV | 6.25 A |
1b | 11b | 4.0 mΩ | 25.0 mV | 6.25 A |
The IIN_MAX bits in MFR_SPECIFIC_10 may also be used to digitally calibrate the gain of the input current reporting. Changing IIN_MAX allows the user to achieve fine gain calibration of the input current sense circuit, as well as support sense element resistor values other than those directly supported using AIIN.
The nominal value of IIN_MAX is 50d. When the sense element resistance and AIIN are equal, IIN_MAX should remain set to 50d. Changing IIN_MAX adjusts the current sense gain ratiometrically with respect to the nominal value of 50d. For example, changing IIN_MAX to 25d, reduces the effective gain by a factor of 2, and changing IIN_MAX to 10d, reduces the effective gain by a factor of 5. IIN_MAX has a maximum value of 64d. When using a sense element RSENSE not equal to one of the supported AIIN values, the IIN_MAX register must be adjusted according to Equation 3 to achieve accurate gain calibration.
The IIN_OFS bits in MFR_SPECIFIC_10 may also be used to apply an offset to the sensed current in amperes.
Example #1: 0.5 mΩ RSENSE
With a 0.5 mΩ sense element value, for example, (VCSPIN - VVIN_CSNIN) = 10 mV corresponds to 20 A current. Select the analog interface gain, AIIN =0.5 mΩ, since this selection is available in Table 18, and do not apply any scaling via IIN_MAX (set it to 50d).
Example #2: 1.0 mΩ RSENSE
With a 1.0 mΩ sense element value, for example, (VCSPIN - VVIN_CSNIN) = 10 mV corresponds to 10 A current. With the analog interface gain, AIIN set to 0.5 mΩ, 10 mV would be interpreted as 20 A. Therefore apply IIN_MAX = 50*(0.5 mΩ / 1 mΩ) to reduce the effective gain by a factor of 2, so 10 mV is interpreted as 10 A.