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Original question:

TIDA-00528: Some questions regarding the reference design.

TIDA-00528: INA226

Ray
Prodigy 170 points

Part Number: TIDA-00528
Other Parts Discussed in Thread: INA226

Document #: TIDU849 - November 2015

1. Page 8, equation (8), it gives a PFET current of 8mA. which will result in a Vsense of 80mV (equation 9).  Where did the 8mA/80mV come from?  I do not see them mentioned anywhere before equation 8.

2. What is the limiting value of Vsense?  The INA226 has a resolution of 1.25mV/bit.  With a full range voltage of 80mV, this gives you only 64 bits of data.  Could the range of the INA226 be increased by increasing the MAX Vsense?

  • 0
    TI__Mastermind 25765 points

    Ray, 

    Thanks for using E2E!

    1. The 80mV listed in the equation comes from the full scale input current range of the INA226. The full range is actually 81.92mV, but the designer chose 80mV for both mathematic ease as well as a small margin to prevent the device from topping out on its range. As this is the maximum potential sense voltage to be developed, and R2 and R1 are matched, the maximum worst case current that could be developed in the PFET is 8mA as equation 9 shows. 

    2. The disconnect here is there are separate values for current LSB and VBUS are separate values to measure the current and the bus voltage respectively. The 1.25mV/LSB you report here is actually for the bus voltage, while the current LSB for the INA226 is 2.5uV/LSB, which is the limiting factor of Vsense. This can be found in the INA226 datasheet: