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LMP8603-Q1: Question about datasheet

Part Number: LMP8603-Q1
Other Parts Discussed in Thread: LMP8601-Q1, LMP8601, LMP8602-Q1, LMP8602, LMP8603,

Hi,

I am planning to use this part to monitor the current flowing into a negative power supply. While reading the datasheet, I am a bit confused by the following paragraph on page29 regarding Figure 63 in the data sheet (version: SNOSAR2H - revised APRIL 2016)

"If the load current of the battery is higher then the charging current, the output voltage of the LMP860x and LMP860x-

Q1 will be above the half offset voltage for a net current flowing out of the battery. When the charging current is
higher then the load current the output will be below this half offset voltage."

I would think when a net current flowing out of the battery, then +IN (Vp) < -IN(Vn) in Figure 63 and the LMP860x-Q1 output would be below the half offset voltage. 

Otherwise, this paragraph appears to contradict the paragraph on page 19 as

"Examples:
• LMP8601, LMP8601-Q1: A 5-V supply, a gain of 20x, OFFSET pin tied to VS, and a differential input signal of
10 mV results in 2.7 V at the output pin. Similarly, –10 mV at the input results in 2.3 V at the output pin.
• LMP8602, LMP8602-Q1: A 5-V supply, a gain of 50x, and a differential input signal of 10 mV results in 3.0 V
at the output pin. Similarly, –10 mV at the input results in 2.0 V at the output pin.
• LMP8603, LMP8603-Q1: A 5-V supply, a gain of 100x, and a differential input signal of 10 mV results in 3.5 V
at the output pin. Similarly, –10 mV at the input results in 1.5 V at the output pin.(1) (1)"

In addition to the above question, is there any other particular things I should consider or be aware when I use this to monitor the current flowing from a device to the negative power supply? 

Kind Regards,

John

  • Hello John,

    Thank you for the question, and welcome to the E2E forum! Our engineers will analyze and respond when we return to the office on Monday.

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • John,

    Thank you for using the forum for your concern. 

    You are correct that Section 8.2.3 has and editorial error.  Refer to the section on page 19 you highlighted.  I have taken note for the next datasheet revision.

    "Examples:
    • LMP8601, LMP8601-Q1: A 5-V supply, a gain of 20x, OFFSET pin tied to VS, and a differential input signal of
    10 mV results in 2.7 V at the output pin. Similarly, –10 mV at the input results in 2.3 V at the output pin.
    • LMP8602, LMP8602-Q1: A 5-V supply, a gain of 50x, and a differential input signal of 10 mV results in 3.0 V
    at the output pin. Similarly, –10 mV at the input results in 2.0 V at the output pin.
    • LMP8603, LMP8603-Q1: A 5-V supply, a gain of 100x, and a differential input signal of 10 mV results in 3.5 V
    at the output pin. Similarly, –10 mV at the input results in 1.5 V at the output pin.(1) (1)"

    Please be aware that the Common Mode range changes depending on the Supply voltage.  This will be more of a concern for you as you will be measuring the negative supply.  Also be aware of both the input impedance and how they differ depending on the VCM you are using.