LMP8602MASLASHNOPB datasheet(27/42 Pages) TI1

27 / 42 page

0.0

1.0

2.0

3.0

4.0

5.0

Load Current (A)

C001

VS = 5V

VS = 3.3V

RSENSE = 15mŸ

RSENSE =

VINMAX

ILOADMAX

10A

165 mV

16.5

PŸ

VINMAX =

VOUTMAX

Gain

3.3 V

20 V/V

= 165 mV

LMP8601, LMP8601-Q1

LMP8602, LMP8602-Q1

LMP8603, LMP8603-Q1

www.ti.com

SNOSAR2H – SEPTEMBER 2008 – REVISED APRIL 2016

Product Folder Links: LMP8601 LMP8601-Q1 LMP8602 LMP8602-Q1 LMP8603 LMP8603-Q1

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Typical Applications (continued)

8.2.1.1 Design Requirements

Using the circuit in Figure 60, the requirement is to measure coil current up to 10 A and drive the ADC input to a

maximum of 3.3 V. The OFFSET pin is grounded, so zero current will result in a zero volt output.

8.2.1.2 Detailed Design Procedure

First, the value of RSENSE must be determined. RSENSE can be found by dividing the maximum desired output

swing by the gain to determine the maximum input voltage. In this example, the LMP8601 is used, with a gain of

20 V/V, as shown in Equation 33:

(33)

Knowing 165 mV must be generated, the ideal value of the sense resistor can be determined through simple

ohms law:

(34)

The ideal sense resistor value is 16.5 m

Ω. The closest standard value is 15 mΩ, but this value may cause the

output to slightly overrange at 10 V. It is recommended to reduce the expected maximum output by a few percent

to allow for overloads and component tolerances. The next most popular values would be 10 m

Ω, 15 mΩ, and 20

Ω. 10 mΩ allows for a maximum output of 2 V at 10 A, but may be too low and not use the full output range. 20

Ω provides more sensitivity, but limits the maximum current to 8.25 A. 15 mΩ is a good compromise at 11 A

maximum, and allows for some component tolerance variation.

If a suitable sense resistor value is not available, it is possible to adjust the gain as detailed in the Gain

Adjustment section.

The sense resistor does dissipates power, so the maximum wattage rating and appropriate power deratings must

be observed. In the example above, the sense resistor dissipates 0.165 V × 10 A = 1.65 W, so a sense resistor

of at least twice the maximum expected power should be used (greater than 4 W).

8.2.1.3 Application Curve

Below is the expected output value using a 15-m

Ω sense resistor.

Figure 61. Expected Output Voltage vs Load Current Using 15-m

Ω Sense Resistor

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