FN8389 datasheet(49/56 Pages) RENESAS

49 / 56 page

ISL28023

FN8389 Rev.6.03

Page 49 of 55

Oct 27, 2022

The external clock pin can accept signal frequencies above

25MHz by programming the system clock frequency such that

the internal clock frequency is below 25MHz.

Figure 116 illustrates the effects of dividing the external clock

frequency on the VSHUNT measurement accuracy.

Figures 115 and 116 were generated by applying a DC voltage to

the VSHUNT input and measuring the signal by way of an ADC

conversion.

Overranging

It is not recommended to operate the ISL28023 outside the set

voltage range. In the event of measuring a shunt voltage beyond

the maximum set range (80mV) and lower than the clamp

voltage of the protection diode (1V), the measured output

reading may be within the accepted range but will be incorrect.

Shunt Resistor Selection

In choosing a sense resistor, the following resistor parameters

need to be considered: the resistor value, resistor temperature

coefficient and resistor power rating.

The sense resistor value is a function of the full-scale voltage

drop across the shunt resistor and the maximum current

measured for the application. The maximum measurable range

for the VSHUNT input (VINP-VINM) of the ISL28023 is 80mV. The

ISL28023 allows the user to define a unique range other than

±80mV.

Once the voltage range for the input is chosen and the maximum

measurable current is known, the sense resistor value is

calculated using Equation 19.

In choosing a sense resistor, the sense resistor power rating

should be taken into consideration. The physical size of a sense

resistor is proportional to the power rating of the resistor. The

maximum power rating for the measurement system is

calculated as the Vshunt_range multiplied by the maximum

measurable current expected. The power rating equation is

represented in Equation 20.

A general rule of thumb is to multiply the power rating calculated

in Equation 20 by 2. This allows the sense resistor to survive an

event when the current passing through the shunt resistor is

greater than the measurable maximum current. The higher the

ratio between the power rating of the chosen sense resistor and

the calculated power rating of the system (Equation 20), the less

the resistor will heat up in high current applications.

The Temperature Coefficient (TC) of the sense resistor directly

degrades the current measurement accuracy. The surrounding

temperature of the sense resistor and the power dissipated by

the resistor will cause the sense resistor value to change. The

change in resistor temperature with respect to the amount of

current that flows through the resistor is directly proportional to

the ratio of the power rating of the resistor versus the power

being dissipated. A change in sense resistor temperature results

in a change in sense resistor value. Overall, the change in sense

resistor value contributes to the measurement accuracy for the

system. The change in a resistor value due to a temperature rise

can be calculated using Equation 21.

Temperature is the change in temperature in Celsius. RsenseTC

is the temperature coefficient rating for a sense resistor. Rsense

is the resistance value of the sense resistor at the initial

temperature.

Table 50 is a shunt resistor look up table for select full-scale

current measurement ranges (ImeasMax). Table 50 also provides

the minimum rating for each shunt resistor.

It is often hard to readily purchase shunt resistor values for a

desired measurable current range. Either the value of the shunt

resistor does not exist or the power rating of the shunt resistor is

too low. A means of circumventing the problem is to use two or

FIGURE 116. EXTERNAL CLOCK vs EXTERNAL BIT VALUE

-8.5

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

0 12345

6789 10 11 12 13 14 15 16

ExtClkDiv BIT VALUE

ExtClk FREQUENCY = 45MHz

(EQ. 19)

R sense

V shunt_range

Imeas Max

TABLE 50. SHUNT RESISTOR VALUES AND POWER RATINGS FOR

SELECT MEASURABLE CURRENT RANGES

RSENSE/PRATING

VSHUNT RANGE (PGA SETTING)

ImeasMax

80mV

100µA

800Ω/8µW

1mA

80Ω/80µW

10mA

8Ω/800µW

100mA

800mΩ/8mW

500mA

160mΩ/40mW

80mΩ/80mW

16mΩ/400mW

10A

8mΩ/800mW

50A

1.6mΩ/4W

100A

0.8mΩ/8W

500A

0.16mΩ/40W

(EQ. 20)

P res_rating Vshunt_range Imeas Max



(EQ. 21)

R sense R sense Rsense TC

Temperature



FN8389 bảng dữ liệu(PDF) 49 Page - Renesas Technology Corp

FN8389 bảng dữ liệu(HTML) 49 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

bảng dữ liệu tải về

Link URL