AN2487

Electrical characteristics

17/32

4

Electrical characteristics

4.1

Test setup

Figure 7 shows a diagram of the loads and power supplies used for the test setup.

Figure 7.

Test setup

4.2

STHS4257 powered device interface controller

4.2.1

Signature current

Figure 8 compares the incremental slope and linearity of the signature resistance to the

ideal slope and the limits. The limiting resistances were plotted, and then the limiting

resistance curves and the data for the chip were shifted vertically to match the lower limit of

the measurement range. Error can then be measured at the upper end of the measurement

range.

Linearity of the slope does not appear to be an issue within the measurement range.

Figure 8.

Signature resistance slopes

R1

(2) 10 ohms 1%

R2

INPUT

AMMETER

TB1

TESTINPUT

TB2

DC OUTPUT

12V

VOLTMETER

3.3V

AMMETER

3.3V

VOLTMETER

12V

AMMETER

INPUT

VOLTMETER

DEVICE UNDER TEST

DC POWER SUPPLY 0-60V

DC LOAD 0-2A

DC LOAD 0-2A

12V LOAD

3.3V LOAD

S?

SW-SPST

Signature Current

0

100

200

300

400

500

600

024

68

10

12

Input Voltage

Shifted ST Data

Lower Resistance Limit

Upper Resistance Limit

Slope Measurement Range