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dc1748af

DEMO MANUAL DC1748A

OPERATING PRINCIPLES

Figure 1. DC1748 Radiated Emissions

EMI performance is shown in Figure 1, measured using

a Gigahertz Transverse Electromagnetic (GTEM) cell and

method detailed in IEC 61000-4-20, “Testing and Mea-

surement Techniques – Emission and Immunity Testing

in Transverse Electromagnetic Waveguides”.

The demo circuit includes provisions for programming

the three output voltage rails. Resistors R5, R6, and R7

allow the V+, V–, and VCC2 power rails, respectively, to

be reduced from their nominal operating voltages. The

formulas presented in Table 3 allow selection of the ap-

propriate resistor values.

Table 3.

VOLTAGE RAIL

RESISTOR TO REDUCE OUTPUT

V+

R5 = 150k • (V+ – 1.22)/(12.5 – V+)

V–

R6 = 150k • (1.22 + V–)/(–12.5 – V–)

VCC2

R7 = 110k • (VCC2 – 0.6)/(5 – VCC2)

FREQUENCY (MHz)

0

–30

–20

0

10

20

600 700 800 900

60

DC1748A F01

–10

100 200 300 400 500

1000

30

40

50

DETECTOR = QuasiPeak

RBW = 120kHz

VBW = 300kHz

SWEEP TIME = 17s

# OF POINTS = 501

DC1748A-A

DC1748A-B

CISPR 22 CLASS B LIMIT