ADUM3471ARSZ datasheet(27/32 Pages) AD

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ADuM3470/ADuM3471/ADuM3472/ADuM3473/ADuM3474

Rev. 0 | Page 27 of 32

Table 18. Transformer Reference Designs

Part No.

Manufacturer

Turns Ratio,

PRI:SEC

ET Constant

(V × μs Min)

Total Primary

Inductance (μH)

Total Primary

Resistance (Ω)

Isolation

Voltage (rms)

Isolation

Type

Reference

JA4631-BL

Coilcraft

1CT:2CT

255

0.2

2500

Basic

Figure 38

JA4650-BL

Coilcraft

1CT:3CT

255

0.2

2500

Basic

Figure 39

KA4976-AL

Coilcraft

1CT:5CT

255

0.2

2500

Basic

Figure 40

TGSAD-260V6LF

Halo Electronics

1CT:2CT

389

0.8

2500

Supplemental

Figure 38

TGSAD-290V6LF

Halo Electronics

1CT:3CT

389

0.8

2500

Supplemental

Figure 39

TGSAD-292V6LF

Halo Electronics

1CT:5CT

389

0.8

2500

Supplemental

Figure 40

TGAD-260NARL

Halo Electronics

1CT:2CT

389

0.8

1500

Functional

Figure 38

TGAD-290NARL

Halo Electronics

1CT:3CT

389

0.8

1500

Functional

Figure 39

TGAD-292NARL

Halo Electronics

1CT:5CT

389

0.8

1500

Functional

Figure 40

TRANSFORMER ISOLATION VOLTAGE

Isolation voltage and isolation type should be determined for

the requirements of the application and then specified. The

transformers in Table 18 have been specified for 2500 V rms

for supplemental or basic isolation and for 1500 V rms functional

isolation. Other isolation levels and isolation voltages can be

specified and requested from the manufacturers in Table 18

or from other manufacturers.

SWITCHING FREQUENCY

The ADuM347x switching frequency can be adjusted from

200 kHz to 1 MHz by changing the value of the ROC resistor

shown in Figure 38, Figure 39, and Figure 40. The value of the

ROC resistor needed for the desired switching frequency can be

determined from the switching frequency vs. ROC resistance

curve shown in Figure 9. The output filter inductor value and

output capacitor value for the ADuM347x application schematics

have been designed to be stable over the switching frequency

range from 500 kHz to 1 MHz, when loaded from 10% to 90%

of the maximum load.

The ADuM347x also has an open-loop mode where the output

voltage is not regulated and is dependent on the transformer

turns ratio, NS/NP, and the conditions of the output including

output load current and the losses in the dc-to-dc converter

circuit. This open-loop mode is selected when the OC pin is

connected high to the VDD2 pin. In open-loop mode, the

switching frequency is 318 kHz.

TRANSIENT RESPONSE

The load transient response of the output voltage of the ADuM347x

for 10% to 90% of the full load is shown in Figure 30 to Figure 33

for the application schematics in Figure 38 and Figure 39. The

response shown is slow but stable and can have more output

change than desired for some applications. The output voltage

change with load transient has been reduced, and the output has

been shown to remain stable by adding more inductance to the

output circuits, as shown in the second VISO output waveform in

Figure 30 to Figure 33.

COMPONENT SELECTION

The ADuM347x digital isolators with 2 W dc-to-dc converters

require no external interface circuitry for the logic interfaces. Power

supply bypassing is required at the input and output supply pins.

Note that a low ESR ceramic bypass capacitor of 0.1 μF is required

on Side 1 between Pin 9 and Pin 10, and on Side 2 between Pin 18

and Pin 19, as close to the chip pads as possible.

The power supply section of the ADuM347x uses a high oscillator

frequency to efficiently pass power through the external power

transformer. In addition, normal operation of the data section

of the iCoupler introduces switching transients on the power

supply pins. Bypass capacitors are required for several operating

frequencies. Noise suppression requires a low inductance, high

frequency capacitor; ripple suppression and proper regulation

require a large value capacitor. To suppress noise and reduce ripple,

large-valued ceramic capacitors of X5R or X7R dielectric type are

recommended. The recommended capacitor value is 10 μF for

VDD1 and 47 μF for VISO. These capacitors have a low ESR and are

available in moderate 1206 or 1210 sizes for voltages up to 10 V. For

output voltages larger than 10 V, two 22 μF ceramic capacitors can

be used in parallel. See Table 19 for recommended components.

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