ADUM3471ARSZ datasheet(28/32 Pages) AD

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ADuM3470/ADuM3471/ADuM3472/ADuM3473/ADuM3474

Rev. 0 | Page 28 of 32

Inductors must be selected based on the value and supply current

needed. Most applications with switching frequencies between

500 kHz and 1 MHz and load transients between 10% and 90%

of full load are stable with the 47 μH inductor value listed in Table 19.

Values as large as 200 μH can be used for power supply applications

with a switching frequency as low as 200 kHz to help stabilize the

output voltage or for improved load transient response (see Figure 30

to Figure 33). Inductors in a small 1212 or 1210 size are listed in

Table 19 with a 47 μH value and a 0.41 A current rating to handle the

majority of applications below a 400 mA load, and with a 100 μH

value and a 0.34 A current rating to handle a load to 300 mA.

Schottky diodes are recommended for their low forward voltage

to reduce losses and their high reverse voltage of up to 40 V to

withstand the peak voltages available in the doubling circuit

shown in Figure 39 and Figure 40.

Table 19. Recommended Components

Part Number

Manufacturer

Value

GRM32ER71A476KE15L

Murata

47 μF, 10 V, X7R,

1210

GRM32ER71C226KEA8L

Murata

22 μF, 16 V, X7R,

1210

GRM31CR71A106KA01L

Murata

10 μF, 10 V, X7R,

1206

MBR0540T1-D

ON Semiconductor

0.5 A, 40 V,

Schottky, SOD-123

LQH3NPN470MM0

Murata

47 μH, 0.41 A,

1212

ME3220-104KL

Coilcraft

100 μH, 0.34 A,

1210

PRINTED CIRCUIT BOARD (PCB) LAYOUT

Note that the total lead length between the ends of the low ESR

capacitor and the VDDx and GNDx pins must not exceed 2 mm.

Installing the bypass capacitor with traces more than 2 mm

in length can result in data corruption. See Figure 41 for the

recommended PCB layout.

GND1

VDD1

VREG

GND2

VDD2

VIA/VOA

VOA/VIA

VIB/VOB

VIC/VOC

VOB/VIB

VOC/VIC

VID/VOD

VDDA

VOD/VID

GND1

GND2

Figure 41. Recommended PCB Layout

In applications involving high common-mode transients, take

care to ensure that board coupling across the isolation barrier is

minimized. Furthermore, design the board layout such that

any coupling that does occur equally affects all pins on a given

component side. Failure to ensure this can cause voltage

differentials between pins, exceeding the absolute maximum

ratings specified in Table 10, thereby leading to latch-up and/or

permanent damage.

The ADuM347x are power devices that dissipate about 1 W of

power when fully loaded and running at maximum speed. Because

it is not possible to apply a heat sink to an isolation device, the

devices primarily depend on heat dissipation into the PCB through

the GND pins. If the devices are used at high ambient temperatures,

care must be taken to provide a thermal path from the GNDx

pins to the PCB ground plane. The board layout shows enlarged

pads for the GNDx pins (Pin 2 and Pin 10) on Side 1 and (Pin 11

and Pin 19) on Side 2. Large diameter vias should be implemented

from the pad to the ground planes and power planes to increase

thermal conductivity and to reduce inductance. Multiple vias in

the thermal pads can significantly reduce temperatures inside

the chip. The dimensions of the expanded pads are left to the

discretion of the designer and the available board space.

THERMAL ANALYSIS

The ADuM347x parts consist of two internal die attached to a

split lead frame with two die attach paddles. For the purposes of

thermal analysis, the die are treated as a thermal unit, with the

highest junction temperature reflected in the θJA from Table 5.

The value of θJA is based on measurements taken with the parts

mounted on a JEDEC standard, 4-layer board with fine width traces

and still air. Under normal operating conditions, the ADuM347x

devices operate at full load across the full temperature range

without derating the output current. However, following the

recommendations in the Printed Circuit Board (PCB) Layout

section decreases thermal resistance to the PCB, allowing

increased thermal margins in high ambient temperatures. The

ADuM347x has an thermal shutdown circuit that shuts down

the dc-to-dc converter and the outputs of the ADuM347x when

a die temperature of about 160°C is reached. When the die cools

below about 140°C, the ADuM347x dc-to-dc converter and

outputs turn on again.

PROPAGATION DELAY-RELATED PARAMETERS

Propagation delay is a parameter that describes the time it takes

a logic signal to propagate through a component (see Figure 42).

The propagation delay to a logic low output may differ from the

propagation delay to a logic high output.

INPUT (VIx)

OUTPUT (VOx)

tPLH

tPHL

50%

Figure 42. Propagation Delay Parameters

Pulse width distortion is the maximum difference between these

two propagation delay values and is an indication of how

accurately the input signal timing is preserved.

Channel-to-channel matching refers to the maximum amount

the propagation delay differs between channels within a single

ADuM347x component.

Propagation delay skew refers to the maximum amount the

propagation delay differs between multiple ADuM347x

components operating under the same conditions.

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