ADP1034ACPZ-1-R7 datasheet(38/41 Pages) AD

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Data Sheet

ADP1034

APPLICATIONS INFORMATION

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Rev. 0 | 38 of 41

INSULATION LIFETIME

All insulation structures eventually break down when subjected to

voltage stress over a sufficiently long period. The rate of insulation

degradation is dependent on the characteristics of the voltage

waveform applied across the insulation as well as on the materials

and material interfaces.

The two types of insulation degradation of primary interest are

breakdown along surfaces exposed to the air and insulation wear

out. Surface breakdown is the phenomenon of surface tracking

and the primary determinant of surface creepage requirements in

system level standards. Insulation wear out is the phenomenon

where charge injection or displacement currents inside the insula-

tion material cause long-term insulation degradation.

Surface Tracking

Surface tracking is addressed in electrical safety standards by

setting a minimum surface creepage based on the working voltage,

the environmental conditions, and the properties of the insulation

material. Safety agencies perform characterization testing on the

surface insulation of components that allows the components to

be categorized in different material groups. Lower material group

ratings are more resistant to surface tracking. Therefore, lower ma-

terial group ratings provide adequate lifetime with smaller creepage.

The minimum creepage for a given working voltage and material

group is determined in each system level standard and is based

on the total rms voltage across the isolation, pollution degree, and

material group. The material group and creepage for the ADP1034

isolators are shown in Table 5.

Insulation Wear Out

The lifetime of insulation is determined by thickness, material prop-

erties, and the voltage stress applied. It is important to verify that

the product lifetime is adequate at the application working voltage.

The working voltage supported by an isolator for wear out may

not be the same as the working voltage supported for tracking.

The working voltage applicable to tracking is specified in most

standards.

Testing and modeling have shown that the primary driver of long-

term degradation is displacement current in the polyimide insula-

tion. This displacement current causes incremental damage to the

insulation. The stress on the insulation can be broken down into

broad categories: dc stress and ac component time varying voltage

stress. DC stress causes very little insulation wear out because

there is no displacement current. AC component time varying

voltage stress causes insulation wear out.

The ratings in certification documents are usually based on 60 Hz

sinusoidal stress because this reflects isolation from line voltage.

However, many practical applications have combinations of 60 Hz

ac and dc across the barrier as shown in Equation 1. Because only

the ac portion of the stress causes wear out, the equation can be

rearranged to solve for the ac rms voltage, as shown in Equation

2. For insulation wear out with the polyimide materials, the ac rms

voltage determines the product lifetime.

VRMS= VACRMS2+VDC2

(1)

VACRMS= VRMS2−VDC2

(2)

where:

VRMS is the total rms working voltage.

VAC RMS is the time varying portion of the working voltage.

VDC is the dc offset of the working voltage.

THERMAL ANALYSIS

For the purpose of thermal analysis, the ADP1034 die are treated

as a thermal unit, with the highest junction temperature reflected

in the θJA values from Table 8. The value of θJA is based on

measurements taken with the devices mounted on a JEDEC

standard, 4-layer board with fine width traces and still air. Under

normal operating conditions, the ADP1034 operates at a full load

across the full temperature range without derating the output cur-

rent. However, following the recommendations in the PCB Layout

Considerations section decreases thermal resistance to the PCB,

allowing increased thermal margins in high ambient temperatures.

Each switching regulator in the ADP1034 has a thermal shutdown

circuit that turns off the dc-to-dc converter and the outputs when a

die temperature of approximately 150°C is reached. When the die

cools below approximately 135°C, the ADP1034 dc-to-dc converter

outputs turn on again.

DETAILED TYPICAL APPLICATION CIRCUIT

Figure 89 shows a detailed typical application circuit for the

ADP1034.

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