ADE1202 datasheet(27/42 Pages) AD

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Data Sheet

ADE1202

Rev. 0 | Page 27 of 42

The coefficients gi, where i = 0, 1, 2, … 15, are the coefficients of

the generating polynomial defined by the CRC-16-CCITT

algorithm as follows:

G(x) = x16 + x12 + x5 + 1

(9)

g0 = g5 = g12 = 1

(10)

All other gi coefficients are equal to 0.

FB(j) = aj − 1 XOR b15(j − 1)

(11)

b0(j) = FB(j) AND g0

(12)

bi(j) = FB(j) AND gi XOR bi − 1(j − 1), i = 1, 2, 3, … 15 (13)

Equation 11, Equation 12, and Equation 13 must be repeated for

j = 1, 2, … 16. The value written into the SPI communication CRC

contains Bit bi(16), where i = 0, 1, … 15.

PROTECTING THE INTEGRITY OF CONFIGURATION

REGISTERS

Configuration registers are either user accessible registers (R/W

registers listed in Table 17) or internal registers that are not user

accessible.

On power-up, the user accessible configuration registers can be

written without restriction.

When the registers are configured, write 0xADE1 to the LOCK

side to the nonisolated side. This action also disables write

access to the configuration registers from the SPI port to protect

the integrity of the configuration.

When the protection is enabled, read back the LOCK register to

ensure that Bit 0 (LOCK) was set to 1.

When the LOCK register is read, Bit 0 (LOCK) shows the

protection status. If the LOCK bit is 0, the protection is

disabled. If the LOCK bit is 1, the protection is enabled.

The lock function does not affect the ADDR_RELOAD bit, the

LOCK register, and the INT_STATUS register, which can all be

written when LOCK = 1.

To disable the register protection, write 0xADE0 to the LOCK

To change any configuration registers, disable the protection,

change the value of the register, and then reenable the protection.

VERSION

The REVID bits (Bits[8:5]) in the CTRL register identify the

version of the IC.

INSULATION WEAR OUT

The lifetime of insulation caused by wear out is determined by

the isolation thickness, material properties, 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 show that the primary driver of long-term

degradation is displacement current in the polyimide insulation

causing incremental damage. The stress on the insulation can be

broken down into broad categories, such as dc stress, which

causes very little wear out because there is no displacement

current, and an ac component time varying voltage stress,

which causes wear out.

The ratings in certification documents are typically based on

60 Hz sinusoidal stress because this value reflects isolation from

the line voltage. However, many practical applications have

combinations of 60 Hz ac and dc across the barrier, as shown

in Equation 14. 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 15. For insulation wear out with the

polyimide materials used in the ADE1202, the ac rms voltage

determines the product lifetime.

RMS

AC RMS

(14)

−

AC RMS

RMS

(15)

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.

Calculation and Use of Parameters Example

The following example frequently arises in power conversion

applications. Assume that the line voltage on one side of the

isolation is 240 V ac rms and a 400 V dc bus voltage is present

on the other side of the isolation barrier. The isolator material is

polyimide. To establish the critical voltages in determining the

creepage, clearance, and lifetime of a device, see Figure 47 and

the following equations.

TIME

VAC RMS

VRMS

VDC

VPEAK

Figure 47. Critical Voltage Example

Calculate the working voltage across the barrier from Equation 16

with the following equations:

RMS

AC RMS

(16)

240

400

RMS

(17)

In this example, VRMS = 466 V.

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