ADM3052

Rev. 0 | Page 16 of 20

THERMAL SHUTDOWN

The ADM3052 contains thermal shutdown circuitry that protects

the part from excessive power dissipation during fault conditions.

Shorting the driver outputs to a low impedance source can result

in high driver currents. The thermal sensing circuitry detects the

increase in die temperature under this condition and disables the

driver outputs. This circuitry is designed to disable the driver

outputs when a junction temperature of 150°C is reached. As

the device cools, the drivers reenable at a temperature of 140°C.

LINEAR REGULATOR

11 V to 25 V) and regulates this voltage to 5 V to provide power

transceiver circuits). The linear regulator uses two regulation

loops to share the power dissipation between the internal die and

an external resistor. This reduces the internal heat dissipation in

the package. The 300 Ω external resistor should be capable of

dissipating 750 mW of power and have a tolerance of 1%.

MAGNETIC FIELD IMMUNITY

The limitation on the magnetic field immunity of the iCoupler

is set by the condition in which an induced voltage in the receiv-

ing coil of the transformer is large enough to either falsely set or

reset the decoder. The following analysis defines the conditions

under which this may occur. The 3 V operating condition of the

ADM3052 is examined because it represents the most susceptible

mode of operation.

The pulses at the transformer output have an amplitude greater

than 1 V. The decoder has a sensing threshold of about 0.5 V,

thus establishing a 0.5 V margin in which induced voltages can

be tolerated.

The voltage induced across the receiving coil is given by

⎟

⎠

⎞

⎜

⎝

⎛

β

−

=

2

n

r

dt

d

V

;

N

n

,

.

.

.

,

2

,

1

=

where:

β is the magnetic flux density (gauss).

N is the number of turns in the receiving coil.

Given the geometry of the receiving coil and an imposed

requirement that the induced voltage is, at most, 50% of the

0.5 V margin at the decoder, a maximum allowable magnetic

field can be determined using Figure 31.

MAGNETIC FIELD FREQUENCY (Hz)

1k

10k

100k

100M

1M

10M

100

10

1

0.1

0.01

0.001

Figure 31. Maximum Allowable External Magnetic Flux Density

For example, at a magnetic field frequency of 1 MHz, the

maximum allowable magnetic field of 0.2 kgauss induces a

voltage of 0.25 V at the receiving coil. This is about 50% of the

sensing threshold and does not cause a faulty output transition.

Similarly, if such an event occurs during a transmitted pulse and

is the worst-case polarity, it reduces the received pulse from

>1.0 V to 0.75 V, still well above the 0.5 V sensing threshold of

the decoder.

Figure 32 shows the magnetic flux density values in terms of

more familiar quantities, such as maximum allowable current

flow at given distances away from the ADM3052 transformers.

MAGNETIC FIELD FREQUENCY (Hz)

1k

10k

100k

100M

1M

10M

DISTANCE = 1m

DISTANCE = 100mm

DISTANCE = 5mm

1000

100

0.1

1

10

0.01

Figure 32. Maximum Allowable Current for

Various Current-to-ADM3052 Spacings

With combinations of strong magnetic field and high frequency,

any loops formed by PCB traces can induce error voltages large

enough to trigger the thresholds of succeeding circuitry. Care

should be taken in the layout of such traces to avoid this possibility.